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ELECTROPHILIC DISPLACEMENT REACTIONS: PART I KINETICS AND MECHANISM OF THE BASE AND METAL ION CATALYZED PROTODEBORONATION OF ARENEBORONIC ACIDSPART II: KINETICS AND MECHANISM OF THE PROTONOLYSIS OF TRIALKYLALLYLTINS
JOHN ANDRE MANGRAVITE
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Recommended Citation MANGRAVITE, JOHN ANDRE, "ELECTROPHILIC DISPLACEMENT REACTIONS: PART I KINETICS AND MECHANISM OF THE BASE AND METAL ION CATALYZED PROTODEBORONATION OF ARENEBORONIC ACIDSPART II: KINETICS AND MECHANISM OF THE PROTONOLYSIS OF TRIALKYLALLYLTINS" (1965). Doctoral Dissertations. 815. https://scholars.unh.edu/dissertation/815
This Dissertation is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. This dissertation has been ... , „ . j 66—5973 microiumed exactly as received MANGRAVITE, John Andre, 1939- ELECTROPHILIC DISPLACEMENT REACTIONS: PART I; KINETICS AND MECHANISM OF THE BASE AND METAL ION CATALYZED PRO- TODEBORONATION OF ARENEBORONIC ACIDS. PART II; KINETICS AND MECHANISM OF THE PROTONOLYSIS OF TRIALKYLALLYLTINS. University of Now Hampshire, Ph.D., 1965 Chemistry, organic University Microfilms, Inc., Ann Arbor, Michigan
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PART I: KINETICS AND MECHANISM OF THE BASE AND METAL ION CATALYZED PROTODEBORONATION OF ARENE- BORONIC ACIDS PART II: KINETICS AND MECHANISM OF THE PROTONOLYSIS OF TRIALKYLALLYLTINS
BY / JOHN ANDRE MANGRAVITE
B. S., Saint Peters College, 1961
A THESIS
Submitted to the University of New Hampshire In Partial Fulfillment of The Requirements for the Degree of Doctor of Philosophy
Graduate School Department of Chemistry June, 1965
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■ .i . L - L 1.1.. / /
Director of Thesis Research / -'______
Date
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I should like to express my sincere thanks to Dr. Henry G. Kuivila whose help and guidance during the course of this research has proven invaluable to myself, both professionally and personally.
I should also like to thank the Air Force Office of Scientific Research for their support of this research under contract AF 49 (638)-312, and the Atomic Energy Com mission for their support under contract AT(30-1)-2970.
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Page PART I
LIST OF TABLES...... viii LIST OF FIGURES...... x INTRODUGTION...... 1 RESULTS AND DISCUSSION...... 4 I. BASE-CATALYZED PROTODEBORONATION OF ARENEBORONIC ACIDS...... /, 1. Course of the reaction...... 4 2. Reaction system...... 6 3. Kinetic order of the reaction...... 6 4. Effect of pH...... 8 5. Effect of buffer concentration...... 11 6. Effect of substituents...... 16 7 . Mechanism...... 19 8. Conclusion...... 28 II. METAL ION-CATALYZED PROTODEBORONATION OF ARENE BORONIC ACIDS...... 35 1. Course of the reaction...... 35 2. Reaction system...... 35 3. Kinetic order of the reaction...... 36 4. Effect of cadmium ion...... 36 5. Effect of pH...... 36 6. Effect of substituents...... 39 7. Effect of other metal ions...... 43 8. Mechanism...... 48 9. Conclusion...... 57 EXPERIMENTAL...... 61 I. MATERIALS...... 61 1. Water...... 61 2. Areneboronic acids...... 61 3. Malonic acid...... 61 4. Sodium hydroxide...... 61 5. Perchloric acid...... 61 6. Sodium perchlorate...... 61 7. Metal salts...... 61
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II. GLASSWARE CLEANING PROCEDURE...... 62 III. pH MEASUREMENT...... 62 IV. BUFFERS...... 62 V. KINETIC PROCEDURE...... 62 1. Temperature control...... 62 2. Base-catalyzed hydrolysis...... 62 3. Acid-catalyzed hydrolysis...... 63 4. Metal ion-catalyzed hydrolysis...... 63 VI. CALCULATION OF RATE CONSTANT...... 63 BIBLIOGRAPHY...... 64 TABLES OF DATA...... 142
PART II
LIST OF TABLES...... 66 LIST OF FIGURES...... 67 INTRODUCTION...... 68 RESULTS AND DISCUSSION...... 73 I. CLEAVAGE OF ALLYLTINS WITH HYDROGEN CHLORIDE 73 1. Synthesis of allyltins...... 76 2. Reaction system...... 79 3. Course of the reaction...... 79 4. Kinetic procedure...... 83 5. Kinetic treatment...... 84 A. Aliquot method...... 84 B. Direct method...... 87 6. Substituent effects on the rate of cleavage of allyltins...... 87 A. Structure of the leaving group...... 95 B. Substitution on the allyl group..... 97 C. Cyclic allyltins...... 101 7. Effect of added metal ions...... 103 II. CLEAVAGE OF ALLYLTINS WITH DEUTERIUM CHLORIDE 110 1. Starting materials...... 110 2. Course of the reaction...... 110 3. Kinetic deuterium isotope effect...... 117 III. MECHANISM...... 125 vi
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EXPERIMENTAL...... 130 I. MATERIALS...... 130 1. Organotin substrates...... 130 2. Hydrochloric acid...... 134 3. Salts...... 134 4. Solvents...... 134 5. Trimethyl tin chloride...... 134 6. Deuterium oxide...’...... 134 7. Methanol-d...... 134 8. Deuterium chloride...... 136 II. GLASSWARE CLEANING PROCEDURE...... 136 III. PRODUCTS OF CLEAVAGE...... 136 IV. KINETIC PROCEDURES...... 137 1. Aliquot method...... 137 2. Direct method...... 138 BIBLIOGRAPHY...... 139 TABLES OF DATA...... 142
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Number Page
I. Pertinent ultraviolet spectral-data for areneboronic acids; wavelengths used in analytical determinations......
II. Effect of boronic acid concentration on the rate of protodeboronation of 2,6-di- methoxybenzeneboronic acid at 90.0°C....
III. Effect of pH on the protodeboronation of 2,6-dimethoxybenzeneboronic acid in aqueous malonic acid-sodium malonate buffers at 90.0°C., and ionic strength 0.14......
IV. Effect of variation of malonate buffer con centration on the rate of protodeboronation of 2,6-dimethoxybenzeneboronic acid at 90.0°C., pH 6.70 and ionic strength 0.14,... 12
V. Variation of the rate of protodeboronation of 2,6-dimethoxybenzeneboronic acid with malonic acid concentration at 90.0°C., pH 3.60 and ionic strength 0.14; buffer ratio (H„A)/(HA) 0.155...... :...... 13
VI. Values of kgxp. for the base-catalyzed proto deboronation of substituted benzeneboronic acids in aqueous malonic acid-sodium malonate buffers at 90.0°C., pH 6.70 and pH 6.42, and ionic strength 0.14...... 17
VII. Relative specific rate constants in protode boronation of 2,6-dimethoxybenzeneboronic acids in aqueous malonic acid-sodium malonate buffers at 90.0°C., pH 6.70 and ionic strength 0.14...... 23
VIII. Relative specific rate constants in protode boronation of 2,6-dimethoxybenzeneboronic acid at 90.0°C...... 34
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IX. Effect of cadmium ion on the rate of proto deboronation of 2,6-dimethoxybenzeneboronic acid at 90,0°C., in I.00 x 10"^M perchloric acid...... 38
X. Effect of pH on the protodeboronation of 2, 6-dimethoxybenzeneboronic acid at 90.0°C. in perchloric acid, in the presence of 1.00 x 10“4m cadmium ion...... 42
XI. Values of for the base -catalyzed proto deboronation of substituted benzeneboronic acids in aqueous malonic acid-sodium malonate buffers at 90.0°C., pH 6.70 and ionic strength 0.14; in the presence of cadmium ion...... 44
XII. Effect of metal ions on the rate of protode boronation of 2,6-dimethoxybenzeneboronic acid at 90.0°C., pH 6.70 and ionic strength 0.14...
XIII. Values of k^^ for the base-catalyzed proto deboronation of substituted benzeneboronic acids in aqueous malonic acid-sodium malonate buffers at 90.0°C., pH 6.70 and ionic strength 0.14; in the presence of cadmium ion...... 50
XIV. Relative specific rate constants in protode boronation of 2,6-dimethoxybenzeneboronic acid at 90.0°C.; k^''^ included...... 59
IX
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lo Pseudo first order rate plot for the base- catalyzed protodeboronation of 2,6-dime.thoxy- benzeneboronic acid (Run 90)..
2. log Rexp. versus pH for the protodeboronation of 2,6-dimethoxybenzeneboronic acid in the pH range 6.70 to 2.00...... 10
3. Test of Bronsted catalysis law for 2,6-di- methoxybenzeneboronic acid at 90.0°C., with malonic acid-sodium malonate buffers; pH 3.60 and ionic strength 0.14...... 15
4. log (Rexp.-Z^OexpP versus Cf for the base- catalyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C.... 18
5. log versus O' for meta and para substituted benzeneboronic acids in aqueous ethanol...... 24
6. log (R^/Rq’) versus O' for the base-catalyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C...... 25
7. log (Ri/Ro^) versus O' for the base-catalyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C..... 26
8a. log (R^/Rq’) versus O ' + 0.2 ( cr - O') for the base-catalyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C. 29
8b. log (R^/R *) versus O'+ 0.5( O'^ - O' ) for the hase-cataîyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C. 30
8c. log (Ri/R ?) versus O' + 0.8(0' - O') for the base-catalyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C. 31
9. Psuedo first order rate plot for the cadmium ion catalyzed protodeboronation of 2,6-dimethoxy benzeneboronic acid (Run 144)...... 37
X
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10. log kgxp versus pH for the cadmium ion cata lyzed protodeboronation of 2,6-dimethoxy benzeneboronic acid in the pH range 6.70 to 2.01...... 40
11. pH-rate profile for the cadmium ion catalyzed protodeboronation of 2,6-dimethoxybenzeneboro nic acid at 90 .0°C. (schematic)...... 41
12. log (Rgxp ^^Ogx ^ versus Cf for the cadmium ion catalyzed^protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C...... 46
13. log (kcd/^OQ^) versus Cf for the cadmium ion catalyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0“C.... 54
14. log (kcd/koQ^) versus O''^ for the cadmium ion catalyzed protodeboronation of meta and para substituted benzeneboronic acids at 90.0°C.... 55
XI
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The aromatic boronic acids undergo a number of reac tions in which the boronic acid (dihydroxyboron) function is replaced.^ Some of these, such as the brominolysis^'^;4,5 and iodinolysis^, have been shown to have the characteristics of typical electrophilic aromatic displacements. Very probably these cleavages involve attack by molecular halogen in the rate-determining step on a quadrivalent boronate intermedi ate.^’ The arylmercuration of areneboronic acids apparently involves attack of an arylmercuric cation on a quadrivalent boronate anion in the rate-determining step.^ Protodeboro nation in highly acidic media involves a rate-determining proton transfer to an intermediate which possesses either a trivalent or quadricovalent boron, depending on the reaction conditions _ ^ , 9 ,10 reaction of areneboronic acids with hydrogen peroxide, on the other hand, clearly proceeds by a mechanism which does not possess the detailed characteristics of electrophilic aromatic substitutions.^^ 12 Ainley and Challenger have shown that the hydrolysis or protodeboronation of benzeneboronic acid proceeds in water at 150°, and is catalyzed by concentrated sodium hydroxide, concentrated hydrochloric acid, and by zinc and cadmium bro mides. Ammoniacal silver nitrate has been shown to be an effective catalyst for the protodeboronation of benzeneboronic acid as well as others of the arene series.^ ,14,15 Kuivila and Nahabedian have made a detailed study of the kinetics of the acid-catalyzed protodeboronation of areneboronic acids. They demonstrated that the hydrolysis of p-methoxybenzeneboronic acid and 2,6-dimethyoxybenzene-
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. boronic acid was subject to general acid catalysis. They also determined dependence on the Hammett Acidity function, Hq , substituent effects, solvent deuterium isotope effects and activation parameters. From these data they concluded that the reaction is an electrophilic displacement in which the rate-determining step is proton transfer from an acid to the boronic acid. In view of the interesting features exhibited by the protodeboronation of areneboronic acids in the acid region, it was decided to extend the study to more alkaline conditions. Reuwer^^ has studied the base-catalyzed protodeboronation of ten areneboronic acids in malonic acid-sodium malonate buffers at pH 6.70. He has also determined the dependence of the protodeboronation on ionic strength and pH in the range 6.80 to 4.42, for 2,6-dimethoxybenzeneboronic acid. During his investigation it was observed that the base-catalyzed hydroly sis of areneboronic acids is further catalyzed by certain metal ions. Consequently, he studied the kinetics of the base- catalyzed protodeboronation of the same ten areneboronic acids in the presence of cadmium ion. He also determined pH depen dence in the range 6.60 to 4.42 for the cadmium ion catalyzed hydrolysis of 2,6-dimethoxybenzeneboronic acid and dependence of cadmium ion concentration for the hydrolysis of o-methoxy- benzeneboronic acid. These studies have been extended to include the follow ing: (a) a study of the effect of meta-substituents on the rate of both the base and metal ion-catalyzed protodeboro nation, (b) an extension of the pH-rate profile from pH 4.42 to 2.00 for both the base and cadmium ion-catalyzed proto deboronation of 2,6-dimethoxybenzeneboronic acid, (c) an examination of the effect of malonic acid-sodium malonate
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. buffer concentration on the rate of protodeboronation of 2, 6-dimethoxybenzeneboronic acid at pH 3.60 and 6.70, (d) the effect of cadmium ion concentration on the rate of protode boronation of 2,6-dimethoxybenzeneboronic acid, and (e) a survey of the effects of other metal ions on the rate of proto deboronation of 2,6-dimethoxybenzeneboronic acid.
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I. BASE-CATALYZED PROTODEBORONATION OF ARENEBORONIC ACIDS
The kinetics of the base-catalyzed protodeboronation of benzeneboronic acids with the substituents, m-OCH^, m-F, m-CI, m-CHg, and 2,6-diOCHg, in aqueous malonic acid-sodium malonate buffers at 90.0°C., and in perchloric acid at 90.0°C. for 2,6-dimethoxybenzeneboronic acid have been studied. The ultraviolet absorption spectra of reactants and products dif fered sufficiently so that the reactions could be studied by measuring the change in ultraviolet absorption at selected wavelengths. Pertinent spectral data are to be seen in Table 1.
1. Course of the reaction. If the pH of the reac tion solution is maintained at less than 6.80, basic hydroly sis converts areneboronic acids to the corresponding arene, as shown in eq. 1. B(0H)2 H
+ HgO --- — --- -> o (1)
In more basic solutions in the presence of oxygen, Reuwer^^ has shown that a sizeable amount of phenolic product is also formed, as shown in eq. 2.
B (OH) ^ OH
^ + b (o h >2
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. w g CO X) •H U C W 00 CO CO 0 0 CD CO 1—1 rM CO uo u M o CTv 1—1 00 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The highest pH used in any of the runs described in this work was 6.70, At this pH, any phenolic product formed is in such low concentration that it is difficult to detect. With all the areneboronic acids used in this work, no phenolic product could be directly detected by ultraviolet spectral measure ments . 2. Reaction system. Areneboronic acids are suffici ently soluble in water to allow it to be used as solvent. This is fortunate since water is usually the solvent of choice in acid-base catalyzed reactions. Reuwer 16 has found, however, that ordinary distilled water contains materials that strongly catalyze the reaction. Consequently, all the water used in this study was redistilled from glass. The acidity of the medium was adjusted either by per chloric acid or malonic acid-sodium malonate buffers. At 90.0“C. the malonate buffers showed a detectable change in pH after six days due, presumably to decarboxylation of the malonic acid. Thus, initial rates were used in calculation of rate constants for the slower runs. Agreement of the ultra violet spectrum of the product with that expected was taken as confirmation that the reaction took the expected course. 3. Kinetic order of the reaction. The basic hydroly sis of areneboronic acids has been shown by Reuwer to be first-order in areneboronic acid. In buffered solutions the hydrolysis shows good pseudo first-order kinetics. Figure 1 shows a typical first order rate plot for 2,6-dimethoxyben- zeneboronic acid. As shown in Table 11 (runs 130 Rand 131 R), the first-order rate law is valid over at least a 10-fold variation in initial concentration of 2,6-dimethoxybenzene boronic acid. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.3 I Fig, 1. Psuedo first order ro.te rlet for tPe eoso-cr.toDu'sod pr ot od : b or or ot ion of 2^6-d:'Jo.cthc:r/ecusereborenie o.oid o.t v0„0 decrees. ( Pur. 00 ). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE II Effect of Boronic Acid Concentration on the Rate of Protode boronation of 2,6-Dimethoxybenzeneboronic Acid at 90.0°C. Concentration of 2,6- Dimethoxybenzeneboronic 10 k , Acid = Run______moles/liter (sec" ) -3 130 R^ 4.45 X lO"^ 18.2 4 131 R^ 5.25 X 10"^ 18.3 90 4.45 X 10"^ 19.2 a from ref. 16. 4. Effect of pH. The effect of pH on the hydrolysis of 2,6-dimethoxybenzeneboronic acid in aqueous malonic acid- sodium malonate buffers at 90.0°C., and ionic strength 0.14, has been determined by Reuwer^^ in the pH range 6.70 to 4.42. In this work the pH-rate profile has been extended from pH 4.42 to 2.00. The data are summarized in Table III and illus trated in Figure 2. From pH 6.70 to about pH_5.90, the reac tion is first-order in hydroxide ion concentration. Below pH 5.90, the rate does not decrease as rapidly as it would if directly proportional to the hydroxide ion concentration. A minimum is reached at pH 4.85 and the slope then rises again to a negative unit slope below pH 3.50, Apparently in the pH range 3.50 to 4.85 a pH-independent reaction becomes important, since in this region the rate constants are somewhat larger than the expected contributions from the base- and acid-catalyzed Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reactions. The value for the uncatalyzed rate constant is — 6 “1 0.630 X 10 sec. . This value has been used in construct: the solid line in this pH region, seen in Figure 2. TABLE 111 Effect of pH on the Hydrolysis of 2,6-Dimethoxybenzeneboronic Acid in Aqueous Malonic Acid-Sodium Malonate Buffers at 90.0°C., Ionic Strength 0 .14 10^ k , (sec. Run pH obs. ^ kobs. 118R, 119R^ 6.70 18.1 1.258 13 3 R^ 6.42 9.36 0.971 137R* 6.05 4.25 0.628 136R* 5.85 3.05 0.484 140R* 5.45 2.04 0.310 14IR^ 4.42 1.78 0.250 82 3.81 3.66 0.563 78 3.55 5.96 0.775 20,22 3.00^ 20.7 1.316 26 2.70^ 34.5 1.538 24,21 2.40^ 90.2 1.955 23 2.00^ 230 2.362 ^ from ref. 16. b , these runs were carried out in the absence of buffer; perchloric acid was used to adjust the acidity. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10 1.6 leg 6 0.8 \ 0 2.0 »0 hcO >.0 6.0 ?c i'lg. 2. Leg k ae t)k for the -.I'o': ;L?Loro:ir.b:.en of 2.6-fl ooc benzeneboronic r.cfd in iho -f; re.n.ge 6.70 io 2.,CO. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 5. Effect of buffer concentration. As a test of general base catalysis versus specific lyate ion catalysis the effect of variation of buffer concentration on the rate coefficient for the hydrolysis of 2,6-dimethoxybenzeneboronic acid at pH 6.70 was examined. The results are seen in Table IV. When malonate anion concentration was varied ten-fold, no noticeable effect on the rate is observed. This is seen in the last column of Table IV. The rate coefficient, cor rected to pH 6.70 and ionic strength 0.14, is substantially -3 -3 the same between 0.155 x 10 M. and 1.55 x 10 M. malonate anion concentration. 17 As a test of the Brbnsted catalysis law for the hydrolysis of 2,6-dimethoxybenzeneboronic acid, the buffer concentration was varied at low pH. The data presented in Table V were obtained with a buffer containing the malonate monoanion and malonic acid in a ratio of 6.45, resulting in a pH of 3.60. A very pronounced increase in rate results as the buffer concentration is increased almost 300 fold. This is a clear-cut indication of general acid catalysis, and con firms the results of Kuivila and Nahabedian.’^ A plot of the data is shown in Figure 3. A linear relationship between rate and buffer concentration would be expected. The reason for the non-linearity of the plot at low buffer concentration is not clear. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 CO u •H cQ d CO O T—i o 30 C33 Ü I—I I CO Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 X . 4J /—N d X X d X 3 ' X o cn r-v m <1- T—4 01 U 1— I 1-H CO VO 1— 1 CO 1—1 <1- r—1 r-» m cn m VO O X X 1 g •d in in VO Oh 00 Oh CM 00 cn o m CN r4 CM •pH o X O 1—1 rH rH t—1 T—4 1—1 CM w c o Q) c m o o o •H d do 0 X 4-1 w 00 X d O r—4 1 1-4 CNOCM m g 01 1 1 1-4 1-4 vO (Jh VO m CM o CM 1-4 Oh 00 Oh N d LO 1 d 4-1 ui X o 1 m VO 00 CO a\ CN n- <1- Oh 00 CM 1—4 1-4 01 c/l QJ 1—4 1-4 1-4 1-4 1-4 CN o o X • d d X o il 0) . B /---s \ Ü •r4 1 cd X P O -x cd m 00 co X vO X <|- ro Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14 d Od o cn CM VO T—1 o o <1- •d- m LO X cn LO LO o- CO rO Oh LO Oh vO ) u Oh LO VOVO O QJ CM LO LO O- tH CO X 01 X) 4J QJ d 0 • o C \ O •ri •H cd 1—1 X 44 ^ cd cn iH 1—1 VO 1—4 d d CJ 1—4 o 1—4 LO cn •ri X o 1 ••••• X o LO lO LO LO 30 VOÜ 1 O 0) g r—i CO X U d 44 > C/J d w o O P •ri •H PQ X C < CO 0 O H cd LO CM o LO œ d •rH QJ VOVO LO LOLO 01 6 ••••• d X) X cn cn cn cn cn c X cd 01 N o X VO m VO O vo r—I CNJ CM en Cd en X U 44 o o o o • *H QJ Cd X 44 O a r d r d r d C < •r4 44 44 44 44 O 1—4 o < r o VO 4 - o t o t o t o 04) U O ■ O u d d d d •ri CO 0 0 O' o VO 'd ' c n 0) QJ QJ Q) X d QJ 1—4 -d- LOLO X X J 54 54 54 U O O 1—4 QJ 44 44 44 44 1—I X O L4-I 44 CQ CQ CQ CQ d B O Ü % QJ CJ O O u QJ 54 •H•H•H •H 44 54 d d d d cd OO o O o X—\ 54 Ü •H•H •i4 •r4 CJ X ) QJ M-4 d ' w ' /—N x - x X—N d VO CO O' < t O h cd rO ÜXJ QJ (44 Vw/ pp| 0 0 CO COCO CO Vw/ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 ob: ,1 C 20 !,n /•-o 10 Zbl.ozlc c.cld cc:~ ,,, r.olos/2.: FIs* 3* Tost of Erp'r-sted Ccbclyris I:;.r bcnsazsborcLCC o.cid -:1th r'::.lr:,l.c acll-c ::3 .6o and icnlc strength 0»l’.u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 6 . Effect of substituents. The rates of hydrolysis of four meta substituted benzeneboronic acids at pH 6.70 and 90.0°C. in aqueous malonic acid-sodium malonate buffers are summarized in Table VI. Included in this table are the rates of hydrolysis of four para and four ortho substituted arene- boronic acids under the same conditions as determined by Reuwer.^^ In order to ascertain whether the reaction followed was only the one whose rate coefficient increases linearly with hydrogen ion concentration, Reuwer^^ has measured the rates for the para and ortho substituted areneboronic acids at pH 6.42. The values found at this pH are shown in the third column of Table VI. In the fourth column are shown the values which would be expected at this pH assuming linear de pendence of rate coefficient on hydroxide ion concentration. The agreement between the expected and observed values is satisfactory, and assures that the rate of the same reaction is being measured in each case. The rates of the hydrolysis of the meta substituted areneboronic acids were not measured at the lower pH, because the reactions were too slow. However, it is probably safe to assume that the result would be the same. Examination of the values in the second column of Table VI reveals that all substituents increase the rate. In Figure 4, log (k /k )for the meta-and para-substituted ^ ^ exp. o exp.------^--- benzeneboronic acids is plotted versus Hammett's substituent constant. O' . This plot illustrates the point that both electron-withdrawing and electron-releasing substituents in- c crease the rate of reaction. Obviously no simple linear free energy relationship will correlate these data with those for other electrophilic aromatic substitutions. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 c n T> CM •H CM g < . OO OO VO T— 1 OO CO CN vO o VO CN LOOO 1—4 ON CO o VO •H O VO CN < N r 4 O OO OO OOOO OO r-4 C ÇU O P. X o OOOO j—4 o 1— 1 1— 4 o o o O k O O g bO O g O N 1^ C (1) M3 CQ X T3 cx (U U P • 1 XJ CJ u v O o I— 1 CO CO •H 0 o CN OO OO CT n o CO CN XJ o 0 ) o CO r - 4 r — 4 O 0 0 1— 1 LO CO v O C O X i o O CN o o o o o o o ' d ' p o> CQ CH 4 eg - ) M3 X c n cu c n CM. •H cu CN in r — 4 O CN CO c n M-l g ' CO CN < t o o VO >, mm u o OO 1— 1 1— 4 1— 4 CN r - - P Q) 0 CQ M 3 CO o o o OO o O 3 k CQ m) CU Cm 4-1 PS e g C T) 0 cu I— I . N e g Cm S p H 1— 1 O 1—I X 1 LO o O O o OO v d CN e g 0 ) 1— 4 v O L O CO OO v O O < 1 * OO r — 4 4 - 1 o v O 1— 4 v O CN C N 1— 1 m OO 1— I v O OO CN OO CN e g 1 CD CP " 0 '43) CO X OOOO o 1— 1 o 1— 4 CO o OOO 1 0 o P 1— 4 CU CQ r - 4 c n 1 e g T) CQ •r4 U cu X < 4 - 1 cud k d P CO O o 4 M PS PS OO X CO M-4 r-M •H o PS CP X 1— 1 o X 1— 4 4 M 0 U Pm U 0 a p q u o u U • S c n 1 I I I 1 M 3 CM CM CM CM CM o o o o è é k B X c n 'P (U p CQ O Mm CU MM p X O cr < o6 c u p c d P P P P P P P U V w / » P •H p ' w ' ' w ' s - / d O O 1— 1 C N M - l p XXX X XXXX X C O O O o O O O C d X v O CNVO o \ m CO OO > m < 1 - ' d d m d < t d d C O VOP r - 4 1 - 4 1— 1 1— 1 1— 4 1— 1 1-4 r-4 1—4 r-4 1 - 4 1— 4 1— 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 r-CILO 0.6 0.5 OoU leg 0.2 0.1 o - 0. 1'. - 0.2 0.2 Ocô Flgo h> Log (k /k° ) rcrc-j 000. oboo to:: t'lo co.co-c' d.Gboror_ation o:C r v r.:/ TC:::LO a t 90.0 dcgrecc. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 7. Mechanism. The linear relationship between pH and log in the pH range 6.70 to 5.90 suggests the following two-step mechanism as a reasonable working hy pothesis . Ka ArB(OH)„ + 2H_0 ^ = ± ArB(OH)„ + H„0 (3) ^ ^ fast ^ ^ ArB(OH)“ + HgO ArH + B(OH)g + OH" (4) In the following analysis, the symbols to be used include: (BAH) concentration of free areneboronic acid, ArBCOH)^ (BA ) = concentration of areneboronate anion, ArB(OH)" (BAH) = stoichiometric concentration of areneboronic ® acid, [ArB(0 H)2 + ArB (OH)"] k , = observed rate constant obs. In the above mechanism, a water molecule attacks the arene boronate anion in the rate-determining step. Consequently we can write Rate = V = k'(BA“)(H^O) (5) For reaction (3), Since \ = (H^)(OH") (7) and consequently (Hh ^ ^ (8 ) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 we get by substitution in eq. (6 ) K (BA") w (BAH) (OH") - or K (BA") = ^ (BAH) (OH") (10) w Since (BAH) = (BAH) - (BA") (11) we get by substitution in eq. (1 0 ) K (BA") [(BAH)g - (BA")] (OH") (12) w Rearranging, K K (BA") = (BAH)^(OH") - ^ (BA )(0H") (13) w w R K (BA") [1 + ^ (OH")] =^ (BAH) g (OH") (14) w w K ^ (BAH)^(OH") (BA") = ------(15) K 1 + ^ (OH") w Now since the highest pH used in this work is 6.70 and the pK values for the boronic acids are greater than 8.25, the ^ Ka term — (OH ) in the denominator can be neglected. Consequently w we can write K (BA ) = —— (BAH) (OH ) (16) Kw s Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21 Substituting eq. (16) in eq. (5) gives K Rate = V = k' ^ (H^O)(BAH)^(OH ) (17) Since the concentration of water remains constant at 55.5 moles/1., K Rate = V = 55.5 k' ^ (BAH)^(OH") (18) w The basic hydrolysis of areneboronic acids was found experi mentally by Reuwer^^ to be first order in areneboronic acid, and so the experimental rate expression can be written. Rate = V = k^^g(BAH)g (19) Comparing eq. (18) with (19) we find hbs. “ ''' r (OH') (2 0 ) w Substituting eq. (5) gives 55.5 K^k' ^obs. " (ff»T“ ^ (2 1 ) k ^ (H+) k' = -2^ - (2 2 ) 55.5 K a 19 Polevy has measured the ionization constants of areneboronic acids. Since he determined the constants in 25% methanol at 25°C., and the kinetic runs in the present work were made in aqueous solution at 90.0°C., the absolute values of k ’ cannot be accurately obtained. However, the relative values should be significant, and sufficient for the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 purposes of the present work. The values of k', calculated from and k^^^ using eq. (22), are listed in Table VII. Included in this table are the values of k' obtained by Reuwer^^ for the ortho and para-substituted areneboronic acids. The values of for meta-methyl- and meta-chloro- benzeneboronic acid were not determined by Polevy, but these values may be interpolated from a plot of the pK^ values of the other substituted areneboronic acids versus Hammett's substituent constant, CT . Such a plot is illustrated in Figure 5. Inspection of the values of log (k'/k'^) in Table VII shows that the normal pattern for electrophilic aromatic substitution emerges. In Figure 6 , log (k'/k'^) for meta- and para-substituted areneboronic acids is plotted versus O' . A good straight line is obtained with the point for benzene boronic acid falling below the line. 20 Brown and Okamoto have developed a series of sub- ~r* stituent constants o' , which are corrected for resonance stabilization of an electron deficient transition state. In Figure 7, log (k'/k'^) is plotted against In this plot the point for p-methoxy lies considerably below the line. It thus appears that cr does not correlate the data as well as O' . Wepster^^ has suggested that O' and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 TABLE VII t Values of k for the Basic Hydrolysis of Substituted Benzene boronic Acids in Aqueous Malonic Acid-Sodium Malonate Buffers at 90.0°C., pH 6.70 6 ^ AO (a) 10 k Substituent ^a 1.mole~^sec. log(k /k p) H^b) 7.59 0.688 0.0 2.57 8.54 1.09p-OCHg(b) p-CH^t^) 3.02 3.10 0.654 p-p(^) 9.33 0.966 0.149 p-Cl(^) 20.9 0.322 -0.330 o-OCH.(b) 2.14 25.8 1.58 o-CH-(^) 1.02 12.6 1.27 o-p(^) 56.2 7.14 1.02 o-Cl(b) 26.9 12.0 1.24 m-OCHg 16.6 0.744 0.034 m-CH^ 7 .0 8 (c) 1.50 0.338 m-F 57.5 0.208 -0.520 m-Cl 5 1 .3 (c) 0.152 -0.656 (^^ from Ref. 19 (^^ from Ref. 16 (c) interpolated from plot of pK versus sigma; Kq=7.59 x 10 yC* - -2.95; (see Fig. 5) ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 10.0 9.0 o cjzicriLTontal "'a..uc C') izitcmclatc 8.0 .0.4 - 0,2 n o A LO" 9» Loc Tcro-aa c±r\-?. fc: C-Ciclô ia arrj.^O’.'.a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 1.2 0.8 log k'A' 0 0,3 Fig. 6 . Log k'/k' vorouo r ?o :e:.c.:cr('T. '.icn of r.ota and rara nabciiiatcd cornt.ioboronic aoido ai ÇC,C do;;;; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 1.2 0 \ o 0.8 Fig, 7. Log k '/k^ vcrcv.c : for i'-.o 'rrnc-cn'-.-'.ly-cd nroicdcbcrcr.v.v.i-■. of Kcto. and oarr. :.iiuiod borncncboronio ; oi '.: ai 70.0 dr'n’ec Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 line determined by the points representing meta substituents. This they attributed to the possible lesser importance of transition state resonance in this reaction than in the reac tion used to obtain (y , (namely, the solvolysis of 2 -phenyl- 20 2-propyl chlorides in 90% acetone at 25°). They cited other reactions in which the resonance effect appeared to be less than predicted by cy^ values. These examples included 25 the solvolysis of neophyl brosylates , the Beckmann re arrangement of acetophenone oxime picryl ethers and the 27 acid catalyzed rearrangement of phenylpropylcarbinols. 4 Conversely, in the brominolysis of benzeneboronic acids , the contribution of transition state resonance appears to be greater than predicted by O' . On the basis of this evidence Yukawa and Tsuno suggested that a single set of O' values was not sufficient to correlate all reactions in which reso nance stabilization of an electron-deficient transition state is possible. They developed a modified Hammett equation which might correlate electrophilic reactions in general: log (k/kg) = O' + r(cy^ - o' ) (23) where r is a reaction constant measuring the degree of transition state stabilization by resonance. Thirty-five reactions have been correlated by eq. (23), The reaction constant r was found to vary over a wide range (0.2 to 2.3) for the reactions studied. Yukawa and Tsuno be lieve that Brown and Okamoto's equation is successful only because most reactions have r values in the relatively narrow range of 0.7 to 1.3. In Figure 8 , log^kt/k'^) for the basic hydrolysis of meta and para-substituted areneboronic acids is plotted versus cy + r(CX^ -O'), where r is varied from 0.2 to 0.8. A -j- better correlation is obtained than with O' ; however, the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 best line is obtained when just (y is used. The value of in Figure 6 is -2.32. This negative value of indicates that a positive charge develops at the benzene ring in the transition state. The magnitude of the charge is a relatively small one for electrophilic aromatic substitutions which usually have values larger than four. Displacements of silicon, germanium, tin, and lead from the benzene ring by the proton have values of -5.0, -4.6, -3.8, 29 30 31 32 and -2.5, respectively. ’ ’ ’ Protodeboronation of benzeneboronic acid in 6.3 N sulfuric acid at 60.0° has a + 8,9,10 value of -5.0 and the rates are correlated best by o' The decrease inwhen the more reactive areneboronate anion is the substrate would be expected because the negative charge on the boronate anion decreases the electron demand at the seat of reaction. 8 , Conclusion. Kuivila and Nahabedian^ ? 9,10 established that the acid-catalyzed protodeboronation of areneboronic acids involves a rate-determining proton trans fer from acid to boronic acid. This conclusion is supported in the present work by the observation of a linear dependence of rate of reaction on hydrogen ion concentration in the pH range 2.00 to 3.50, and the fact that when malonate buffer is varied 300-fold at pH 3.60 a very pronounced increase in rate is observed. The base-catalyzed reaction, on the other hand, appears not to be subject to general base catalysis. Above pH 5.90, it seems almost certain that the reacting species is the boronate anion. This mechanism represented by equations (3) and (4) with reaction (4) rate-determining is supported by the following facts. Above pH 5.90 the rate of reaction is proportional to hydroxide ion concentration. A variation of buffer concentration at the same pH leads to no change in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29 1.2 0.8 k) o 0 0.3 ~ 0 . 6 -Ok' 0.,2 Fis* 8 , Les k ’/!-* Tcrcr.c C^-;-C,0 '-S'') :L oj? ne ta ar/.I cua^a-j. .•.’..vooci jcnr C'' f t . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 1.2 0.8 0 h Oc8 - 0,6 'J.. Fig, 8 o Log k'/!:' vcrcv.o rf ' - C'"'} For 'F:':' c',::c :o%r b o of Kcba r.nd ro"o crb':-M':vLcà cor rcr.oboro:;f.c ne:' Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 0.8 Oeii O 0 r o 0.6 r ■*> c..l( c-') ’:1s. 8 , Los k ' A ' vcrov.c Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 rate (except for small changes due to a change in ionic strength). An increase in base concentration thus results in an increase in rate only when it leads to an increase of areneboronate anion through an increase in pH. Reaction (4) might very well be subject to general acid catalysis, but this possibility has not yet been examined explicitly. In the areneboronate anion, the carbon adjacent to the boron should be more susceptible to electrophilic attack because its electron density has been increased by the in ductive effect of the negative charge on boron. If a water molecule is donating a proton to the areneboronate anion in the rate-determining step, the transition state will possess a negative charge. This agrees with the observed kinetics. Two possible extremes for the transition state are represented by I and II. In I the benzene ring contains a II positive charge directly on it and resembles an S*E2 trans- 33 sition state. In this case_y^ for the reaction would have a large negative value and the rates would be correlated by . In II, the benzene ring does not contain a positive 33 charge and resembles an SE2 transition state. In this case Ji for the reaction would be closer to zero. The experimental value of y is -2.32. This value is small compared to t h e ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 of -5.0 found for the acid-catalyzed hydrolysis.^^ T h e low value of in the base-catalyzed reaction is evidence that the transition state in this reaction resembles II more than does the transition state in the acid-catalyzed reaction. The satisfactory correlation of the rate constants with the "normal" sigma constant, O' , is added proof that the positive charge in the benzene ring is not highly developed. An SEl type of mechanism (eq. (24-26)) can be elimi nated as a possibility because it would be expected to have a positive value o f , whereas a negative value has actually been observed. B(OH) B(OH). + OH (24) slow ^ + B(OH) (25) + H O + OH (26) In the region of pH 5.90 to 3.60, a pH-independent reaction becomes important. This independence of pH could be explained by either of two mechanisms. In either case this uncatalyzed reaction must have a transition state which is neutral over all. This could result from attack by a water molecule on a boronic acid molecule, or from attack by hydronium ion on a boronate anion. Certainly a hydronium ion and a benzeneboronate ion are a more reactive pair than a water molecule and benzeneboronic acid molecule. The con centrations, however, of boronic acid and water are much greater than the concentrations of boronate anion and hydron ium ion. The question is whether the greater reactivity of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34 the boronate anion-hydronium ion pair predominates over the greater concentration of water and boronic acid. The magnitude of the difference of the reactivities of the various species present in aqueous solution can be seen in Table VIII. In this table rate constants for 2,6- dimethoxybenzeneboronic acid at 90.0°C. have been calculated for the four pairs of reacting species indicated. It should be realized that these rate constants hold only for the specific areneboronic acid used, namely, 2 ,6 -dimethoxyben zeneboronic acid. Perhaps the only conclusions which can be drawn from these data with any confidence are that the boronate anion is about a million times as reactive as the boronic acid molecule and the hydronium ion is about a million times as powerful an electrophile as water in aromatic protodeboro nation. TABLE VIII Relative Specific Rate Constants in Protodeboronation of 2,6- Dimethoxybenzeneboronic Acid at 90.0°C.^ Reactants k liters/mole sec. ArB (OH)2 H3O* 2. 12 X 1 0 “^ ArB(OH)3 H2O 2.24 X 1 0 "^ -8 ArB(OH)2 1.15 X 10 ^2° ArB(OH)3 H^O^ ' 7.0 ^ the absolute magnitudes of these rate constants have no significance inasmuch as pH measurements were obtained at 25°, and the values of used in the calculations were obtained at 25° in 25% ethanol, whereas the kinetic measurements were made at 90.0° in water, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 II. METAL ION-CATALYZED PROTODEBORONATION OF ARENEBORONIC ACIDS Reuwer^^ has shown that the presence of catalytic amounts of certain metal ions greatly increases the rate of the basic hydrolysis of areneboronic acids. In the present work an extension of his examination of the reaction cata lyzed by cadmium ion is presented. Also included is a sur vey of the effects of other metal ions on the rate of proto deboronation of 2,6 -dimethoxybenzeneboronic acid. The kinetics were followed using the spectrophotometrie technique described in the experimental section. Pertinent spectral data are seen in Table I. The rate constants for the cadmium ion reactions (k^'^ ) were calculated by taking the difference between the observed rate constant and the rate constant for the cor responding base hydrolysis, and dividing by the cadmium ion concentration. The reaction whose rate constant was calcu lated in this manner is hereafter called the "cadmium" reac tion . 1. Course of the reaction. In the pH region used in this study, hydrolysis due to cadmium ion catalysis con verts areneboronic acids to the corresponding benzene. The products, thus, are the same as in the normal base hydrolysis. 2. Reaction system. The reaction system used in this work was the same one as that used to study the base hydrolysis. The metal ions were added as nitrates in order to minimize complications, which might result from the presence of several different complex ions in the solutions. The nitrate ion has no effect on the rate since the presence of sodium nitrate did not affect the rate. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 3. Kinetic order of the reaction. The cadmium ion catalyzed protodeboronation of areneboronic acids has been 16 shown by Reuwer to be first order in both areneboronic acid and cadmium ion. In buffered solutions, the reaction is psuedo first order. Figure 9 shows a typical psuedo first order plot for 2 ,6 -dimethoxybenzeneboronic acid. 4. Effect of cadmium ion. Reuwer^^ has shown that with o-methoxybenzeneboronic acid at pH 6.70, addition of 1.0 -4 X 10 M cadmium ion increased the psuedo-first-order rate -6 -1 -6 -1 coefficient from 1.53 x 10 sec. to 42.4 x 10 sec. , and — Zf — 6 “ 1 addition of 5.0 x 10 M cadmium ion from 1.53 x 10 sec. to 203 X 10 “ 6 sec. “ 1 . This corresponds to a 4.87-fold increase in rate due to a five-fold increase in cadmium ion concentra tion. Data for the variation of cadmium ion concentration in the protodeboronation of 2 ,6 -dimethoxybenzeneboronic acid in perchloric acid solution is seen in Table IX. When cadmium ”4 ion concentration was varied a thousand-fold from 1.0 x 10 M to 1.0 X 10 ^ M, in the presence of 1.0 x 10 ^ M perchloric acid, an increase in rate is observed. Comparison of the values of shown in the last column suggests that this de pendence is probably linear at low concentrations but falls off at higher concentrations. The last three entries in Table IX indicates that at lower pH's there is no dependence of rate on cadmium ion concentration. In this region the acid-catalyzed hydrolysis predominates and the data indicates that this reac tion is not further catalyzed by cadmium ion. 5. Effect of pH. The effect of pH on the cadmium ion-catalyzed protodeboronation of 2 ,6 -dimethoxybenzeneboronic acid in aqueous malonic acid-sodium malonate buffers at 90.0°C., and ionic strength 0.14, has been determined by Reuwer^^ in the pH range 6.70 to 4.42. In this work the pH-rate profile has Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 O.h loz absorbance 0.8 TO T:.nc. j^i'lTav'-.cs Fig, 9. Pcuodo first order rate p?.o’:. for the cailrirji ion ca%alyccd proto- ',6-dinettc:-7b:r.';cneboronic acid at 90.0 do pro os. ( ivn l ’:!i ), Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 r—1 \ I T) ^ O o > 1 X—s X O e 0 iH d X •HX ■u ^ X g u 01 0 ) X} e u n d .... •rH X) < t o X—N a •r-1 I T t d OO < 01 X r> . < r <1- c n M3 CM rH C T3 0 01 CM 01 d . a XI -X 'r4 X r-l o O o c n o e n LO •H d 14-1 O 01 1 r d r—1 T—i rH rH tH o CM XJ 1 Cvj CM CM CD d 4 u o c X 4J d o 0 a 01 X X •r-i S-l CD Cl O 01 01 Ü d -X to p4 a 01 V—X o 01 o s u j q M V-i r o d • o I T) d w X o •H d o 01 Ü •H*H pq tS X CD o K E 4 - 1 o U d d o o 'd' CM CM jd" •H •H 14 Ph c d E P-I T3 X tH m CM vO 00 CM CM O KO o 01 X O O) I rH c n M3 (3^ tH u > d < 4 4 d c n CM CM 0 •H Cl X 0 •fH C 0 0 •H MD C 4-1 X Cl 01 1—4 d 4J 01 d 4 J cO 01 d X O •r4 •r4 X Cl (S 4-1 o X d •H O t 4 •r4 01 d 01 Ob d CM > o O f: •H 0 4 d 44 1—1 4 - 1 01 01 xt O 01 01 Cl d < r CJ d d o " 0 0 0 0 0 Ob c n VO IT) rH rH t—4 o X 01 •H rH rH rH rH rH fH o o Ob 01 d o a O 4J 4-1 44 s < c n c n c n c n c n c n CM CM rH d d d S M - d d 01 01 CM 4-1 •r4 •H 1 PO 1—I Cl O o ; d d *r4 •r4 rH *r4 01 4-1 144 >44 d d >44 >44 X 4-1 01 01 01 cO 01 B O O o U ■H Cl U o Ü d Mh •H 01 01 01 r 4 o CD d d , 44 44 (Ü Q) o X d d d O o o O •H 01 d d •H Ü 1—1 o O o O o O iH 01 ■s x-N X~S / m o rH m o o o o I—1 O a -O Cl X 01 m rH u n o rH -X V_x _ x M Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 been extended from pH 4.42 to 2.20. The data are presented in Table X. A semi logarithmic plot of the values of exp. versus pH is seen in Figure 10. The linear portions are drawn with the theoretical positive and negative slopes for speci fic hydroxide and hydronium ion catalysis, respectively. In the pH range 5.o0 to 3.10, a pH-independent reaction becomes important. The curved portion around the minimum in Figure 10 was drawn assuming this "uncatalyzed" reaction with a cal- — o “ X , culated specific rate coefficient of 6 x 10 sec. in addition to the catalyzed reaction. The lower curve in Figure 10 is the pH-rate profile for the normal base catalyzed reac tion. At any pH the difference in the vertical direction between the two curves represents the rate due to the pre- -4 sence of 1.0 x 10 M cadmium ion. A plot of these differences results in the pH-rate profile shown in Figure 11, in which the ordinate is the analytic specific rate constant for catalysis by cadmium ion. In this plot the values at high pH should be reasonably accurate, representing, as they do, data from reactions in which the cadmium ion catalysis domi nates the overall rates. In the region of the minimum and at lower pH values, the data are less accurate because the values represent small differences between larger numbers. 6 . Effect of substituents. The rates of hydrolysis of four meta-substituted benzeneboronic acids at pH 6.70 and 90.0°C. in aqueous malonic acid-sodium malonate buffers in the presence of cadmium ion were measured. The results are seen in Table XI. Included in this table are the results obtained by Reuwer^^ for the hydrolysis of four para and four ortho substituted benzeneboronic acids under the same con ditions. Inspection of this table reveals that both electron- releasing and electron-withdrawing substituents increase the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 2.2 C 6,0 D.ï .'ij,, J.O. Lo2 vci'sus p.î xoï* the ca&Tiiun ion catalyzed protodeboronation 01 2i6~iirùethoo"/-ûcnzenoboronic acid at 90.0 degrees. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 cd Cdv 0 3.0 h»0 5.0 6,0 pK Fig. 11» pll-rate profile for the cad'lum ion catalyzed protodeboronation of 2g6-cLL:Gthc:ybenzoneboronic acid at 90.0 degrees, ( schematic ), Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 TABLE X Effect of pH on the Protodeboronation of 2,6 -Dlmethoxybenzene- boronic Acid at 90.0°C., in the Presence of 1.00 x 10 Ca) Cadmium Ion , in Perchloric Acid 1 0 ^ exp. exp. -1 -1 -1 Run pH sec. sec. 1l.mole T - 1 sec 160 1.91 246 245 46 2. 2 0 176 151 250 47 2.47 82.4 67.4 - 150 48 2.91 42.1 35.1 70 45 3.10 19.5 18.2 13 51 3.18 15.4 10.4 50 52 3.62 13.4 5.10 83 164R^®^ 4.42 11.8 1.78 100 163R(^) 5.45 47.5 2.04 455 162p(^) 6.05 140 4.25 1360 161R^^) 6.70 6 9 8 18.1 6800 (a") ionic strength 0.14; initial boronic acid concentration 4.45 X lOr^M experimental rate coefficient Cc ^ rate coefficient observed rate coefficient due to added cadmium ion; )/ (Cd) “ P- from Ref. 16; in aqueous malonic acid-sodium malonate buffers Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 rate. This is the same type of behavior as was observed for the reaction in the absence of the metal ion. In Figure 12, log(k^^p /^oexp ) the meta and para substituents is plotted against Hammett’s substituent constant, CX . Obviously no simple linear free energy relationship will correlate this data. 7. Effect of other metal ions. The effects of a number of metal ions, other than cadmium ion, on the rate of hydrolysis of 2,6 -dimethoxybenzeneboronic acid at pH 6.70, and 90.0“C., were examined. Nitrates and perchlorates were used in order to minimize complications which might result from the presence of several different complex ions in the solutions. This precaution was not always essential inasmuch as copper(II) chloride and nitrate gave the same rate con stant within experimental error. Catalysis was observed when the following salts were used as addends : Ni(N0 g)2 , Mg(N0 2 )2 , Co(N0 2 )2 , Zn(N0 2 )2 , Pb(N0 2 )2 , Cu(N0 2 )2 , AgNO^ and CUCI2 . The results are sum marized in Table XII. In this table the experimental rate constant is shown in the third column. In the fourth column the catalytic rate constant is given. This is calculated from the following equation: k“ - 1 8 . 1 K lO'G ,, , hat. . -ÊSH--- (27) metal ion concentration As can be seen the order of effectiveness of the cations listed is copper(II) > lead(II) > silver ^ cadmium > zinc > cobalt(II)> magnesium > nickel(II). No specific rate constant is given for silver ion because of difficulties in measuring the rate due to formation of precipitate, but the very rough value obtained was of the same order of magnitude as that for cadmium ion. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 TABLE XI r ,Cd r Values 1of for' the Basic Hydrolysis of Substituted Benzene- boronic Acids in Aqueous Malonic Acid-Sodium Malonate Buffers at pH 6 .70, 90.0° C., Ionic Strength 0.14, in the Presence of Cadmium Ion 1 0 ^ (Cd^+) 10 ' i.g(kg"/kSg) Substi Run tuent moles/liter 1l.mole 1 sec. -1 165R(^) H 1.00 22.4 0 169R(^) p-CH_0 1.00 48.5 0.336 147 p-CHgO 10. 0 49.7 0.346 167R(^) p-CH^ 1.00 24.0 0.029 146 p-CH„ 10.0 25.0 0.045 J 166R(b) p-Cl 1.00 50.0 0.348 145 p -Cl 10.0 48.2 0.326 168R.(b) p-F 1.00 46.1 0.314 148 p-F 1 0 .0 49.7 0.346 81 m-CH^O 5.00 28.4 0.104 65 m-CHgO 1 0.0 31.9 0.155 66 m-CHg 5.00 19.6 -0.058 64 m-CHg 1 0.0 20.5 -0.041 79 m-Cl 5.00 39.4 0.246 63 m—Cl 1 0 . 0 35.0 0.193 80 m-F 5.00 12.3 -0.260 62 m-F 1 0 . 0 11.0 -0.302 continued Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 TABLE XI continued (a) 1 0 ^ (Cd^+) 1 0 ^ log(k^^/kSy) îubsti- -I -I Run luent moles/liter l.mole sec. 159R.(^) o-CH„0 1.00 410 1.26 170R.(^) o-CH„ 1. 0 0 54.5 0.387 171R^^) o-Cl 1 .00 752 1.52 181R(^) o-F 1. 0 0 1930 1.93 (a) rate coefficient due to added cadmium ion: (k^^ - k ) exp. exp. (b) from Ref. 16 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 P-- p-Cl 0.3 iz—Cl r> 0.1 •Oil, - 0.1 - 0.2 -0.3 -0 .4 - 0.2 0.4 Cd. cCd. Pig. 12. Log (Ic , /ic . ) vcirc-ao cigra fox* cadiTduiz Ion catalysed OOSi, 000» protodoboro:a.tic:T, of r.ota and p.aro. substituted benzeneboronic acids at 90.0 degrees» Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 TABLE X I I Effect of Metal Ions on the Rate of Protodeboronation of 2,6 -Dlmethoxybenzeneboronic Acid at 90.0°C., Ionic Strength 0.14, pH 6.70 (a) (b) Metal ion 1 0 ^ k exp. cat, concentration - 1 -1 Metal ion moles/liter sec. l.mole1 1 -1 sec Ni^+ 1.00 X 10'^ 23.0 0.0049 Mg^^ 1.00 X 10“^ 30.6 0.0130 Co2+ -1 .0 0 X 10“^ 51.3 0.0332 Zn2+ 1.00 X 10"^ 35.2 1.67 Cd2+ 1.0 0 X 1 0 "^ 70.3 5.22 Pb^+ 1.00 X lO"^ 236 21.8 Cu2+ 1.00 X 10“^ 416 39.8 (^)cu"+ 1. 0 0 X lO"^ 421 40.3 (a) average of values from four experiments, initial boronic acid concentration 4.45 x 10” M M .-6 . (b) k (k“ - 18.1 X 10 )/metal ion concentration cat. exp. (c) as chloride; average of values from two experiments Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 Kinetic data could not be obtained with the follow ing cations: Fe^^\ Mn^^, Pd^^, and Au^^. Upon mixing a _3 solution of 1,00 X 10 M palladium(II) chloride with 2,6- dimethoxybenzeneboronic acid a black precipitate appeared which turned silvery upon standing. Apparently the precipi tate is palladium metal formed by reduction of Pd(II) under the reaction conditions. With ferric nitrate no kinetic data could be obtained because its ultraviolet absorption masked that of the boronic acid. When manganous sulfate was used as addend the reac tion solution turned an increasingly deep brown color with time. _ 3 When chloroauric acid (1.00x10 M) was added to 2,6- -3 dimethoxybenzeneboronic acid (4.45 x 10 M) at room tempera ture a blue dispersion of metallic gold appeared immediately, and the odor of resorcinol dimethylether could be detected. When the concentration of the gold compound was decreased to — 0 1.00 X 10 M and the kinetics examined, the initial rate was found to be the same as the uncatalyzed rate, but increased with time after about 2 0 % reaction. No catalysis was observed when the following addends were used: NaNO^, KNO^, LiNO^, Al(NO^)^, Cr^NOg)^, H^PtClg. 8 . Mechanism. In view of the fact that mercuric salts react with areneboronic acids to form arylmercurials, 12 Ainley and Challenger suggested that other metallic salts react in an analogous manner forming easily hydrolyzed organo- metallic intermediates. Neglecting solvation, this mechanism can be written as follows: Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49 K a ArB (OH) « + 2H„0 ^---- ArB~(OH)„ + H o'*' (28) fast ^ 2+ Cd ArB (0H)„ + Cd --- > ArCd + B(OH) (29) ^ s low b ArCd^ + H O g _ ArH + Cd^+ + OH (30) By arguments analogous to those used for the base reaction we find that k“ (H+) = -5? . 5 K a An alternative to this mechanism is one in which the proto deboronation product is formed directly by proton transfer to the substrate from one of the ligand water molecules; i.e., the hydrated metal ion acts as a Bronsted acid. Considering only one of the hydrating water molecules this mechanism can be written as follows: K ArB (OH) „ + 2H„0 ArB~(OH)„ + H.O^ (32) ^ fast ^Cd ArB" (OH)- + C(^"^OH- --- > ArH + B(OH)„ + Cd + + OH" (33) ^ slow ^ Here again can be calculated from equation (31). Polevy 19 has measured the ionization constants of areneboronic acids in 25% methanol at 25°C. Using his values and the values of k^*^ obtained at 90.0°C. and pH 6.70, rela tive values of k^^ for the areneboronic acids used in this work can be calculated. These values are seen in Table XIII. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50 T3 CJ O ' d CU O CM cn Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 r—s X rH ÙO O cs| I 0 u 3 VO o ^ œ CM CTN O in CM X X O o CM CM o o Oh cn o cn I OO rH rH o o o o 00 Oh o X“N X-N rO QJ QJ Q) 0) X 3 X) CO CM g Cd VO VO OO cn CO LO lO rH O Oh CM •H • • •• • • •••••• X v O v D rH rH r - ' CM t- 4 '>D vO 3 o T—4 rH m LO lO CM LO o u o rH H cO X w X 13 w -d- Oh VO LO O CO o LO rH 1 0 0 rH Oh O Oh LO CM rH O CM O ; Q) CM CO r4 CM CO CO tH tH rH LOLO CO CO rH O' Oh J4 0) 44 o o o o o o o o 13 •H o o o o o o o o o o o o O rH X o X o X o X o 1—1 rH iH tH 'd* CO tH iH 1—1 \—I O Q) H H O B 44 Ü /-T\ Q) X X X 13 d 44 •H o o o 44 CO COCO CO cn X CO X X X W t—1 rH X fri rH o u o CJ o a fH Ph a CJ o P4 ap cn h B é B é 6 BB o o o O Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 + CM X U r4 X O CT\ 3 CM 3 X X -3 1 O 3 44 -X 3 11 1 t-4 X t-4 H—S 3 40 3 X 3 —k Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53 Also included in this table are the rate constants obtained by Reuwer , under the same conditions, for the para and ortho substituted benzeneboronic acids. The last column in this table gives the logarithms of the ratios of the values of for the substituted benzeneboronic acid to the value for ben zeneboronic acid. A simple Hammett plot of the data for meta and para substituents gives considerable scatter with the points for all para-substituents falling above the line for meta-substituents. This is seen in Figure 13. If O' is used 20 , the plot is improved. This is seen in Figure 14. There remains some scatter, but the plot is not improved sig nificantly by modifications of the type suggested by Yakawa 22 23 24 and Tsuno. ’ ’ There is no satisfactory explanation for the very low rate constant observed for m-fluorobenzeneboronic acid. The j o value in Figure 13 is -1.2. This is the 34 + lowest value that has been reported in which a O' correlation is observed for an electrophilic substitution in the benzene ring. Comparison with the reaction in the absence of cadmium ion under the same conditions reveals another striking fact. The y)-value in that case was found to be -2.32. indicating a more discriminating electrophile, but the best cor- 4- relation is given by O', and not O' . It may be concluded that the cadmium ion catalyzed reaction proceeds by a mechanism 33 approaching S*E2 in which localization of -electrons occurs in passage to the transition state III, which has considerable pentadienate cation character and may well pass over into a O'"- complex intermediate. The simple base-catalyzed reaction, on 33 the other hand, appears to proceed by the S*E2 mechanism with a transition state IV, in which there is little disturbance of the 77 -electron system and the positive charge is borne largely by the attacking species, Y, and the leaving species, X. This Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 p-i' 0 i-CIkO Cd - 1.0 - 0.6 -0.3 0 + 0.3 ^-0» A'C varcua cigzia for t.he cadioim'i ion catalysed protodeboronation Cc-u Guo 0:7 nctc c.nd pzi'a sub^titated ber^seneboronic acids at 90*0 degrees. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 •Cl 0.5 - 0.6 =0.3 jOZ k ' /.;-o vcrs'ü.:. .3i[...% ' for the ion catal^'sed protcdeborcnation ■ C . , V . y Ci J ji' r:v. . ant'. :.ra cubotituted bonaeneboro.iic acids at 90.0 degrees. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 transition state passes over into products directly. Since the boronate anion is the substrate in each of the two reactions under consideration, it appears likely that the difference in type of mechanism is due to a difference in the nature of the electrophile. If this inference is correct, the transition state for the rate-determining step of the cad mium ion catalyzed reaction does not involve proton transfer. Ill IV The change from an S*E2 mechanism for the reaction between the boronic acid molecule and a hydronium ion^’^’^*^ to an SE2 mechanism for the reaction between the boronate anion and a water molecule is consistent with the idea that the more polar the carbon-metal bond, the more likely the 33 latter mechanism is to be observed. The differences in linear free energy relationships for the base-catalyzed hydrolysis of areneboronic acids with and without added cad mium ion indicate that a similar change in mechanism can be realized with a given aromatic substrate by an appropriate change in the nature of the electrophile. Below pH 5.80 a pH-independent reaction catalyzed by cadmium ion becomes important. Reuwer^^ has suggested that this reaction might occur by any of three mechanisms; (a) a cadmium ion could be attacking a benzeneboronic acid molecule in the slow step to form an easily hydrolyzed organocadmium Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 compound; (b) a solvated cadmium ion (Cd-OHg)^^ could be donating a proton to the benzeneboronic acid molecule in the slow step; (c) a "cadmium ion-hydronium ion complex" could be donating a proton to the benzeneboronate anion in the slow step. Of these three the latter seems least likely, since it is difficult to visualize a "cadmium ion-hydronium ion complex". A choice between the first two cannot be made with the information at hand. 9. Conclusion. Aromatic protodeboronation may occur by any of four mechanisms in the absence of any metal ions: (a) attack by an acid on a benzeneboronic acid molecule^)9 ; 10 ^ which provides the first kinetic term in equation (34); (b) formation of the benzeneboronate anion in a rapidly established equilibrium, followed by rate- determining attack on this substrate by a water molecule with a specific rate constant given by the following ex pression: ( k ^ ^ - ) ( H 2 0 ^ ) / 5 5 .5 K^; (c) a rate-determining reaction between a water molecule and benzeneboronic acid molecule, in which case the specific rate constant is k^ °; (d) mechanism (c) is kinetically indistinquishable from one in which a hydronium ion reacts with a benzeneboronate anion in the rate-determining step in which case the speci fic rate constant is given by k^ °/55.5 K^. hxp. “ + kon-°(OH-) + (34) The most obvious conclusion to be drawn from the pH-rate profile, seen in Figure 10, is that the base-catalyzed reac tion and the pH-independent reaction are in turn catalyzed by cadmium ion, but that this is probably not true for the acid- catalyzed reaction. In other words, the measured rate coeffi cient in any given experiment, in the presence of cadmium ion. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 will be given by equation (35) or a kinetic equivalent, V ( H + ) + H- k^^o°(H20) + exp, (Cd2+) (35) The presence of corresponding terms for reactions (b) to (d) in the cadmium catalyzed reactions suggests transi tion states of the same composition with a cadmium ion added in each case. Specific rate constants for the various reac ting species have been calculated for 2 ,6 -dimethoxybenzene boronic acid at 90.0°C. and are seen in Table XIV. Included Cd ° in this table are the ratios of k /k , the specific rate constants in the presence and absence of cadmium ion, respec tively . The Ainley-Challenger mechanism for the metal ion- catalyzed protodeboronation above pH 5.80 is favored over the one in which the hydrated metal ion acts as a Brünsted acid for two reasons. In the first place, the normal base-cata lyzed reaction displays a linear free energy correlation with the normal Hammett substituent constant O' , while the cadmium catalyzed-base catalyzed reaction shows a linear free energy 4- correlation with Brown's Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 LO C.O CD o o o •H o r-M r —I r-4 d o ce; X d C X X X X d e d u d Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 halobenzenes and cuprous salts. In the present experiment, this type of reaction could consume only 1% of the boronic acid because of the low initial concentration of copper(II) used. Thus it is likely that the actual catalyst in this case is copper(I) rather than copper (II). As has been mentioned in the previous section, there are three possible mechanisms for the cadmium catalyzed pH- independent reaction which occurs below pH 5.60. With the present data, a choice among these mechanisms cannot be made. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EXPERIMENTAL Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 EXPERIMENTAL Materials 1. Water. The water used in this study was centrally dis tilled water redistilled from Pyrex apparatus used only for that purpose. 2. Areneboronic Acids. All the areneboronic acids used in this work have been described previously. The me^-sub stituted areneboronic acids were prepared according to 35 the method of Bean and Johnson. This method consists of adding the appropriate aryImagnesium bromide to an ether solution of tri-n-butyl borate or trimethyl borate at -70°. The borate ester is then hydrolyzed to the boronic acid with aqueous HgSO^. 2,6-Dimethoxybenzene- boronic acid was prepared in an analogous manner from g the corresponding lithium compound. 3. Malonic Acid. Matheson, Coleman and Bell malonic acid was recrystallized twice from redistilled water. 4. Sodium Hydroxide. The sodium hydroxide solutions used in the preparation of the buffers were made from Fisher Acculute standard solutions diluted with redistilled water. 5. Perchloric Acid. Mallinckrodt 70% perchloric acid was diluted with redistilled water. 6 . Sodium Perchlorate. Fisher sodium perchlorate was re crystallized twice from redistilled water. 7. Metal Salts. The specific metal salts used as addends Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 in the metal ion catalyzed reaction were Fisher reagent grade nitrates of potassium, sodium, lithium, zinc, mag nesium, chromium, lead, copper(ll), and cadmium, and Fisher reagent grade copper(ll) chloride, which were re crystallized twice from redistilled water. Glassware Cleaning Procedure All glassware was cleaned with nitric acid and rinsed fifteen times with ordinary distilled water and four times with re distilled water. pH Measurement All pH measurements were made with a Model R Cambridge pH meter at 25°, employing a saturated calomel reference elec trode and glass indicator electrode. Buffers Stock buffer solutions were prepared by partially neutra lizing the appropriate acid with standard sodium hydroxide solution and diluting to the proper volume with redistilled water. The buffer solutions were stored in polyethylene bottles. Kinetic Procedure 1. Temperature Control. All of the runs were carried out at 90.0°. The constant temperature bath controlled the temperature to within +0.02°. The differential ther mometer in the bath was calibrated against a thermometer standardized at the National Bureau of Standards. 2. Base Catalyzed Hydrolysis. An appropriate amount of the areneboronic acid was weighed out in a paraffin cup and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 then transferred to a 100 ml. volumetric flask. An ali quot from a stock buffer solution was added and the solu tion diluted to the mark with redistilled water. The flask was shaken until all the areneboronic acid had dis solved. Ten ml aliquots of the reaction solution were transferred to ampoules, which were sealed and placed in the constant temperature bath. At measured time inter vals, an ampoule was removed and cooled in an ice-water bath for one minute. The contents were transferred to a volumetric flask containing sufficient HCl to neutralize the buffer base. The volumetric flask was diluted to the mark with redistilled water and the absorbance of the quenched sample measured in a Beckman DU Spectrophotometer. 3. Acid Catalyzed Hydrolysis. The procedure was substan tially the same with the exception that perchloric acid was used to adjust acidity instead of the malonate buffer. Sodium acetate was used in the final dilution procedure to neutralize the perchloric acid. 4. Metal Ion Catalyzed Hydrolysis. The procedure was sub stantially the same as that described above with the ex ception that an aliquot of metal ion was added after the areneboronic acid had dissolved and before dilution. Calculation of Rate Constants The absorbance (A^) of a kinetic sample minus the absorbance of a sample taken at "infinite time" (A ) is directly pro portional to the areneboronic acid concentration in the sample. When log(A^ - A «a ) is plotted versus time, the pseudo first order rate constant can be calculated from the slope by the following equation: ^obs ~ 2.303 x slope. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64 BIBLIOGRAPHY 1. M, F, Lappert, Chem. Rev., 959 (1956). 2. H. G . Kuivila and E. K. Easterbrook, J. Am. Chem. Soc., 73, 123 (I95I). 3. H. G. Kuivila and A. R. Hendrickson, ibid., 74^ 5068 (1952). 4. H. G . Kuivila and E. J. Soboczenski, ibid., 7^^ 2675 (1954). 5. H. G. Kuivila and L. E. Benjamin, ibid., 72, 3834 (1955) . 6 . H. G. Kuivila and R. M. Williams, ibid., 76, 2679 (1954). 7. H. G. Kuivila and T. C. Muller, ibid., 377 (1962). 8 . H. G. Kuivila and K. V. Nahabedian, ibid., 83, 2159 (1961). 9. H. G. Kuivila and K. V. Nahabedian, ibid., 2164 (1961). 10. K. V. Nahabedian and H. G . Kuivila, ibid., H3, 2167 (1961). 11. H. G. Kuivila, ibid., 76, 870 (1954). 12. A. D. Ainley and F . Challenger, J. Chem. Soc., 2171 (1930). 13. A. Michaelis and P. Becker, Ber., 15, 180 (1882). 14. A. Michaelis and M. Behrens, ibid., 27, 244 (1894). 15. J. R. Johnson, M. G . van Campen, Jr., and 0. Grummitt, J. Am. Chem. Soc., 111 (1938). 16. J. F. Reuwer, Ph.D. Thesis, June 1962, University of New Hampshire, Durham, N. H. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 17. R. P. Bell, "Acid-Base Catalysis", pp. 82-85, Oxford University Press, London, 1941. 18. L. P. Hammett, "Physical Organic Chemistry", p. 194, McGraw-Hill, New York, 1956. 19. J. H. Polevy, Ph.D. Thesis, June 1961, University of New Hampshire, Durham, N. H. 20. H. C. Brown and Y . Okamoto, J. Am. Chem. Soc., 79, 1913 (1957). 21. H. Van Bekkum, P. E. Verkade and B. M. Wepster, Rec. trav. chim. , 7_8, 815 (1959). 22. Y . Tsuno, T. Ibata and Y . Yukawa, Bull. Chem. Soc. Japan, 32, 960 (1959). 23. Y . Yukawa and Y. Tsuno, ibid., 32, 965 (1959). 24. Y. Yukawa and Y. Tsuno, ibid. , 32, 971 (1959). 25. R. Heck and S. Winstein, J. Am. Chem. Soc., 79, 3442 (1957). 26. R. Huisgen, J. Witte, H. Walz and W. Jira, Ann., 604, 191 (1957). 27. E. A. Braude and E. S. Stern, J. Chem. Soc., 1096 (1947). 28. H. C. Brown and L. M. Stock, J. Am. Chem. Soc., 3298 (1962). 29. C. Eaborn, J. Chem. Soc., 4858 (1956). 30. C. Eaborn and K. C. Pande, ibid., 297 (1961). 31. C. Eaborn and J. A. Waters, ibid., 542 (1961). 32. C. Eaborn and K. C. Pande, ibid., 3715 (1961). 33. H. Minato, J. C. Ware and T. G . Traylor, J. Am. Chem. Soc., 85, 3024 (1963). 34. J. E. Leffler and E. Grunwald, "Rates and Equilibria of Organic Reactions", John Wiley and Sons, Inc., New York, 1963, p. 208. 35. F. R. Bean and J. R. Johnson, J. Am. Chem. Soc., 4415 (1932). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PART II Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 LIST OF TABLES Number Page I. Spectral data for allyltins in wet methanolj wavelengths used in analytical determina tions...... 74 II. Physical properties and method of synthesis of allyltins...... 77 III. Products of cleavage of cis- and trans- — crotyltrimethyltin with hydrogen chloride in methanol...... 82 IV. Second order rate constants for the hydrogen chloride cleavage of allyltins in 4% water- methanol...... 89 V. Activation parameters for the hydrogen chlo ride cleavage of allyltins in 4% water- methanol...... 93 VI. Comparison of allyltin cleavage with bimolecular nucleophilic substitution...... 102 VII. Effect of added copper (II) ion on the hydrogen chloride cleavage of allyltri- methyltin in 4% water-methanol at 25°...... 104 VIII. Products of cleavage of crotyltrimethyltin with hydrogen chloride in 4% water-methanol 25°, in the presence of copper(II) nitrate...... 106 IX. Effect of added metal ions on the hydrogen chloride cleavage of allyltrimethyltin in 4% water-methanol at 25°...... 108 X. N.M.R. spectra of 1-butene and l-butene-3-d in carbon tetrachloride...... 114 XI. Products of cleavage of cis- and trans- crotyltrimethyltin with deuterium chloride in methanol-d...... 116 XII. Kinetic deuterium isotope effect in the cleavage of allyltins at 25°...... 119 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 LIST OF FIGURES Figure Page 1. Second order rate plot obtained by the aliquot method for the protonolysis of allyltrimethyltin in 4% water-methanol at 0° (Run T-41)...... 90 2. Psuedo-first order rate plot obtained by the direct method for the protonolysis of allyltrimethyltin in 4% water-methanol at 35° (Run T-96)...... 91 3. Psuedo-first order rate plot obtained by the direct method for the deuteronolysis of allyltrimethyltin in 4% deuterium oxide-methanol-d at 25° (Run T-168)...... 92 4. Arrhenius plot of log versus l/T for the protonolysis of allyltrimethyltin...... 94 5. Isokinetic plot of enthalpy of activation versus entropy of activation for the protonolysis of ally 1 trialky It ins...... 99 6 . Petersen plot of log kg/T versus l/T for the protonolysis of allyltrialkyltins...... 100 7. Second order rate constant versus copper(II) concentration for the copper ion catalyzed protonolysis of allyltriethyltin in 4% water-methanol at 25°...... 105 8 . N.M.R. spectrum of l-butene-3-d...... 112 9. N.M.R. spectrum of 1-butene...... 113 10. Plot of isotope rate ratio versus activa tion enthalpy for allyltins at 25°...... 120 11. Potential-energy surface for three-center process with low activation energy...... 123 12. Potential-energy surface for three-center process with high activation energy...... 124 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 INTRODUCTION Electrophilic displacement reactions have commanded considerable attention in recent years. Many of the mechan istic studies of this reaction type have involved cleavages of carbon-metal bonds since metal cations are excellent, leaving groups having low electron affinity. The Croup IV metals have been examined in particular detail. The two most general reactions of the tetra-substituted Croup IV metals are illustrated in equations (I) and (2). R,M + HX ------» R^MX + RH (1) R,M + Xg ------> RgMX + RX (2) I 2 where M silicon , germanium, tin and lead X halogen 3 Eaborn and coworkers have reported an extensive in vestigation of the cleavage of the aryl-metal bond by both halogen acids. The rates of cleavage of substituted aryl- germanium, arylsilicon, aryltin and aryllead derivatives using aryltrialkylmetal compounds as substrates were measured and substituent effects discussed in detail. In these systems, in aqueous ethanolic perchloric acid or sulfuric acid in water-acetic acid, the protonolysis follows a linear free 5 6 energy correlation using the Yukawa-Tsuno equation ’ ’ , log(k/ko) • ( O' + r( - O')) , the value of r steadily decreasing in the order silicon, germanium, tin. for these reactions is positive and it is suggested that the cleavages involve electrophilic attack on carbon. The mono- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 tonic decrease in r indicates that a decreasing amount of positive charge developes in the ring in the transition state and is attributed to an increasing amount of solvent attack on the metal atom. In the reaction of these sub strates in aqueous ethanolic perchloric acid the relative rates of cleavage of the aryl group from the metal are 1:36: 5 8 10 :10 for silicon, germanium, tin and lead, respectively. Because of the unsaturation, attack of electrophilic reagents on a vinyl-metal bond should proceed more readily than attack on an alkyl-metal bond. The vinyl group is re moved from silicon in preference to the methyl group in 7' vinyltrimethylsilane by concentrated sulfuric acid . Milder electrophilic reagents, particularly halogens and halogen acids, usually add to the double bond rather than causing cleavage. With p-styryltrimethylsilane cleavage with bromine g has been reported. Organomercurials, although not members of the Group IV series, display similar behavior when subjected to electro philic cleavage. Pronounced steric and polar effects have 9 been observed by Reutov in the symmetrization of substituted mercuric halides in ammonia, equation (3) COOR nH^ 2 a ) Vi-HgX — (( ) >-Ç-Hs-9-< C ) > (3) The ease of cleavage of the carbon-mercury bond in the reverse reaction has been shown by Dessy^^ to be in the order phenyl> XX alkyl. Dessy and coworkers have also measured the rates of cleavage of a number of dialkyImercurials by acid in water- dioxane solvent. A four-center mechanism, equation (4), which features attack by molecular acid or acid existing as ion pairs Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 on the carbon-mercury bond was proposed. R-Hg-R + HA R-Hg-R -> R-Hg-A + RH (4) À— H A comparison of the cleavage of symmetrical mercurials has shown that unsaturated compounds are cleaved very fast com pared to the saturated compounds. Thus divinylmercury reacts over one hundred times faster than diethylmercury. Organometallic compounds containing an allyl group attached to the metal atom are particularly susceptible to electrophilic cleavage. The allyl group has been shown to cleave in preference to vinyl or phenyl when attached to 12,13 . 14 ^.15 , .16,17 20 silicon , germanium , tin , lead or mercury. Sommer, Tyler and Whitmore 12 have proposed a two-step mecha nism involving the addition of a proton to the terminal position of the allylic group followed by the departure of silicon in a second step to account for the ease of cleavage of allylsilanes by acid, (see equations (5) and (6)). R^Si-CHg-CH-CHg + HA ->■ R^Si-CH^CH-CH. + A (5) R_Si-CHg-CH -CH^ + A^- -> R^SiA + CH^^CH-CH^ (6) Gielen and Nasielski^^ have suggested an SE2' mecha nism for the cleavage of tetraallyltin by iodine primarily on the basis that this compound is cleaved about eight powers of ten more rapidly than tetra-n-propyltin. They represented the cleavage by the mechanism seen in equation (7). R_Sn-CH^-GH=CHg I-1 -> R^Sn + CH^=CH-CH^I + I (7) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 Sleezer, Winstein and Young 20 have reported clearcut evidence for an SE' mechanism in the cleavage of allyImer curials by acid. They observed that crotyl and cinnamyl mer curic derivatives gave as almost exclusive products 1-butene and allylbenzene, respectively. They advanced an SEi' de scription (I) for cleavage in diethyl ether or ethyl acetate. The SE2' path (II) seems consistent with cleavage by per chloric acid in acetic acid. Br-Hg^ Br-Hg ^ Cl^ I CH„ ( CH„ I V 1 2 © s> I 2 H CH H CH H ''R ^ R (I) (II) 21 Recently Kreevoy and coworkers have reported a study of the acid cleavage of allylmercuric iodide in water. They showed that cleavage of crotylmercuric iodide with per chloric acid gave 95% 1-butene and 5% cis-2-butene as gaseous products. The second order rate constant for cleavage of allylmercuric iodide was found to be 0.04 M -1 sec. -1 . The reaction is subject to general acid catalysis and the observed kinetic isotope effect k^/k^ is 3.25. It is clear that k^/k^ measures at least two different kinds of isotope effects and, in fact, is the product of (k^/k^)^, the primary solvent iso tope effect, and (k^/k^)^^, the secondary solvent isotope effect. These two isotope effects could be separated by carrying out the cleavage in various mixtures of partially deuterated solvent. The value of (k^/k^)^ was found to be between 5.1 and 7.3 and that for (k^/k^)^^ between 0.64 and 0.45. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72 22 Kuivila and Verdone have reported a study of the cleavage of allyltin compounds by hydrogen chloride in methanol solvent. The kinetics of the cleavage of six allyl tins in methanol-4% water were measured along with a study 23 of the products of cleavage of crotyltrimethyltin. Verdone has shown that the reaction rate for the cleavage of allyl trimethyltin is dependent on the water content in the metha nol solvent. He also determined salt effects for the reac tion of allyltrimethyltin with both hydrogen chloride and perchloric acid. In the present work these studies on the cleavage of allyltins with acid have been extended to include the fol lowing: (1) seven additional allyltins have been prepared and the rates of cleavage by hydrogen chloride in næthanol- 47o water, at 25°, measured; (2) the effect of temperature on the rate of cleavage of thirteen allyltins was determined and activation parameters calculated; (3) the effect of the addition of certain metal ions on the rate of cleavage of allyltrimethyltin was determined; (4) a study of the products of cleavage of pure cis and trans-crotyltrimethyltin by both hydrogen chloride and deuterium chloride; and (5) a study of the solvent deuterium isotope effect in the cleavage of six allytins. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RESULTS AND DISCUSSION Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 RESULTS AND DISCUSSION I. CLEAVACE OF ALLYTINS WITH HYDROCEN CHLORIDE The kinetics of the cleavage of thirteen allyltins with hydrogen chloride in 4% water-methanol solvent have been 23 studied at 0°,25°, 35° and 45°. Verdone has observed that allyltributyltin shows an unexpectedly strong end absorption in the ultraviolet with a maximum occurring at 215 mu. Similarly, all of the allyltins used in this work exhibit ultraviolet maxima in the region 205 mu to 220 mu. The ultra violet absorption spectra of reactants and products differed sufficiently so that the reactions could be followed by measuring the change in ultraviolet absorption at selected wavelengths. Pertinent spectral data are seen in Table I. The wavelengths used in the analytical determinations were different from since the solvent is not trans parent below 215 mu. The uncertainties in measurement of ex tinction coefficients are small above 220 mu and therefore the wavelengths seen in Table I were chosen. At these wavelengths solutions of the allyltins in methanol showed only a very small negative deviation in Beer's Law in the concentration -4 -5 range 2.00 x 10 M to 1.00 x 10 M. The products of the cleavage reaction showed no absorption at the wavelengths used except in the four cases shown in Table I. Infinity points for these four exceptions were obtained by preparing solutions of known concentration of the reaction products and measuring their absorption at the wavelength used for follow ing the reaction. The values so obtained were subtracted from the absorption of reactants during each kinetic run with these substrates. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74 w w 4J d ü o o u n o o o o o o o o o o o u n o o •H 4J O o 0 0 u n m (Q d CN <*- Ü Ph •H m) 0) e o O o o o o o o o o OO < t I QJ CM O u n vO o 1-4 e n v o e n r-4 CM O MO 4-1 Q r-4 v o vD e n r ^ 00 1^ r-4 00 O d o 00 a \ CM 00 m vD 00 u û o 00 ü cü îH «-4 O •r-l4J (—1 cd < •H jd 4-1 00 (D d CO (U 0 un un un un un un u n u n u n u n u n u n u n :=) 1-4 CM CM CM CM e n CM CM e n CM CM CM CM CM (U CM CM CM CM CM CM CM CM CM CM CM CM CM co > rC cU 4J üO 3 c 0) r(U 4 § 3 OOO O O OO w O MO CM u n OO pq i CM (0^ un 00 Oh o CM o e n e n un Oh 00 r-4 Oh r-4 1-4 t-4 t-4 f: bO U c 0) d Oh O m Lo o CM 00 S T-i 6 OO r-4 1—I I—I r-4 1-4 CM r-4 (U ^ CN Cvi OJ (N CN CMCMCMCM 4J 4J > d eu cfl QJ 3 3 > rL O m d d co • d d • d d c 4-1 • d 4-1 • d r d •H r d 4 J r d 4-1 B 4J d 1—1 r d 1—1 tH • d d - d > . x ; i d o >>. d 4-1 • d 4-1 f : 4 J r d o d • d 1-4 4-1 eu 4-1 eu 4 J r d d • d 4-1 % 1—i B eu B eu •i-i 4-1 %—1 - d O • d B • d e O eu 4-1 r - t > 1 4-1 C: - d d • d d • i4 CM M 4 4 a r-4 > , d (U •r4 4-1 4-1 d 4 J d X O cd •t4 C X • d 4-1 B 4 4 eu I—t 4 J i d 4 J M-1 J4 4 4 •H d . QJ 4-1 (U •i4 r-4 B t—1 [ d 1—1 4 4 r-4 44 o - d 1—l B U X • d d > . d d 1-4 CO 1-4 d o • d 4 4 c d eu d eu d B r O r C d , 1—1 d d r-4 eu 4-1 1 eu 1 eu 4 4 o o eu 4-1 (-H CM 1 CM 1 Q œ 0 ) 44 co > 1 . d 1—1 4 4 A > . 1 CM 1 CM B eu • H ü d , O •i4 I—1 4-1 1 4 J 1 T—i •r4 •i4 •H • d • d 4-1 U d rH d X d , 4 J O cO U S4 d d d O U 4-1 ce) eu eu eu O CM Cl 4 4 4 4 4J 4-1 4-1 d I rH f l d . X i r d O |x l 4-1 r-4 r-4 1—1 r d 1-4 U CO % 4-1 o O O o o X > . % 1 C 4-1 eu 1— 1 r d r d 1—1 5 -2 QJ r-4 r-4 t-4 i-H r-4 co cd O S ü Ü O ü ' d ' A 1-4 1-4 1-4 I—l r-4 • d u d 1 br. r". > d d œ < < < C < o 4 4 o e n CJ a U u * Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 M C o •H 4-1CÜ d) *rHC C •H 4J Q) 4-1 g d) ü -O I—I cO s •dÜ 4-1 d < CO CO d d CO cu S o • d CO • d TO 0) CO CO c 3 CO d 4d 4J 0 0 TO d d cu CO 1—1 X QJ CO CO > • d e cO CO f< 3 Md o o O 4-1 4-4 CU M CO d d d 3 OJ (U 4-4 Md Md X (U (U •d d d 6 X Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 76 1. Synthesis of Allyltins. Two general methods were utilized in the synthesis of the allyltins used in this work. These methods are dexcribed fully in the Experimental section. Method 1 is a modification of that of Jones and coworkers whereby an allyl Grignard reagent is coupled with a trialkyltin chloride in ether solvent. R-CH=C-CH_-MgX + R"Sn-Cl — % --> R_Sn-CH.-C=CH-R + I 2 ° j ether J 2 j R' R' X Mg{^ (7) Cl This method produced very good yields of all the allyltins except the cyclic ones. These cyclic allyltins were pre pared, therefore, by Method 2 which is a modification of the 25 procedure of Kraus and Greer. Trimethyltinsodium was pre pared from trimethyltin chloride and sodium metal in liquid ammonia. This reagent reacted with the cyclic allylic bromide, formed by allylic bromination of the olefin with N-bromo- succinimide, in a nucleophilic displacement reaction to yield product in low yield. R^Sn-Gl + 2Na R^Sn-Na + NaX R-CH=G-CH„-X R.Sn-GH„-C=GH-R I 2 J 2 I R' R' + NaX (8) Table II lists the method of synthesis along with the physical properties of the allyltins used in this work. Since these organotin compounds in general decompose somewhat in air, they were stored in carefully cleaned ampoules under nitrogen. Kinetic samples were purified by gas-liquid chromatography Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 un m o r ^ 1-4 r-4 CM o P4 • 00 r-4 00 r-4 • O CM o O LD o T) 43 o r-4 r-- r-4 r-4 in O 1—1 r- Q) UO MO o r - . CM r-4 0 0 î CM o m un ON r-* MO •H r-4 t-4 1-4 r-4 r-4 4 J OC ü w ü 'H m 4J r4 P h • co CO •HW T) 0) r-4 d) rO rO 4J •r4 en \o CM r-4 1-4 r-4 CM MO MO C >4 00 00 00 00 CM CM >. œ 5-2 CH M O M T3 O 5 U: O 4-J •i4 44 X) ; S d) O rP x: 1—I r-4 CM CM CM CM T3 44 44 g d) •H 44U d) P. O P 3 J-l • 4 3 •t3 3 P h 44 •H 4-1 •H r-4 4-1 r—4 4 J P rH > . rH cd P •H r P >> US >> O •r4 p 44 44 US 4 J US •H 3 44 • 4 1-4 Q) 4 J 3 4 J CO 3 •H 1-4 44 > ) B 3 B 3 •H 4-) 1-4 X Ü • 4 B • 4 B dJ 4-1 rH cd 44 P U •H u •H £ 44 p I—1 > , C 44 r P d) • 4 44 3 44 3 CÜ •1-4 3 % X •i4 d) 44 B 44 i 4 4 J r 4 4-1 U 44 •H P h 3 44 B d) • 4 r 4 X 1—1 > . i 4 44 r-4 + J O X r-4 •H B U P > , P CO t n rH 3 O Î4 •H 44 p Q) 3 P 3 rO X : P h r-4 P 44 S4 r 4 Q) 1 3 3 P 44 u : O Ü CU 1—1 44 ►n r P CM 1 CM 1 CO CU 4-1 cn X r P 1-4 44 P h 1 CM CM B (U •r4 o P h r-4 0 • 4 44 1 44 1 •r4 •H •r4 •i4 •H r-4 44 u Î4 P X P h 4-1 U 3 u u P O CO 44 (U 3 P 3 44 4 J 4 J 44 44 X Î4 1 r 4 P h US r P O 1-4 1—1 rH r-4 1-4 44 CO CO > , O o O O > , t n 1 p 44 i 4 rH r 4 H r-4 r H i-H rH rH CO p 0 u 3 3 3 r-4 1—1 1—1 r-4 1-4 • 4 u S4 > r tH < c c < < < c a O 44 CO U u O U Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 H O 3O ■ •H 4-1 •H 'O Td 3 w3 US3 •rU 3 t H T) O 3 3 US 3 MS g 3 CM •H O cn o 4J US 3 LTl 3 o cn 3 •tU r O C 3 r H 3 r H U M 3 o B 3 3 3 M CO o cn 3 - 3 M T—1 w 3 3 3 •H U S O 3 3 3 U S 3 3 • H MU 3 3 PS B O 3 1—1 * H 3 •H t3 US 3 3 3 U 3 CO cn 3 3 r 4 3 3 4-1 3 3 U S 3 •H X 3 3 CM G •r4 OO 3 BB 3 r H 3 3 • H 3 US P 3 rH H 3 U S 3 4 4 • H cn t3 O US •lU o 3 3 Ph 3 3 T) I—1 • 3 T-4 3 O S S MS 3 ■H •H 4-1 t H • 3 3 Q P S MS S r-U t H 3 X U S B 3 USUS O o 3 3 3 TS I d " H MU 3 3 3 o N N r U t S 3 •H • H t n 3 cn cn US 3 W 3 3 3 •H 3 us U S 3 3 3 3 3 e 4-1 MU C 3 "rH US 3 t H t H 3 O 3 cn cn 3 3 US 3 Td Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79 immediately before use. 2, Reaction System. The allyltins are sufficiently soluble in methanol to allow it to be used as the solvent. 23 Verdone has shown that the rate of cleavage of allyltri methyltin in wet methanol is dependent on the water content. The progressive addition of small amounts of water leads to a large initial decrease in rate. This decrease is uniform to about 0.21% water after which additional amounts of water decreases the rate asymptotically. At 4% water a variation in water content by a factor of ten either way leads to no significant variation in rate. Hence the solvent system em ployed in this work was 4% water-methanol. 23 3. Course of the Reaction. Verdone has shown that allyltributyltin reacts with hydrogen chloride in water- dioxane solvent to yield tributyltin chloride and propylene as evidenced by their infra-red spectra (see equation (10)). But„Sn-CH„-CH-CH„ + HCl — ------> CH„-CH-CH„ + 3 2 2 dioxane-water 2 3 ButgSn-Cl (10) It seems reasonable that a change in solvent from water-dioxane to water-methanol should have no effect on the reaction course, and it is assumed that the products of cleavage of allyltri alkyltins with hydrogen chloride in water-methanol are pro pylene and the trialkyltin chloride. The site of lyonium ion attack may be investigated by examining the olefinic product of cleavage of crotyltrimethyl tin. An SE2 reaction might take place by attack of proton upon the carbon adjacent to the tin atom. Alternatively the attack might occur at the terminal carbon of the allylic triad, i.e. an SE' reaction. Crotyltrimethyltin would yield 2-butene as an SE2 product, while 1-butene would be formed as the BE' Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 product. + Me^ Sn-CHg-CH=CH-CH^ -> Me^Sn + C + H SE2 product + Me„Sn-CH -CH=CH-CH u 2 4[ + u H SE' product To determine the products of cleavage, a solution of hydrogen chloride in methanol was added to a solution of either pure cis- or trans-crotyltrimethyltin in methanol in a closed system. The details of the procedure is given in the Experimental section. After sufficient time had elapsed to allow complete reaction, the gaseous mixture which had been frozen out in a suitable trap, was analyzed by gas-liquid chromatography, using a column of dimethyIsulfolane on fire brick. This column separated 1-butene, cis-2-butene and trans- 2-butene quite cleanly. The number of moles of each component could be determined precisely from the areas in the gas chro- 27 matograms using the method described by Keulemans. All peaks in the gas chromatograms could be accounted for. Along with the butenes, methyl chloride, formed from the reaction of hydrogen chloride with methanol, appears. This compound was identified by comparing its retention time with that of authentic methyl chloride. Although this is not a 23 positive identification, Verdone has observed the same un expected peak in the cleavage of mixtures of cis- and trans- crotyltrimethyltin and has identified it by comparing its infra-red spectrum with a published spectrum of methyl chloride, The major peak in all these runs proved to be due to 1-butene. Smaller amounts of cis- and trans-2-butene were also obtained. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 The results are summarized in Table III. Included in this 23 table are the results of Verdone obtained with mixtures of the two isomers. The formation of 1-butene as the major product in these reactions is indicative that the site of lyonium ion attack is the terminal carbon atom of the allylic group. Confirmatory evidence for this conclusion is presented in Section II, where the cleavage by deuterium chloride is discussed. The most obvious conclusion to be drawn from the fact that 1-butene is accompanied by smaller amounts of cis- and trans-2-butene is that a competing SE2 process attends the main reaction path. Another possible explanation is that the 1-butene is formed initially and isomerizes under the reaction conditions to the 2-butenes. A surprising feature of these results is that the cis isomer always predominates 20 over trans. Sleezer, Winstein and Young and Kreevoy and 21 coworkers have reported similar observations in the acid cleavage of organomercurials. In order to determine whether 1-butene does indeed isomerize under the reaction conditions the following experiment was carried out. A weighed amount of 1-butene was passed into a stirred solution of hydrochlo ric acid in methanol. After 5 min., the system was purged with nitrogen and the butene collected. Gas-liquid chromato graphic analysis showed the presence of both 1-butene and cis- 2-butene. No trans-2-butene was observed. Positive identifi cation was made by comparing the infra-red spectra of these olefins with spectra of authentic samples. The results are seen in item 7 of Table III. The fact that cis2-butene is formed in the isomerization is surprising. The most likely reaction path for the isomerization is protonation of 1-butene at the terminal carbon atom followed by deprotonation of an Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 QJ d m QJ T) W •iH d X 0) Q) CD CD o 1 QJ o 0 Ü o CD T—i CM 1—1 d 0 I—I d cd d x: 1 O u u u u o u M B 4J ■u ■U 4J d d (d cd 0) di Ml •u Mo X) QJ d QJ X •U J-) d •H X QJ (N CM uO 1 r-J I I c O CM I CM O u n u n 00 1 E •S cn u •H rH u >1 rT: u a> QJ d .g QJ u X QJ 00 00 MO m C M u d 1— 1 ON o\ 00 00 en T-4 o X O c 1 E 4J0 x: X Ll 4J S CJ 1 il k m QJ ; d X u n m g •H Ü X d X 00 00 o o m m o H o (N Ovj o o CM CM CM o UJ X QJ o O O d X!- 1 CD u o X E mI •rHo u X X d QJ X o o X CM <}* d o X t—1 QJ m r—i co m o o 00 u n E M) d CM CM o o o X td QJ to X > Ë CD o QJ cd o r-4 'SI X, QJ W o X T— I X B QJ U d d x ^ 2 B ^ B ^ t n o o 0 0 CM u n m c n n - MO O o CM *H n - CM CM r—1 0 0 MO cn O o 0) X X X d Cd 0) X N o u to CO to CO cn 4J QJ X (D d d d d d d Pi X B cd to Cd col cd toi cd to 1 cn l td rO QJ o o u •H u •H w •H u •HX X I E E u CO 4 J a 4 J o | u | u u | u | X o o P h M X cn X X r_| CM cn m VO Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 intermediate carbonium ion. Such a mechanism would un doubtedly form the trans olefin as the major product, since it is more stable. Another possible reaction path is a cyclic concerted process in which proton is transferred and removed in a cyclic six-membered transition state. The formation of cis-2-butene necessitates a cisoid conformation for the transition state (III), while trans-2-butene would result from a transoid conformation (IV). The transoid con formation would be expected to be more energetically favored and cis-2-butene could only be formed from such a transition state if the methyl group rotates close to 180°. Further work is necessary to determine the driving force for this reaction. H CH2- .c " \\ III h '' 0 - MeOH. CH I 3 HCl H $ H CH. -C' \\ C+) .CH. H IV H ■ H CH- > î 3 H 4. Kinetic Procedure. Two kinetic procedures were utilized during the course of this work. For runs carried out at 25°, 35° and 45° a direct spectrophotometrie method was used. The reactions were carried out in a thermostated Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 cell compartment of a Beckman DU spectrophotometer which controlled the temperature to +0.1°. Most of the runs showed good kinetics. However, in the runs at 45° a small upward curvature in the rate plots was observed. This curva ture is presumed to be the result of evaporation of the sol vent and initial rates were used in these runs. For runs at 0° an aliquot method was used. The reactions were carried out in a constant temperature bath controlled to +0.02° and involved removal of an aliquot of the reaction solution at appropriate time intervals and quenching with an aliquot of sodium methoxide in methanol. The absorbance of the sample was then read in a Beckman DU spectrophotometer. It was found that in the latter method readings had to be taken al most immediately since the absorbance of the quenched sample decreased slowly on standing. Apparently a base catalyzed reaction occurs although this matter has not been pursued. Both kinetic procedures are described in the Experimental section. 23 5. Kinetic Treatment. Verdone has shown that the reaction of allyltrialkyltins with hydrogen chloride is second order, first order in acid and first order in allyltin, over a limited extent of reaction. A. Aliquot Method (1) Equal initial concentrations of both reactants. one writes the following for equal initial concen trations of both reactants ; r " ^ 2 1 t o where C concentration of both reactants at zero time, o concentration of both reactants at time, t. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 now the following relationship applies for a spectro scopic method A = Cei (12) where A = absorbance C = concentration (moles/liter) g = extinction coefficient 1 = path length in cm. (1 1.0 in these studies) now the concentration of allyltin in a given aliquot of reaction mixture which has been quenched, C , IS ^ sample-e related to absorbance by. ^sample ^sample (13) £ Now, since the aliquot has been diluted five-fold by the quenching process (see Experimental), the concentration in the reaction mixture, C . , is given by, lOc • mix. Cp . - 5 C - 5 (14) Rx.mxx. sample e when the absorbance at infinite time has a value other than zero a correction must be made, ^sample ^ ^ substituting in eq. (14) gives (\ - A..) (16) or. ^Rx.mix. ^ (A^ - ) (17) substituting eq. (17) in eq. (11) gives, s = kg t (18) 5 (A^ - A _ )^ 5 (A^ - ) o Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86 ^ ^2 ^ (19) (Aj. - A ) ^ (A^ - )^ 6 a plot of -TT T versus time is linear with slope ” OO / 5 kg t (2) Unequal initial concentrations of both reactants. when initial concentrations of reactants are not 28 the same the following equation applies , where a = initial concentration of reactant in excess. b - initial concentration of reactant in limiting amount. X concentration of both a and b that have reacted in time t. X can be converted to concentration directly from absorbance by the following expression, X - C - C - ^ (21) o t ---- ^---- a plot of T (a - x) versus time is linear with slope = k, (a - b) ( r t 2.303 (3) Psuedo first order conditions. when psuedo first order conditions are employed the 28 following equation applies , 2.303 log (a - x) k^ t (22) converting to absorbance through the use of equations (14) and (15) gives, 2.303 log(A(. _ A^ ) - t (23) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 a plot of log (A - A ^ ) versus time is linear with slope h 2.303 is converted to a second order rate constant by- dividing by hydrogen chloride concentration. B . Direct Method (1) Equal initial concentrations of both reactants. in the direct method no dilution terms are present and eq. (19) becomes, _____ 1 1 _ ^2 ^ (24) (A^ - Aoo)j_ (A^ -A )^ & a plot of ______1 versus time is linear with slope kg (^t ^ (2) Unequal initial concentrations of both reactants. no dilution terms present and eq. (21) becomes. X = (25) € rate plot is the same (3) Psuedo first order conditions . all quantities remain the same. Figures 1,2 and 3 show typical rate plots for cleavage of allyltins with hydrogen chloride. 6. Substituent Effects on the Rate of Celavage of 23 Allyltins. Verdone has measured the rates of cleavage of six allyltins with hydrogen chloride in 4% water-methanol at 25°. In the present work seven additional allyltins have been synthesized and their cleavage rates at 25° examined. Since reaction rates are highly dependent on temperature, it was Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 decided to study the effect of temperature on the rate of cleavage of all thirteen substrates. Three additional temperatures were used, 0°, 35° and 45°. Table IV summarized the second order rate constants. These are average values of at least four determinations and are estimated to be precise to 4^ 6%. _ The data presented in Table IV allow the determina tion of the Arrhenius activation energies and entropies for each substrate. This is accomplished using the Arrhenius 28 equation; log k - log A - (AE^/2.303 RT) (26) where A frequency factor E = energy of activation A plot of log k versus l/T is linear with slope = -E /2.303 R. Such a plot is illustrated in Fig. 4, for allyltrimethyltin. The enthalpy and entropy of activation can be calcu lated from equations (27) and (28); $ + AH - AE - RT (27) k - (ekT/h) exp.^^ exp."^^ (28) Table V summarizes the activation parameters for the cleavage of allyltins. The estimated error in energies of activation is + 0.9 kcal./mole, and in entropies of activation +3.2 e.u. Structures (V) and VI) depict the transition state 22 suggested by Kuivila and Verdone for the protonolysis of allyltins. These structures contain as a minimum a lyonium ion and a substrate molecule in which some positive charge has developed on the central carbon atom of the allylic triad. Proton transfer, therefore, has begun and the tin-carbon bond is broken to a substantial degree. Collapse of this structure will lead directly to a heavily solvated cationic tin species. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 cn 0 CT\ m o O cn (U o vO in 00 m ixû in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 üo 30 20 10 9 8 7 6 h 2 1 10 20 30 ho 0 Tlr.'.c, riln"'303 Fig. 1. Second order rato plot oVoained by the aliène b r.cth.od for the protonol%/3ic of el.3.yl'-,rir.ethyltin in '.rater-ncth-anol ,at 0°C, (lîun T-).il). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 1.00 0.90 0.80 0.70 0.60 0.90 o.Uo 0.30 0.20 0.10 0.06 o.oh 2 h 6 3 10 1 o 16 13 Tir.o. rir.ulc" Fig. 2» PsuecTo-first order rate plot obbe.inod Ir; the direct nethod i’or the protonolj’ïîio of oilirltrüidt'r/ltir in vc.tcr-r'.cb'-'.r^'.ol at 39^0, (Run T-96). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 1.00 0.90 0.80 0.70 0.60 0.90 o.ho 0.30 0.20 0.08 0.06 O.Oli 2 11 6 TixiG, mlav'-.oc 3?ig. 3» Psuedo-first order rato plot obt :od b y the dir cob r.cthcd fc: the deutcronolj'sj.s of allj'l'-rir:: cltin in I;y do.vbcriur: c::idc- r.cthanol-d at 29°C. ( T-160 ) ., Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 TABLE V Activation Parameters for the Hydrogen Chloride Cleavage of Allyltins in 4% Water-methanol AE^ ^ AH* a s "*" Substrate kcal. kcal. cal. mole mole mole deg Allyltrimethyltin 14.0 13.4 -13.5 Allyltriethyltin 17.0 16.4 - 3.1 Allyltriisopropyltin 19.1 18.5 + 2.0 Allyltricyclohexyltin 20.3 19.7 + 6.8 Allyltriphenyltin 16.0 15.4 -16.3 cis-Crotyltrimethyltin 15.4 14.8 -13.5 trans-Crotyltrimethyltin 14.4 13.8 -17.9 Crotyltriphenyltin 18.4 17.8 -13.3 p-Methallyltrimethyltin 14.6 14.0 - 3.4 Cyclopent-2-enyltrimethyltin 16.7 16.1 - 7.3 Cyclohex-2-enyltrimethyltin 18.5 17.9 - 4.1 Cyclohept-2-enyltrimethyltin 11.9 11.3 -20.3 Cyclooct-2-enyltrimethyltin 12.8 12.2 -24.9 from least squares analysis of plot of log k« versus l/T Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 2.0 O 0.3 0.2 0.1 0.09 0.06 0.07 3.2 l/T X ICX Fie. 4. Arrhenius plot c f lor k Tcrr.is l / T fer the protor )f r21yl. trii’.Gthyltin in iratcr-r.stin n o l . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 The data presented in Tables IV and V will be discussed in terms of this description. CH. (±) (±) Rg Sn— CH^-rtCR 'nrCHR " fLSn- CR' J ‘ H— OCH. CH-O CHR" I ' H H / / H (V) (VI) A. Structure of the Leaving Group. Conceptually any substituent which can enhance the polarity of structure V or VI in the ground state or in the transition state should enhance the reactivity of a given allyltin substrate. Electron releasing substituents bonded to the tin atom, e.g., R alkyl, should enhance reac tivity while electron withdrawing substituents should dimi nish reactivity. The rate data presented in Table IV show that this is indeed the case. All the sbustrates with elec tron releasing substituents bonded to tin react much faster than allyltriphenyltin. That this difference in reactivity is indeed due to polar factors is seen from a comparison of allyltriphenyltin and allyltricyclohexyltin. In these two cases the steric bulk of the groups are similar, phenyl and cyclohexyl are of comparable size, and the rate difference of over seventy must be attributed to an electronic effect. Polar factors, however, cannot be the sole considera tion as evidenced by a comparison of the first four entries in Table IV. As one varies the alkyl group bonded to the tin atom one would predict the following order of reactivity, corresponding to the degree of inductive electron release; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 cyclohexyl ^ isopropyl > ethyl > methyl. The order found, however, is ethyl > methyl 'p cyclohexyl'^ isopropyl. Apparently other factors are involved. A considerable amount of information is obtained from the enthalpies and entropies of activation seen in Table V, and substituent effects will be discussed in terms of these parameters. The entropy of activation for the cleavage of allyl trimethyltin is -13.5 e.u. This large negative value can be attributed to the following: (1 ) a loss of freedom on going to a single transi tion state from two particles in solution (lyon ium ion and tin substrate). (2 ) a freezing of methanol molecules, presumably around the tin atom, in the transition state. The data in Table V show that as the alkyl group is varied' in the order, methyl, ethyl, isopropyl, cyclohexyl, the en thalpies increase and the entropies become more positive. A 4: 4 plot of AH versus AS for this series is seen in Figure 5. 4= This plot corresponds to a relationship of the form d AH t- P d AS , Where p slope of the line in Figure 5, which has a value of 313°K. Such a relationship has been called an 29 isokinetic relationship or compensating law. The parameter P has the dimensions of absolute temperature and its identified as the actual or virtual temperature at which all the dif- 30 ferences in the rate constants will vanish. Petersen has recently critized the linear relationship between AH and T AS as not being an adequate demonstration of the existence of an isokinetic relationship. He suggests that a true iso kinetic relationship should exhibit a common intersection point when log k/T is plotted versus l/T. Such a plot is shown in Figure 6 for the cleavage of allyltins. Obviously the data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 for this reaction indicates the absence of an isokinetic relationship if Petersen's interpretation is correct. The only conclusion that can be drawn with certainty from Figure 5 is that all members of the series react by the same mecha nism. Any change in mechanism within the series would produce a point significantly deviated from the isokinetic line. If coordination of a methanol molecule with the tin atom from the back side is a significant feature of the transition state then one would expect the enthalpy of acti vation to increase with an increase in the bulk of the alkyl group on tin. This is indeed the case as shown in the data in Table V. Thus allyltricyclohexyltin receives less assis tance from coordinating solvent than allyltrimethyltin and therefore needs a higher activation energy. The trend in entropies is also explained by solvent coordination. The transition state for allyltricyclohexyltin cleavage is less crowded, i.e., less heavily solvated, than that for allyl trimethyltin cleavage and should exhibit a more positive entropy of activation. B . Substitution on the Allyl Group. Substitution of a methyl group for hydrogen at the p-carbon or at the 7 -carbon of allyltrimethyltin gives rise to pronounced differences in reactivity. p-methallyltri- methyltin reacts some fifty times faster than allyltrimethyl tin. This order of reactivity would be expected if stability of the resulting carbonium ion determines reactivity toward protonation. The former compound gives rise to a transition state with tertiary carbonium ion character, while allyltri methyltin gives rise to a transition state with secondary carbonium ion character. As seen in Table V, the reactivity difference is not due to any difference in enthalpy of acti- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 vation since these are similar for the two compounds. The 4: entropies of activation, however, are quite different, AAS being 10 e.u. The more positive entropy of activation for p-methallyltrimethyltin can be attributed to a smaller degree of solvation of the resulting carbonium ion. Since 31 charge dispersal reduces solvation , hyperconjugative structures such as (VII) might be quite important in the transition state of cleavage of p-methallyltrimethyltin. Such structures are not possible with allyltrimethyltin. Me„Sn-CH -C-CH., ^ C - H I H VII The difference in reactivities between allyltri methyltin and the cis- and trans-crotyltrimethyltins, al though small, is unexpected. Allyltrimethyltin is nine times more reactive than cis-crotyltrimethyltin and seven teen times more reactive than the trans isomer. All of these substrates attain secondary carbonium ion character in the transition state and one might expect the /-substi tuted isomers to form the more stable carbonium ion. Com parison of these results with those obtained by Taft and 32 coworkers on the hydration of isobutene and trimethyl- ethylene is instructive. These workers observed that iso butene reacts 1.3 times faster than trimethylethylene. The relatively small effect of structure on reactivities is thought to be due to the compensating larger effects on the enthalpy and entropy of activation. Although the activation energy for hydration of trimethylethylene is larger than that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 a3J.yltrioyclohc:-/-l 19.0 .•hriicoprop;.' % /O, S o,v., Fi^o Iso’-dno-!-,ic plot of cr.t/io.lpp c.? r.otlTo.tic:! vcrcuo entropy o.: activation for the prctcr.clycis of allylt:a:.3 <, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 6»0 2.0 1.0 0.8 0.6 0.2 1 -1 l/r :c 10' 6. Petersen plot of log kg/f " I,r* T T^,\ triollr/ltl'io In cp -;z%or-rz Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 01 for isobutene, the entropy of activation is more positive for the former reaction. There is compelling evidence that in the hydration of olefins a carbonium ion is formed as an intermediate. In the case of the allyltins the activation parameters do not compensate each other. The activation energies are larger for the /-substituted isomers while the entropy of activation is more positive for allyltrimethyltin. It can be concluded that in the cleavage of allyltins the reaction probably proceeds by more of a concerted process rather than a two-step mechanism similar to that proposed by 12 Sommer, Tyler and Whitmore in the cleavage of allyltrimethyl- silane. C. Cyclic Allyltins. When the double bond of allyltins is incorporated into a ring pronounced changes in reactivity are observed with ring size. Data for the common rings (five- to seven- membered) results in an order of reactivity: 7 > 8 ^ 5 > 6 . Ideally one would like to be able to correlate this data with data for other electrophilic substitutions. To this author's knowledge no such data are available in the litera ture. Data are available, however, for bimolecular nucleo- philic displacement of cycloalkyl bromides with lithium 33 iodide , a reaction which involves a hybridization change 3 2 from sp to sp . These data are seen in Table VI along with data for the protonolysis of allyltins, normalized using allyltrimethyltin as 1 .0 0 . In the reaction of cycloalkyl bromides with lithium 33 iodide , the six-membered ring is slow. The reason given for this is that the chair form in the ground state is free of bond oppositions. A change in coordination number from 4 to 5 incurred in the transition state engenders bond Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 TABLE V I Comparison of Allyltin Cleavage with Bimolecular Nucleo- philic Substitution (SN2) Rel. Rate of the Rel. Rate of dis- protonolysis of placement of cyclo- Ring Size cyclic allyltins alkyl bromides a acyclic 1 .0 0 ^ 1.00 5 0.24 1.2 6 0.057 0.015 7 0.98 0.79 8 0.25 0.14 ^ see ref. 34 ^ allyltrimethyltin taken as 1 .00 oppositions and is, therefore, resisted. The five- and seven- membered rings are beset with bond oppositions in the ground state which are relieved in going to the transition state and thus are more reactive. The eight-membered ring is beset with angle deformations, bond opposition and transannular interactions, most of which are due to hydrogen-hydrogen 2 interaction, which are relieved in going to an sp transition state. Therefore, the eight-membered ring should also react faster than the six-membered ring. In the protonolysis of allyltins, cyclohex-2-enyltri- 2 methyltin possesses two carbon atoms with sp hybridization Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 in the ground state. In the transition state a third carbon atom attains planar character and should be resisted accord ing to the above concepts. The data in Table VI shows that H >— Sn(CH^)^------® \ --- SnMe^ cyclohex-2 -enyltrimethyltin does indeed react more slowly than the other members of the series. The data for the seven- and eight-membered rings in this series agree quite well with the data for bimolecular nucleophilic substitution; however, the five-membered ring falls completely out of line. The data in Table V indicates that the lowered reactivity is due primarily to a high activation enthalpy. This might well be expected since the allylic carbonium ion type character pro duced in the transition state introduces considerable angle strain in the five-membered ring and should be resisted. The angle strain produced in the transition state of the seven- and eight-membered rings is certainly not as great, and these substrates should have lowered enthalpies of activation, as was observed. 23 7. Effect of Added Metal Ions. Verdone has re ported that the addition of a small amount of cadmium(II) nitrate greatly accelerated the rate of the hydrogen chloride cleavage of allyltrimethyltin. The possibility that cadmium ion and metal ions in general could effectively cleave allyl tins to form intermediate allylmetals proved quite intriguing and a complete study of the effects of metal ions on the pro tonolysis of allyltins was undertaken. Table VII summarizes the results obtained using copper(II) , as addend. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 TABLE V I I Effect of Added Copper(II) Ion on the Hydrogen Chloride Cleavage of Allyltriethyltin in 4% Water-methanol at 25° a k ^ cat Copper(II) Gone. -1 -1 _2 _q Run (moles/liter) M sec. M sec. T-66 1. 0 0 X 1 0 "^ 0.761 1.58 X 1 0 ^ T-70 2 . 0 0 X 1 0 "^ 0.840 1 . 2 0 X 1 0 ^ T- 6 I 1 0 . 0 X 1 0 "^ 1.87 1.27 X 1q5 T-69 2 0 . 0 X 1 0 "^ 3.75 1.58 X 1 0 ^ T-65 50.0 X 10"^ too fast control none 0.603 ^ obtained from the following equation: k 0.603 cat (copper conc.) ^ Allyltriethyltin 0.935 x 10 HCl 1.460 X 10“^M As can be seen from the data in Table VII, the ad dition of trace amounts of copper(II) ion greatly accelerated the cleavage of allyltriethyltin. A plot of the second order rate constant, k^, versus copper(II) concentration is seen in Figure 7. This plot illustrates that the dependence of second order rate constant on copper(II) concentration is linear. In order to be sure that the reaction which was being studied was the same as that in the absence of any copper(II) ion, the products of the cleavage had to be examined. To this end crotyltriethyltin was synthesized and the products of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 2.6 2 .1 cc 1.8 l.li 1.0 3.0 r 0 or(lr) CO: Fig. 7o Second order rnto :er(concentre - *T *1 — .*1 (• •* »*> copper ion cr:':,?.ly2 /■' .'^"1 * e' :_n ncl’r3.nol at 23 C. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 cleavage examined. The results are seen in Table VIII. TABLE VIII Products of the Cleavage of Crotyltriethyltin with Hydrogen Chloride in 4% Water-methanol at 25°, in the Presence of Copper(II) Nitrate^ Product mole % 1-Butene 77.5 cis-2-Butene 10.8 trans-2-Butene 1.6 Unidentified 10.1 ^ Crotyltriethyltin: 0.27M (47% cis, 53% trans) Hydrochloric Acid: 0.31M Copper(II) Nitrate: 0.27M Four gaseous products were obtained in the cleavage reaction. The main product proved to be 1-butene, accompanied by smaller amounts of cis- and trans-2-butene. Thus, the course of the reaction is essentially the same as that in the absence of added copper(II) ion. An additional gaseous pro duct was obtained, which had a retention time in the G.L.C. chromatogram similar to that for the 2-butenes. This pro duct accounted for 1 0 % of the product mixture and was not identified. In addition to the gaseous products, 0.198 g. of a grey-white solid was also obtained. X-ray diffraction analy sis of this compound showed it to have the same powder pattern Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 as copper(I) chloride. At this time I would like to thank Dr, H. M. Haendler for determining the x-ray powder pattern. Apparently, cupric ion is reduced during the reaction to cuprous ion, which precipitates as the insoluble chloride in the presence of chloride ion. The linear rate increase with increasing copper(II) ion, along with the observation that this ion is reduced during the reaction, is indicative that the following process takes place: iySn-CH.-CH=CHg + 2CuCl, RgSnCl + (CuCl)2 + CH2 =CH-CH2 C1 (29) R_Sn-CH_-CH=CH_ + (CuCl)^. .R^SnCl + CH^-CH-CH Cu (30) CH^-CH-CH^Cu + (31) The effect of a number of other metal ions on the rate of protonolysis of allyltins has also been examined. The results are presented in Table IX. When cadmium and zinc nitrates were used as addends, a rate decrease is seen with increasing metal ion concentration. This decrease is not linear and appears to approach a minimum value when stoichioiætrie amounts of addend are present. This rate decrease is not due to any change in acidity of the solu tions since control experiments showed that no change in pH results from the addition of the metal ions. These results are opposite to those seen with--copper(II) as addend and are difficult to interpret. One possibility is that the added metal ion complexes with the allyltin in some unknown manner. This complex might be expected to be less susceptible to electrophilic attack than the uncomplèxed substrate. At low metal ion concentration the amount of "complex" is small and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 108 TABLE IX Effect of Added Metal Ions on the Hydrogen Chloride Cleavage of AllyItrimethyItin in 4% Water-methanol at 25° ^ Metal Ion Cone, M-1 2 -1 Metal Ion (moles/liter) M sec. control none 0.475 cadmium 1.00 X 1 0 “^ 0.460 c admium 2.50 X 10-= 0.420 cadmium 5.00 X 1 0 "^ 0.319 cadmium 7.50 X 10-5 0.328 cadmium 10.0 X 10"5 0.322 cadmium 20 . 0 X 10"5 0.272 cadmium 50.0 X 10"5 0.300 zinc(II) 1.00 X 10"5 0.446 zinc(II) 2.50 X 10"5 0.462 zinc(II) 5.00 X 10-5 0.415 zinc(II) 7.50 X 10-5 0.415 zinc(II) 10.0 X 10-5 0.430 zinc(II) 20 .0 X 10-5 0.389 zinc(II) 50.0 X 10-5 0.345 lead(II) 1.00 X 10-5 0.496 lead (II) 5.00 X 10-5 0.516 b silver 1.00 X 10-5 0.452 silver 5.00 X 10-5 0.455 • 1 b silver 10.0 X 10-5 0.452 -4. Allyltrimethyltin: 1.159 x 10 M HCl 7.500 X l O ' ^ M perchloric acid used instead of hydrochloric acid Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 109 only a small rate decrease would be observed. As the metal ion concentration approaches the stoichiometric concentra tion of allyltin the amount of "complex" would approach a maximum and the rate decrease a minimum. This type of situation is illustrated in equations (32-34) where > kg'. RgSn-CHg-CH^CHg + ---- > (R Sn-CHg-CH^CHg :M^"^) (32) RgSn-CHg-CH-CHg + i P ^2. ^ R ^ S n ® + GHg-CH-CH^ (33) (RgSn-CHg-CH-CHg :M^"^) + h'*' ■■,.^2..'___^ R^Sn® + (34) CHg-CH-CHg + When silver nitrate was used as addend, the second order rate constant was the same as that in the absence of any addend, within experimental error. Product analysis with silver ion produced no isolable gases but did result in the isolation of two different solids. These two solids were identified as silver metal, from reduction of silver ion under the reaction conditions, and trimethyltin nitrate monohydrate. This latter product was identified by com paring its melting point with that reported by Yasuda and 35 Okawara . The results with silver ion are surprising, since van der Kirk and coworkers^^ have reported that this species effectively cleaves phenyl groups in a variety of phenyl substituted tin compounds. Apparently the protonolysis of allyltins proceeds much faster than cleavage by silver ion, and no effect of added silver ion is observed kinetically. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 110 II. CLEAVAGE OF ALLYLTINS WITH DEUTERIUM CHLORIDE The kinetics of the cleavage of six allyltins with deuterium chloride in 4% deuterium oxide-methanol-d solvent have been examined at 25°. The kinetic procedure was the same as that used to study the hydrogen chloride reaction. All runs showed good psuedo first order kinetics. Also effected was an analysis of the products of the cleavage of cis- and trans-crotyltrimethyltin with deuterium chloride. Product analysis was similar to that used in the hydrogen chloride reaction and is described fully in the Experimental section. 1. Starting Materials. The allyltins used in this study were prepared by the same methods as those described in Section 1. Deuterium chloride was conveniently prepared 37 by the method of Brown and Groot. This method involved the hydrolysis of benzoyl chloride with deuterium oxide. In order to observe maximum kinetic isotope effects it is necessary to work with solvents of high isotopic purity. 38 Streitweiser and coworkers have recently reported an ex cellent method for the preparation of methanol-d. Utiliza tion of this method which involves the hydrolysis of di- methylcarbonate with deuterium oxide using a dimethylsulfate catalyst afforded methanol-d containing from 9 6 % to 98% deuterium as determined by infra-red analysis. Details are presented in the Experimental section. 2. Course of the Reaction. In the work reported in Section I, the site of lyonium ion attack was investigated by examining the olefinic products produced in the cleavage of the isomeric crotyltrimethyltins with hydrogen chloride. The fact that 1-butene is formed as the major product indi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I l l cates that an SE' process is the major pathway, but does not necessitate this conclusion. Confirmatory evidence, however, could be obtained by carrying out the cleavage with deuterium chloride and examining the olefin produced for the position of deuterium incorporation. If attack is at the terminal position of the allylic group, the n.m.r. spectrum should show deuteration at the 3-position of the 1 - butene produced. To this end, a mixture of cis- and trans- crotyltrimethyltin was subjected to cleavage with deuterium chloride in methanol-d and the butenes collected. The gases were distilled into an n.m.r. tube and dissolved in carbon tetrachloride. Figure 8 reproduces the n.m.r. spectrum of the product so obtained. For comparison purposes an n.m.r. spectrum of authentic 1-butene is seen in Figure 9. Comparison of Figures 8 and 9 shows that the two spectra are similar. The observed differences are com pletely consistent with the conclusion that deuteration has occurred at the 3-position. The methyl group is a well de fined triplet appearing at 8.74 7^ in authentic 1-butene. In the deuterated compound this triplet has been reduced to a doublet appearing at 8.80 7" . This is what is expected if deuterium has been incorporated in the 3-position. Similarly, the vinyl proton in the 2 -position of 1 -butene, appearing at 3.90 7“ , is a multiplet of twelve lines. The deuterated compound shows vinyl proton absorption at 3.95 and is a multiplet of eight lines. The methylene protons of 1-butene are a multiplet of twenty-four lines which appear at 7.72 7" . The corresponding methine proton in the deuterated compound appears at 7.75 and is a poorly defined multiplet which could not be analyzed. The singlet appearing at 6.60 7" in Figure 8 is due to the methyl group of methanol-d which was mechanically transferred to the n.m.r. tube during distilla- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 a H O 13 - b • - 1 O '-a •H r-i o r4 O •P O o r~i f-: Ci o I m i oa -p ! 'ci r- p H C cH o \ ; o li o I -;?> / \ o Ci o wPh o Pi o o CO ?» 'H1 x 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 ON Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 4 tion. A summary of the spectra is seen in Table X. TABLE X N.M.R. Spectra of 1-Butene and l-Butene-3-d in Carbon Tetra chloride Spectrum No. 724 Authentic 1-butene (b) H H (c) C = C / \ H CH CH. (a) 2 ""3 (d) (e) Protons Value Multiplicity Coupling Constants a 4.77 12 J, ^ 9.8 c.p.s. b-c b 5.00 4 J = 17.6 c.p.s. a-c ^ c 3.90 12 ^ ^ 6 . 0 c.p.s. 7.72 24 J d a-b e 8.74 3 Spectrum No. 725 (b) H H H CHD - CH (a) (d) (&) Protons Value Multiplicity Coupling Constants a 4.72 b 4.92 c 3.95 not analyzed d 7.75 not resolved e 8.80 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 115 Analysis of the products of the cleavage of cis- and trans-crotyltrimethyltin with deuterium chloride in methanol-d. using the technique described in Section I, afforded the re sults seen in Table XI. In all the experiments seen in Table XI, the major product of cleavage is 1-butene. This result is similar to that observed in the hydrogen chloride reaction. In the cleavage of mixtures of the isomeric crotyltins with DCl the amount of cis-2 -butene accompanying 1 -butene is comparable to the amount obtained with HCl. When either pure cis- or pure trans-crotyltrimethyltin was cleaved with DCl, items 3 and 4 in Table X, a much larger amount of cis-2-butene was observed. In these two cases the concentration of DCl is much larger than the initial concentration of crotyltin and one would expect a larger amount of cis-2 -butene if isomeri zation of 1-butene leads to this product. The result of an isomerization experiment carried out in a manner similar to that described in Section 1, using DCl in methanol-d instead of HCl in methanol, is seen in item 5 of Table XI. 1-Butene isomerized to a mixture containing 26% cis-2-butene. This figure cannot rigorously be compared with the 8 % obtained with HCl since these values do not represent an equilibrium mixture. The experimental procedure did not lend itself to the determination of an equilibrium value. Further work is necessary in order to clarify the significance of these ex periments . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 116 CD d CD P S'S d 0) CD CD X CD ü ü CJ o CD 1 P cd cd cd cd d CM o u p p o 1 B 4J p p d cn d cd p p d 'H P CD rH d CD jd p p d QJ X CD O v D e 1 t—1 en CvJ •H CM o P X) 1 B P 1 cn tP r-4 •rH >, o o P d O cd P X i a p 1 CD CD cn S d d CD cd d p CD in o o <*• p •rH d r—1 en en p rd o hH CD 1 B X -d Td p d •H w Cd P O pq 1 1—1 CNJ en LO Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 117 3. Kinetic Deuterium Isotope Effect. Three factors contribute to the generally lower reactivity of bonds to deuterium as compared to the corresponding bonds to hydrogen. These are the differences in free energy, the effect of the difference in mass on the velocity of passage over the potential-energy barrier, and the possibility of non-classi- 39 cal penetration of the energy barrier. The major factor that contributes to the free energy difference is the dif ference in zero-point energy between a bond to deuterium and the corresponding bond to hydrogen. The maximum isotope effect will be obtained when the bond to hydrogen or deuter ium is essentially completely cleaved in the activated com plex, and the isotope effect will decrease with increasing bonding in the activated complex. In order to obtain more information concerning the structure of the transition state in the protonolysis of allyltins it was decided to measure the kinetic deuterium isotope effect. The rates of cleavage of six allyltins with deuterium chloride in 4% deuterium oxide-methanol-d at 25“ have been studied. The kinetic procedures were the same as those used to study the hydrogen chloride reaction. Second order rate constants are summarized in Table XII. These are average values of at least two determinations and are estimated to be precise to + 6 %. Included in this table are the second order rate constants for the hydrogen chloride reaction. The ob served kinetic deuterium isotope effect is obtained by divi- , H . , D ding k„ by k„ . HD The observed kinetic deuterium isotope effect, kg/kg, for allyltrimethyltin, as seen in Table XII, is 3.27. The magnitude of this "normal" isotope rate ratio is consistent with the idea that proton or deuteron is transferred in the rate-determining step of the reaction. Such a transfer is implicit in the description of the transition state proposed Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1X8 22 by Kuivila and Verdone for the protonolysis of allyltins. One must be careful in drawing conclusions from the measure ment of one isotope effect alone, however, and it would be advantageous to separate the measured isotope effect into primary and secondary effects. Kreevoy and coworkers 21 have been able to distinguish these effects in the perchloric acid cleavage of allylmercuric iodide in water. The measured iso top rate ratio for this reaction was 3.25. This observed isotope effect was separated into a primary effect having a value between 5.1 and 7.3 and a secondary effect having a value between 0.64 and 0.45. The system in the present work is not amenable to the separation of these effects. Water is the solvent of choice in such work, whereas the protonolysis of allyltins has been carried out in aqueous methanol. In the study of isotope effects a great deal of in formation regarding the transition state can be obtained by the elucidation of the parameters which influence the measured isotope rate ratio. These include the effects of solvent, temperature and catalysts. In the present work a study of the effect of variation in structure of the allyltin on the measured isotope rate ratio has been made. Table XII shows that the kinetic deuterium isotope effect indeed varies quite significantly with the structure of the allyltin. kg/kg is 5.11 for allyltricyclohexyltin and only 2.40 for cyclooct-2- enyltrimethyltin. Similarly the isotope rate ratios for the other substrates are all different. It is immediately obvious that the trend in isotope effect is directly related to the activation energies obtained from Table V. Figure 10 shows a plot of kg/kg versus activation enthalpy. The linear relation ship seen in this plot is at first surprising. The general expression for the hydrogen isotope effect, equation (35) con tains no term for activation energy and would predict that the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 119 Q CM T—1 00 CN O CNJ cn rH rH VO CO cn m (N CsJ w c •H 4-» t—I rH O <1- 0) LO < t rH rH LOLO CO r-s o tH VO I—1 tH o cn rH < t 1-4 1 O o o o o O o 0) X CN cd> QJ t—I o eu î-4 I Ü CN QJ cn 00 r^ iH •S cn rH VJD o 00 1—4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120 0 cyclop ont-2-cnylirij kcal r.ôiô 12,0 cycl 3-0 luO k 2 2 Fly, 10, ELot of isotope rate ro.tio vor--.: at 2p C. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 121 isotope rate ratio should not be affected by this parameter. — '< f ) - f X - i Z l i 3 yn “7 ^ y .5xh-(3 ^ frfrWl TT i « It is generally recognized, however, that in a three-center process the isotope effect increases in the same sequence as that in which the activation energy becomes larger. The reason for this is clear. In most three-center reactions the stretching of the bond to be finally broken makes a con siderable contribution to the activation energy. It is to be expected that a process with low activation energy reaches the transition state early along the reaction coordinate. This means that in the case of the protonolysis of allyltins the oxygen-hydrogen bond of the proton being transferred from lyonium ion has been stretched very little. The transition state will resemble reactants and the initial oxygen-hydrogen bond will possess a good deal of its zero-point energy. Figure 11 reproduces the type of potential-energy surface 40 approximating this situation. In this figure the transition state corresponds to the same hydrogen-oxygen distance as in the reactants and the reaction path is still parallel to the axis r^ In a process with a higher activation energy it is expected that the fission of the oxygen-hydrogen bond will be Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 122 greater since the transition state is reached further along the reaction coordinate. Figure 12 would better approximate this situation. It is quite obvious that Figure 11, the lower energy path, would predict a lower isotope effect. The above considerations must be used with care, however, since the relationship between activation energy and isotope effect is strictly empirical. In Figure 10, the point for cyclopent-2 -enyltrimethyltin deviates considerably from the line. The isotope rate ration is definitely not in line with the activation enthalpy for this substrate. It may well be that this substrate reacts by a different mecha nism; however, this possibility has not been tested. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 123 Fi-Z» 11* Potential encre:' rarPaco for thrco-contcrcd procecs --ith loi: o.ctiaT.tion onorr:'. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 124 F4"» l2 . Potential onorc:/ cnriao: 1er three-c:ntc:.'cl n: hinh activation cn.c.vrr'j Reproduced with permission of the copyright owner. Further reproduction prohibitedpermission. without 125 I I I . MECHANISM There are a number of mechanistic possibilities for the protonolysis of allyltins. The amount of data accumulated so far enables one to critically discard some of these; how ever, at least two alternatives remain. In the discussion be low possible mechanisms are presented and criticized in light of the experimental results. A rather unlikely mechanism that might be operative in the system used in these experiments is one in which the allyltin ionizes in a rate-determining step, which is followed by a rapid proton transfer to the allylcarbanion. This pro cess which is SEl in character is illustrated in equations (36-37). If such a mechanism was operative first order R^Sn-CHg-CH-CHg R^Sn + CH^-CH-CH^ (36) CHg-CH-CHg + H > CH^-CH-CHg (37) kinetics would be obeyed and no kinetic deuterium isotope 23 effect would be observed. Verdone has shown that the pro tonolysis of allyltins is second order, first order in allyl tin substrate and first order in acid. This result coupled with the observation of a large "normal"kinetic deuterium isotope effect eliminates this possibility. A second mechanistic path is one in which a rate- determining proton transfer takes place at the carbon atom bonded directly to the tin atom. This SE2 mechanism is illus trated in equation (38). A bimolecular substitution mechanism is consistent with the observed kinetics, but does not agree ® Ab R„ Sn-CH„-CH=CHR + H --: > R-Sn + CH„-CH=CHR (38) 3 2 slow 3 3 ^ ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 126 with the observed products of the reaction. Cleavage of cis- and trans-crotyltrimethyltin with either hydrogen chloride or deuterium chloride produces 1 -butene as the major product. One might argue that the observation of a rearranged olefin does not necessarily rule out the possibility of direct cleavage of the carbon-tin bond since the 1 -butene may have been formed from isomerization of an initially formed 2 -butene. The experiment with deuterium chloride, however, eliminates such an isomerization. Analysis of the n.m.r. splitting pat terns of the 1 -butene formed from reaction of the isomeric crotyltins with DCl indicates that deuterium is present only in the 3-position of the olefin. If isomerization had oc curred deuterium would also be present in the 1 -position. A bimolecular mechanism that would permit rearrange ment is seen in equations (39-40). This mechanism involves a pre-equilibrium between allyltin and hydrogen ion followed by a rate-determining collapse of this species to products. (lb R„Sn-CH„-CH-CH„ + H R„ SnCH„CH-CH„ (39) J z z fast J z j R.]SnCH_CH-CHg — :--- > R_Sn + CH.-CHCH. (40) 3 2 3 slow 3 Z 3 41 It is generally accepted that reactions which proceed by a pre-equilibrium proton transfer mechanism will have an isotope rate ratio, k^/k^, less than unity. It has also been shown that mechanisms which proceed by rate-determining proton trans fers have k^/k^ values of, or greater than, unity.The ob served isotope rate ratio for allyltrimethyltin is 3.27. This observation clearly rules out a pre-equilibrium mechanism. Supporting evidence for this conclusion is found in the reac tion of the isomeric crotyltins with DCl. A pre-equilibrium necessitates that more than one deuterium atom should appear in the olefinic product. The n.m.r. splitting patterns de- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 127 scribed elsewhere for the 1 -butene produced indicates that only one deuterium has been incorporated. The above considerations leave us with two alternate mechanisms which are consistent with the experimental results The first of these is a concerted proton transfer to the terminal position of the allylic triad yielding products directly. The second is a two-step process involving rate- determining proton transfer to the terminal carbon atom of the allylic group in the first step followed by the collapse of the intermediate carbonium ion to products in a rapid second step. Both processes are SE’ and are illustrated in equations (41) and (42-43). Concerted process C±) A RgSn-CHg-CH-CHg + H slow RgSn + CH^-CH-CH^ (41) Two-step process R^Sn-CHg-CH-CH^ + H (42) slow ELSnCHgCH-CH. © - — — ^ R.Sn + CH_ :CH-CH_ (43) R^SnCHgCH-CH^ ---fast 3 2 3 These two mechanisms are kinetically indistinguish able. Both are completely consistent with the available data and it may well be that the true reaction path lies somewhere in between. By proper choice of substituents one could, in theory, favor one or the other of these mechanisms. For example, if stability of the resulting carbonium ion is a factor in determining reactivity then one would expect a large rate difference between allyltrimethyltin and (3-methal- lyltrimethyltin as was observed. Allyltrimethyltin forms a secondary carbonium ion on protonation while p-methallyltfi- methyltin forms a tertiary one. The rate difference is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 128 T largely due to entropy, M S being îîr 10 e.u. in favor of p- methallyltrimethyltin. It may well be that p-methallyltri methyltin proceeds by more of a two-step process than allyl trimethyltin. The differences in the two mechanisms are very subtle and it is difficult to choose between them on kinetic grounds. It is probably more fruitful if the experimental data were used instead to describe the transition state. Structures (VIII) and (IX) represent a modification 22 of the transition state proposed by Kuivila and Verdone for the protonolysis of allyltins. Structure (VIII) represents R R \ f C H g O Sn — . CH_ ■J I / Z © ' z ' VIII H— 0 CH., H R R ,CH_ CH. I " Z - - - ' C H „ 0 Sn" ' © '''CH. IX ,0 H y\ CH3 H an SE2' transition state while structure (IX) represents an SEi' transition state. The differences between these are slight. The major distinction being one of geometry rather than energetics. The energy of the two structures should be similar. The SEi' transition state stipulates that proton transfer takes place from lyonium ion which is coordinated with the tin atom and possesses a cyclic geometry. It is quite certain that lyonium ion is attacking species rather 23 than molecular acid. Both structures predict a large kin etic isotope effect. An important feature of both these structures is coordination of a solvent molecule from the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 129 backside of the tin atom assisting the departure of the + RgSn function. This conclusion arises from the observation of linear effects in activation parameters as the steric bulk of the R group is increased. If it is assumed that variation in the structure of the R group has no effect, aside from a small inductive effect, on the proton transfer, the large entropy changes must be due to steric interference of the solvent molecule that is assisting carbon-tin cleavage. In connection with the cyclic allyltins it is most likely that structure (VIII) is more nearly correct since the cyclic structure (IX) would be less favored energetically. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EXPERIMENTAL Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 130 EXPERIMENTAL I. MATERIALS 1. Organotin Substrates. All the allyltins used in this work were synthesized by either one or the other of the methods described below. Method I In a 500 ml. three-necked round bottom flask equipped with stirrer, condenser and pressure equalizing addition funnel was placed 0.75 g-atoms of magnesium and 100 ml. an hydrous ether. A small crystal of iodine was added along with a small amount of the appropriate allyl chloride. The reaction was started by warming the stirred solution slightly. The appropriate allyl chloride (0.25 mole) was then added drop- wise over a two-hour period. A.cter addition was complete the reaction mixture was stirred for an additional one hour. The allyl Grignard reagent was then transferred to a 1000 ml. three-necked round bottom flask by filtering the mixture through glass wool. The flask was fitted with a stirrer, con denser and pressure equalizing addition funnel and 0.25 mole of the appropriate trialkyltin chloride in 100 ml. anhydrous ether was added over a one-hour period. After addition was complete the stirred solution was refluxed for an additional one hour. The mixture was then cooled to 0°, and hydrolyzed with 25% ammonium chloride solution. The ether layer was separated and dried over anhydrous magnesium sulfate. The magnesium sulfate was removed by filtration and the ether evaporated on a rotary evaporator. The product was then dis tilled under reduced pressure. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 131 Method II In a 1000 ml. three-necked round bottom flask fitted with a Cole-Palmer stir-o-vac high speed stirrer, Dewar con denser cooled to -70° and pressure equalizing addition fun nel was placed 300 ml. ammonia. The reaction flask was main tained at -70° during this addition of ammonia. Trialkyltin chloride (0.25 mole) was then added and the reaction stirred quite vigorously. Sodium (0.50 g-atoms) was then added in small pieces over about a three-hour period. At the end point a deep blue color characteristic of sodium in ammonia persisted for at least ten minutes. At this point small quantities of trialkyltin chloride were then added until the color changed from deep blue to a yellow-orange characteris tic of trialkyltin sodium. The appropriate allyl chloride (or bromide) (p. 25 mole) in a small amount of ether was then added dropwise over a one-hour period. After addition was complete, 250 ml. of anhydrous ether was added and the ammonia evaporated. Water was then added to dissolve salts and wash out any trialkyltin chloride. The ether layer was separated and dried over anhydrous magnesium sulfate. The magnesium sulfate was removed by filtration and the ether evaporated on a rotary evaporator. The product was then dis tilled under reduced pressure. Since organotin compounds in general decompose some what in air all the allyltins were stored in carefully cleaned glass ampoules under nitrogen. Kinetic samples were purified by gas-liquid chromatography using a 20 ft. column of General Electric XF 1150 silicone nitrile (17%) on Chromosorb P (40- ôOmesh) immediately before use. Allyltrimethyltin was synthesized from allylchloride and trimethyltin chloride by Method I in 73% yield, b.p. 126-128°. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 132 Analysis: Calculated for C^H^^Sn: G, 35.17; H, 6.89. Found: G, 35.27; H, 6.85 Allyltriethyltin was synthesized from allyl chloride and triethyltin chloride by Method I in 76% yield, b.p. 76- 77°/lO mm. Analysis: Calculated for CgHg^Sn: G, 43.90; H, 7.72. Found: C, 44.11; H, 7.94. Allyltriisopropyltin was synthesized from allyl chlo ride and triisopropyltin chloride by Method I in 82% yield, b.p. 100-101°/7 mm. Analysis: Calculated for G^2^26^’^' G, 50.00; H, 9.03. Found: G, 50.22; H, 9.13. Allyltricyclohexyltin was synthesized from allyl chlo ride and tricyclohexyltin chloride by Method I in 41% yield, m.p. 26-28°. Analysis: Calculated for C, 61.76; H, 9.31. Found: G, 61.49; H, 9.20. Allyltriphenyltin was obtained from Metal and Thermit Chemicals Inc., Lot 931-6A and was recrystallized from metha nol before use, m.p. 73-74.5°. Analysis (reported by M & T): Calculated for *^21^20^"^' 30.35; Cl, 0.00. Found: Sn, 30.48; Cl, 0.00. P-Methallyltrimethyltin was synthesized from p-methyl- allyl chloride and trimethyltin chloride by Method I in 81% yield, b. p. 147-148°. Analysis: Calculated for C^H^^Sn: C, 38.41; H, 7.37. Found: C, 38.62; H, 7.34. y-Methallyltrimethyltin was synthesized from 3-chloro-l- butene and trimethyltin chloride by Method I in 81% yield, b.p. trans isomer 151.0°, cis isomer 152.5°. The two isomers were separated by gas-liquid chromatography using a 20 ft. column of General Electric XF 1150 silicone nitrile (17%) on Chromosorb P (40-60 mesh) run isothermally at 125°. Analysis: Calculated for CyH^^Sn: C, 38.41; H, 7.37. Found: C, 38.23; H, 7.50. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 133 7 -Methallyltriphenyltin was synthesized from crotyl chloride and triphenyltin chloride by Method II by D. 0. 18 Whittemore in these laboratories, m.p. 51-52°. No sepa ration of the cis and trans isomers was achieved. Analysis: Calculated for ^22^22^'^' H, 5.48. Found: C, 64.72; H, 5.30. y-Methallyltriethyltin was prepared from 3-chloro-l-butene and triethyltin chloride by Method 1 in 70% yield, b.p. mixture of cis and trans isomers 99-105°/20 mm. The two isomers were separated by gas-liquid chromatography using a 20 ft. column of General Electric XF 1150 silicone nitrile (17%) on Chromo sorb P (40-60 mesh) run isothermally at 125°. Analysis: Calculated for ^10^2 2 5 ^: C , 46.15; H, 8.45. Found: C, 45.91; H, 8.60. Cyclopent-2-enyltrimethyltin was synthesized by R. H. Fish in these laboratories by the addition of trimethyltin hydride to cyclopentadiene at 175°. Analysis: Calculated for CgH^gSn: C, 41.61; H, 6.94. Found: C, 41.85; H, 7.14. Cyclohex-2-enyltrimethyltin was synthesized from 3-bromo- cyclohexene (prepared from cyclohexene and N-bromosuccinimide according to the procedure of Schmid and Karrer^^) and tri methyltin chloride by Method II in 22% yield, b.p. 97-101°/ 15 mm. Annalysis: Calculated for CgH^gSn: C, 44.26; H, 7.37. Found: C, 44.60; H, 7.46. Cyclohept-2-enyltrimethyltin was synthesized from 3- bromocycloheptene (prepared from cycloheptene and N-bromo succinimide according to the procedure of Schmid and Karrer ) and trimethyltin chloride by Method II in 26% yield, p.b. 74- 75°/2 mm. Analysis: Calculated for C^gH2 gSn: C, 46.51; H, 7.75. Found: C, 46.59; H, 7.80. Cyclooct-2-enyltrimethyltin was synthesized from 3- bromocyclooctene (prepared from cyclooctene and N-bromo- succinimide according to the procedure of Schmid and Karrer^^) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 134 and trimethyltin chloride by Method II in 40% yield, b.p. 68-70°/0.5 mm. Analysis: Calculated for C^^H2 2 Sn: C, 48.53; H, 8.09. Found: C, 49.34; H, 8.40. 2. Hydrochloric Acid. The hydrochloric acid solu tions used in this study were prepared from standard solu tions of Fisher Reagent grade hydrochloric acid diluted to the appropriate volume with methanol. 3. Salts. All of the metal ion salts used in this work were Matheson, Coleman & Bell A.C.S. Reagent grade nitrates. The specific salts used as addends were copper(II) nitrate, cadmium nitrate, silver nitrate, lead(II) nitrate and zinc(II) nitrate. 4. Solvents. Methanol used in this study was Fisher Certified Reagent grade, containing 0.01-0.05% water, depend ing on the lot, and was used without further purification. The kinetic solvent was prepared by placing 4.00 ml. of re distilled water in a 100 ml. volumetric flask and diluting to the mark with methanol. 5. Trimethyltin Chloride. The trimethyltin chlo ride used in the preparation of the allyltins was crude material from M & T Chemicals Inc. and was used without further purification. 6 . Deuterium Oxide. The deuterium oxide used in the preparation of methanol-d and deuterium chloride was ob tained from the Bio-Rad Laboratories and contained 99.8% D2O. 7. Methanol-d. The methanol-d used in this study was prepared following the procedure of Streitweiser and co- 38 workers. Dimethylcarbonate 400 g. (4.44 moles) and D2O 100 g. (5.0 moles) were placed in a carefully dried 1000 ml. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 135 one-necked flask. DimethyIsulfate 16 g. (0.13 mole) was added and the flask attached to two reflux condensers arranged in series. The flask contents were heated to reflux with provision for moisture exclusion. After re- fluxing for three days the reaction was complete as evi denced by the fact that the carbonyl band in the infra-red had disappeared. The product was distilled through a Vigreux column and then redistilled from a small amount of sodium. A final distillation on a Todd column using glass beads as column packing afforded product in 8 8 % yield. The product was 1 0 0 % pure as determined by gas-liquid chroma tography using a 6 ft. Carbowax 20M column run isothermally at 6 6 °. The amount of deuterium substitution was determined by correlating the relative areas of the bonded OH absorption frequencies at 3300 cm. ^ for a solution of methanol in car bon tetrachloride with the concentration within an experimen tal error of + 3%. The concentration of methanol in methanol-d was determined by preparing a solution of 1 . 00 ml. methanol-d in 25.00 ml. carbon tetrachloride and obtaining the infra-red spectrum using a 0.200 mm. cell. The results are seen in Table XIII. TABLE XIII Percentage Methanol in Methanol-d Runs Relative Area % OH pure methanol^ 54.39 100 T-166-T-173 1.98 3.6 T-174-T-181 1.44 2.6 ^ for calibration Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 136 8 , Deuterium Chloride. Deuterium chloride was con- 37 veniently prepared by the method of Brown and Groot. Deuterium oxide (0.5 mole) was added dropwise to 1.5 mole of benzoyl chloride which had been purified by distillation. After addition was complete the mixture was heated to reflux until DCl was no longer generated. The DCl produced was trapped by passing the gas through methanol-d contained in a 25 ml. volumetric flask. When the reaction was complete the volumetric flask was diluted to the mark with methanol-d and the molarity of the solution determined by titration with standard sodium hydroxide to a phenolphthalein end point. II. GLASSWARE CLEANING PROCEDURE All glassware was cleaned with concentrated nitric acid and rinsed ten times with distilled water and three times with metlanol. The glassware was then dried in an oven at 1 1 0 °. III. PRODUCTS OF CLEAVAGE The products of cleavage of cis-and trans-y-methallyl- trimethyltin with HCl and DCl were identified using the follow ing procedure. An appropriate amount of either the isomer mixture or one of the pure isomers which had been separated by CLC was placed in a 50 ml. three-necked round bottom flask equipped with a pressure equalizing addition funnel and a gas inlet and outlet tube. The inlet tube was connected to a nitrogen tank and prepurified N^ was passed through the system during the subsequent reaction. The outlet tube was connected to a calcium chloride drying tube, a trap immersed in liquid nitrogen and a mercury seal arranged in series. An appropri ate amount of either HCl in methanol or DCl in methanol-d was added dropwise through the addition funnel and the reaction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 137 mixture stirred magnetically. After the reaction was com plete the displaced butenes which had been carried along by the Ng stream and frozen in the trap were withdrawn in a gas syringe and analyzed by gas-liquid chromatography using a 15 ft. column of 28% dimethyIsulfolane on C-22 Firebrick (40-60 mesh). The butenes were identified by comparison of their retention times with the retention times of authentic samples. Product composition was determined using the method 27 of Keulemans. IV. KINETIC PROCEDURE Two kinetic procedures were utilized during the course of this work. Method I - Aliquot method: utilized in runs at 0°. Into a 100 ml. volumetric flask containing 5 ml. of methanol and 10 ml. of allyltin stock solution was pipetted 25 ml. of 8% water-methanol solution. The flask was then immersed in a constant temperature bath maintained at 0 + 0.02°. To start the reaction 10 ml. of a stock solution of HCl in methanol which had been brought to temperature was pipetted into the flask and the stop watch started. At appropriate time intervals 5 ml. aliquots were withdrawn and the reaction quenched by adding to 5 ml. of 0.1 M sodium methoxide in methanol and diluting to 25 ml. with methanol. The absorbance was then measured on a Beckman DU Spectropho tometer. The following equations were used to calculate rate constants : Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 First Order Conditions plot of log(a - x) versus time where x (5/^ ) (A^ - A^) = 2,303 X slope 4 " ki/(HCl)o Second Order Conditions plot of log(a - x)/(b - x) versus time where x (5/g ) (A„ - A p kg = 2.303 X slope/(a - b) Method II - Direct method; utilized in runs at 25°, 35° and 45°. In a specially constructed reaction flask was placed 5 ml. of a stock solution of HCl in methanol (or DCl in methanol-d) and 10 ml. of 8 % water-methanol solution. Five ml. of allyltin stock solution was then pipetted into a con centric cylinder within the flask and the flask stoppered. The reaction flask was brought to temperature in a constant temperature bath and the reaction started by inverting the flask. At this point the stop watch was started. An aliquot was quickly transferred to a cuvette and the absorbance read against an appropriate standard reference as the reaction progressed. The DU Spectrophotometer cell compartment was thermostated and the temperature controlled to + 0.1°. The following equations were used to calculate rate constants: Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 First Order Conditions plot log(A^ - A^) versus time = 2.303 slope kg = ky(HCl)^ Second Order Conditions plot 1/ (A^ - A,^) versus time k2 = 2.303 slope (éL ) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 139 BIBLIOGRAPHY 1. E. G. Rochow, D. T. Hurd and R. N. Lewis, The Chemistry of Organometallic Compounds, John Wiley and Sons, New York, 1957, pp. 142-185. 2. C. E. Coates, Organo-Metallie Compounds, John Wiley and Sons, London, 1960, pp. 206-208. 3. C. Eaborn and J. C. Waters, J. Chem. Soc., 542 (1961); C. Eaborn and K. Pande, ibid., 297 (1961); C. Eaborn and C. E. Webster, ibid., 4449 (1957); 179 (I960); C. Eaborn and K. Pande, ibid., 1556 (I960); C. Eaborn and F. B. Deans, ibid., 2299 (1958). 4. Y . Tsuno, T. Ibata and Y . Yukawa, Bull. Chem. Soc., Japan, 960 (1959) . 5. Y . Yukawa and Y . Tsuno, ibid., 32, 965 (1959). 6 . Y . Yukawa and Y . Tsuno, ibid. , 32, 971 (1959). 7. M. Kanazashi, ibid., 28, 4450 (1955). 8 . L. H. Sommer, C. M. Goldberg, C. E. Buck, T. S. Bye, F . J . Evans and F . W. Whitmore, J. Am. Chem. Soc., 76, 1613 (1954). 9. 0, A. Reutov, Rec. Chem. Progress, 1 (1961). 10. R. E. Dessy and J. Kim, J. Am. Chem. Soc., 83, 1167 (1961). 11. R. E. Dessy, C. F . Reynolds and J. Kim, ibid., 81, 2683 (1959). 12. L. H. Sommer, L. J. Tyler and F . C . Whitmore, ibid., 70, 2872 (1948). 13. D. Crafstein, ibid., 77, 6650 (1955). 14. A. D. Petrov and V. F. Mironov, Angew. Chemie, 73, 59 (1961). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 140 15. S. D. Rosenberg, E. Debreczeni and E. L. Weinberg, J. Am. Chem. Soc., 972 (1959). 16. P. Austin, ibid. , 3514 (1931). 17. H. Cilman, E. B. Towne and H. L. Jones, ibid., 5^^ 4689 (1933). 18. Synthesized by D. 0. Whittemore in these laboratories. 19. M. Cielen and J. Nasielski, Bull. Soc. Chim. Belg., 71, 32 (1962). 20. P. D. Sleezer, S. Winstein and W. C. Young, J. Am. Chem. Soc., 8^, 1890 (1963). 21. M. M. Kreevoy, P J . Steinwand and W. V. Kayser, ibid., 8 6 , 5013 (1964). 22. H. C. Kuivila and J. A. Verdone, Tetr. Let., 2, 119 (1964). 23. J. A. Verdone, Ph.D. Thesis, November, 1963, University of New Hampshire, Durham, N. H. 24. W. J. Jones, W. C. Davies, S. T. Bowden, C. Edwards, V. E. Davies and L. H. Thomas, J. Chem. Soc., 1446 (1947) 25. C. A. Kraus and W. N. Creer, J. Am. Chem. Soc., 4À^ 2629 (1922). 26. R. H. Fish, Ph.D. Thesis, January 1965, University of New Hampshire, Durham, N. H. 27. A. 1. M. Keulemans, Cas Chromatography, Rheinhold Pub lishing Co., London, 1959, pp. 33-34. 28. A. A. Frost and R. C. Pearson, Kinetics and Mechanism, John Wiley and Sons, New York, 1958, p. 17. 29. J. E. Leffler, J. Org. Chem., 20^, 1202 (1955). 30. R. C. Petersen, ibid., 29, 3133 (1964). 31. E. A. Halevi in Progress in Physical Organic Chemistry, edited by S. C. Cohen, A. Streitwieser and R. W. Taft, Interscience Publishers, New York, 1963, p. 191 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 141 32. E. L. Purlee, R. W. Taft and C. A. DeFayio, J. Am. Chem. Soc. , 22, 837 (1955). 33. P. J. C. Fierens and P. Verschelden, Bull. Soc. Chim. Belges., 61, 427,609 (1952). 34. E. L. Eliel, Stereochemistry of Carbon Compounds, MeCraw- Hill Book Co., New York, 1962, p. 267. 35. K. Yasuda and R. Okawara, J. Organometal. Chem., 3, 76 (1965). 36. C. L. M. van der Kirk and M. Lesbre, Rec. Trav. Chim., 74, 1056 (1955). 37. H. C. Brown and C. Croot, J. Am. Chem. Soc., 64,2223 (1942). 38. A. Streitwieser, L. Verbit and P. Stang, J. Org. Chem., 29, 3706 (1964). 39. K. Wieberg, Chem. Rev., 52, 713 (1955). 40. L. Melander, Isotope Effects on Reaction Rates, The Ronald Press Co., New York, 1960, pp. 7-45. 41. F. A. Long and J. Begeleisen, Trans. Far. Soc., 55, 2077 (1959). 42. E. L. Purlee, J. Am. Chem. Soc., 82; 263 (1959); F. A. Long and D. Watson, J. Chem. Soc., 2019 (1958); H. C. Kuivila and K. V. Nahabedian, Chem. and Ind., 1120 (1959). 43. Schmid and Karrer, Helv. Chim. Acta, 22, 573 (1946). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 142 TABLES OF DATA Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 16 -3 m-Chlorobenzeneboronic acid (1.0 x 10 M) Temperature - 90.0°C. Buffer - malonate A = 0.063 u = 0.14 pH =6.70 A = 228.0 mu time (min.) ^t ^t ~ log(A^, - AJ^ 60 0.395 0.332 -0,479 360 0.389 0.326 -0.487 1440 0.358 0.295 -0.530 1750 0.366 0.303 -0.511 10080 0.300 0.237 -0.625 13200 " 0.296 0.233 -0.633 18600 0.162 0.099 -1.004 -6 _i k , - 0.217 X 10 sec. obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 17 _3 m-Methoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate A ^ = 0.015 u = 0.14 pH =6.70 ^ - 290.0 mu time (min.) ^t ^t ' ^ log(A^ - A ^ 120 0.702 0.687 -0.163 240 0.698 0.683 -0.166 600 0.702 0.687 -0.163 4380 0.657 0.642 -0.192 7620 0.604 0.589 -0.230 13020 0.540 0.525 -0.280 17860 0.491 0.476 -0.322 24600 0.410 0.395 -0.403 31080 0.356 0.341 -0.467 k , = 0.343 X 10 '^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 18 _3 m-Fluorobenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Aev== 0.040 u = 0.14 pH = 6.70 X = 225.0 mu log(A^ - time (min.) 30 1.350 1.310 0.117 2880 1.250 1 . 2 1 0 0.083 6060 1.245 1.205 0.081 12780 1.063 1.023 0.009 16290 1 . 0 0 0 0.960 -0.018 23020 0.930 0.890 -0.051 k 0.322 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 19 _2 m-Methylbenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate A ^ = 0.058 u = 0.14 pH = 6.70 X = 230.0 mu time (min.) ^t ^t ~ log (A^. - A ^ 960 1.350 1.292 0.110 2820 1.250 1.192 0.076 5880 1.318 1.260 0.100 12600 1.157 1.099 0.04H 16110 1.091 1.033 0.014 22840 0.938 0.880 -0.056 k , = 0.294 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 20 _2 2,6 -Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 1.0 X 10 M perchloric acid 0.030 u = 0.50 pH = 3.00 X = 290.0 mu - time (miu.) At A(- - log(A^ 5 0.641 0.611 -0.214 10 0.639 0.609 -0.215 20 0.635 0.605 -0.218 30 0.620 0.590 -0.229 40 0.609 0.579 -0.237 50 0.605 0.575 -0.240 60 0.598 0.568 -0.246 70 0.592 0.562 -0.250 k , = 21.3 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 21 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 4.0 X 10 M perchloric acid A ^ - 0.030 u - 0.50 pH =2.40 X = 290.0 mu time (min.) - A^ log(A^ -Aj^ 5 0.546 0.516 -0.287 20 0.496 0.466 -0.332 40 0.442 0.412 -0.385 60 0.396 0.366 -0.437 70 0.390 0.360 -0.444 80 0.362 0.332 -0.479 95 0.340 0.310 -0.509 110 0.318 0.288 -0.541 k , 94.0 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 22 “3 2,6-Dimethoxybenzeneboronic acid (9.0 x 10 M) Temperature - 90.0°C. _3 1.0 X 10 M perchloric acid 0.030 u = 0.50 pH = 3.00 = 290.0 mu log(A^ - time (min.) h A).. 5 1.000 0.970 -0.013 20 0.980 0.950 -0.022 40 0.958 0.926 -0.032 60 0.935 0.905 -0.043 60 0.900 0.870 -0.060 100 0.882 0.852 -0.070 122 0.840 0.810 -0.092 140 0.830 0.800 -0.097 k , = 20.2 X 10“^sec."^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 23 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -2 1.0 X 10 M perchloric acid A =0.030 u = 0.50 pH = 2.00 X = 290.0 mu A, - A log(A^ -A ^ time (min.) Ap c CAO 10 0.466 0.436 -0.361 20 0.414 0.384 -0.416 25 0.383 0.353 -0.452 30 0.350 0.320 -0.492 35 0.329 0.299 -0.524 40 0.311 0.281 -0.551 45 0.287 0.257 -0.590 50 0.280 0.250 -0.602 , „-6 -1 k ^ = 230 X 10 sec. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 24 “3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _3 4.0 X 10 M perchloric acid 0.030 u = 0.14 pH = 2.40 X = 290.0 mu time (min.) \ ~ log(A^_ -A)^ 5 0.549 0.519 -0.285 25 0.488 0.458 -0.340 45 0.447 0.417 -0.380 65 0.400 0.370 -0.432 85 0.367 0.337 -0.472 105 0.332 0.302 -0.520 125 0.305 0.275 -0.561 140 0.289 0.259 -0.587 k , = 87.4 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 26 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _3 2.0 X 10 M perchloric acid 0.030 u = 0.14 pH =2.70 X = 290.0 mu log(A^ - time (min.) 5 0.588 0.558 -0.253 20 0.555 0.525 -0.280 40 0.533 0.503 -0.298 60 0.512 0.482 -0.317 80 0.492 0.462 -0.335 100 0.469 0.439 -0.358 120 0.445 0.415 -0.382 140 0.395 0.365 -0.438 k , = 34.5 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 31 m-Fluorobenzeneboronic acid (5.0 x 10 ^M) Temperature - 90.0°C. Buffer - malonate 0.005 u = 0.14 pH = 6.70 X = 225.0 mu log(A^ - time (min.) At At - A*. 1440 0.307 0.302 -0.520 2760 0.234 0.229 -0.640 4200 0.221 0.216 -0.666 9450 0.195 0.190 -0.721 17280 0.173 0.168 -0.775 k , = 0.692 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 32 _3 m-Chlorobenzeneboronic acid (5.0 x 10 M) Temperature - 90.0°C. Buffer - malonate 0.275 u = 0.14 pH =6.70 X = 228.0 mu time (min.) log(A^ - A ^ 1440 1.592 1.317 0.120 2760 1.556 1.281 0.107 4200 1.511 1.236 0.093 9450 1.318 1.043 0.018 17280 1.038 0.763 -0.117 k = 0.377 X lO'^sec."^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 33 _2 m-Methylbenzeneboronic acid (1.0 x 10 M) Temperature - 90.0°G. Buffer - malonate 0.013 u = 0.14 pH =- 6.70 X = 230.0 mu time (min.) ^t ^ t _ ] _ ^ log(A^ - A^, 1440 0.318 0.305 -0.516 2760 0.307 0.294 -0.532 4200 0.297 0.284 -0.547 9450 0.278 0.265 -0.577 17280 0.261 0.248 -0.606 k , " 0.465 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 34 -3 m-Methoxybenzeneboronic acid (5,0 x 10 M) Temperature - 90.0°C. Buffer - malonate A _= 0.015 u - 0.14 pH - 6.70 = 290.0 mu time (min.) 1440 0.828 0.813 -0.093 2760 0.840 0.825 -0.086 4200 0.822 0.807 -0.096 9450 0.780 0.765 -0.119 17280 0.681 0.666 -0.180 18750 0.467 0.452 -0.350 k , 0.237 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 45 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 1.0 X 10 M perchloric acid Added Salt - 1.0 x 10 '^M cadmium nitrate A 0.030 u - 0.14 pH = 3.10 h 290.0 mu log(A^ - ^ time (min.) At - A^ 5 0.616 0.586 -0.232 15 0.605 0.575 -0.240 30 0.598 0.568 -0.246 90 0.561 0.531 -0.275 150 0.512 0.482 -0.317 195 0.504 0.474 -0.324 255 0.468 0.438 -0.359 270 0.452 0.422 -0.375 k , ^ 19.5 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 46 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _2 1.0 X 10 M perchloric acid -4 Added Salt - 1.0 x 10 M cadmium nitrate A,^= 0.030 u - 0.14 pH =2.20 X = 290.0 mu t ime (min. ) h Ap - A ^ log(A^ - ^ 5 0.610 0.580 -0.237 15 0.570 0.540 -0.268 25 0.500 0.470 -0.328 35 0.446 0.416 -0.381 45 0.410 0.380 -0.420 55 0.367 0.337 -0.472 65 0.332 0.302 -0.520 70 0.326 0.296 -0.529 176 X 101 - sec. 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 47 “3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90,0°C. -3 4.0 X 10 M perchloric acid -4 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.030 u = 0.14 pH =2.47 K = 290.0 mu A^ - A ^ log(A^ - time (min.) 5 0.662 0.632 -0.199 20 0.619 0.589 -0.230 60 0.513 0.483 -0.316 80 0.478 0.448 -0.349 100 0.435 0.405 -0.393 120 0.382 0.352 -0.453 140 0.353 0.323 -0.491 160 0.327 0.297 -0.528 k , = 82.4 X 10 °sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 48 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 2.0 X 10 M perchloric acid Added Salt - 1.0 x 10 cadmium nitrate A^^= 0.030 u = 0.14 pH = 2.91 X = 290.0 mu log(A^ - time fmin.) \ 10 0.682 0.652 -0.186 30 0.655 0.625 -0.204 60 0.610 0.580 -0.237 80 0.583 0.553 -0.257 100 0.560 0.530 -0.276 120 0.520 0.490 -0.310 140 0.499 0.469 -0.329 160 0.462 0.432 -0.365 k , = 42.1 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 49 “3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _2 1.0 X 10 M perchloric acid _3 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.030 u = 0.14 pH =2.24 X = 290.0 mu time (min.) ^t ^t ~ log(A^_ - A ^ 10 0.588 0.558 -0.253 20 0.530 0.500 -0.301 30 0.488 0.458 -0.339 40 0.428 0.398 -0.400 50 0.371 0.341 -0.467 60 0.346 0.316 -0.572 k , = 190 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 51 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -4 5.0 X 10 M perchloric iacid.... -4 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.030 u = 0.14 pH = 3.18 .X = 290.0 mu A log(A^ - time (min.) t \ 10 0.622 0.592 -0.228 60 0.600 0.570 -0.244 120 0.582 0.552 -0.258 240 0.513 0.483 -0.316 300 0.500 0.470 -0.328 375 0.465 0.435 -0.362 420 0.470 0.440 -0.357 k , = 15.4 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 52 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -4 2.0 X 10 M perchloric acid -4 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.030 u = 0.14 pH =3.62 h = 290.0 mu log (A^ - a ; time (min.) At - A_ 15 0.621 0.591 -0.228 60 0.596 0.566 -0.247 120 0.586 0.556 -0.255 240 0.531 0.501 -0.300 300 0.499 0.469 -0.328 375 0.470 0.440 -0.357 420 0.420 0.390 -0.409 k , = 13.4 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 53 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 1.0 X 10 M perchloric acid -3 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.030 u = 0.14 pH = 3.18 A = 290.0 mu log(A|_ - time (min.) Aj- - A ^ 10 0.620 0.590 -0.230 60 0.558 0.528 -0.277 120 0.480 0.450 -0.337 661 0.196 0.166 -0.780 720 0.176 0.146 -0.836 780 0.166 0.136 -0.867 840 0.147 0.117 -0.932 k , = 32.2 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 54 2,6-Dimethoxybenzeneboronic acid Temperature - 90.0°C. “3 1.0 X 10 M perchloric acid _ 2 Added Salt - 1.0 x 10 M cadmium nitrate 0.030 u = 0.14 pH =3.32 X = 290.0 mu log(A^ - A L time (min.) ^t - 15 0.585 0.555 -0.256 30 0.533 0.503 -0.298 45 0.482 0.452 -0.345 60 0.452 0.422 -0.375 75 0.420 0.390 -0.409 90 0.382 0.352 -0.453 105 0.357 0.327 -0.485 k , = 98.4 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 60 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 1.0 X 10 M perchloric acid -2 Added Salt - 5.0 x 10 M cadmium nitrate A^,- 0.030 u = 0.14 pH = 3.42 \ = 290.0 mu log(A^ - A ^ t ime (min. ) 5 0.661 0.631 -0.200 25 0.439 0.409 -0.388 40 0.337 0.307 -0.513 45 0.294 0.264 -0.578 55 0.261 0.231 -0.636 70 0.214 0.184 -0.735 85 0.187 0.157 -0.804 k . - 312 X 101 o sec. -1 obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 61 _3 2,6-Dimethoxybenzeneboronic acid (4,45 x 10 M) Temperature - 90.0°C. -3 1.0 X 10 M perchloric acid _3 Added Salt - 5.0 x 10 M cadmium nitrate A_. = 0.030 u = 0.14 pH = 3.47 X = 290.0 mu log(A^ - A ^ time (min.) 5 0.605 0.575 -0.240 25 0.572 0.542 -0.266 40 0.542 0.512 -0.291 55 0.515 0.485 -0.314 70 0.491 0.461 -0.336 85 0.472 0.442 -0.354 100 0.447 0.417 -0.380 1 - 1 k ^ = 66.2 X 10 sec. obs Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 62 m-Fluorobenzeneboronic acid (7.0 x 10 ^M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.007 u = 0.14 pH = 6.70 K = 225.0 mu A - A time (min.) log (A^ - ^ 10 0.531 0.524 -0.281 60 0.502 0.495 -0.305 120 0.478 0.471 -0.327 180 0.468 0.461 -0.336 240 0.417 0.410 -0.387 300 0.432 0.425 -0.372 360 0.418 0.411 -0.386 480 0.390 0.383 -0.417 k , = 11.3 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 63 -4 m-Chlorobenzeneboronic acid (7.0 x 10 M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt - 1.0 x 10 M cadmium nitrate A^^= 0.042 u = 0.14 pH = 6.70 K = 228.0 mu time (min.) ^t \ log(A^ - 10 0.444 0.402 -0.396 60 0.393 0.351 -0.455 120 0.317 0.275 -0.561 180 0.311 0.269 -0.570 240 0.288 0.246 -0.613 300 0.251 0.209 -0.680 k , = 35.2 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 64 -3 m-Methylbenzeneboronic acid (5.0 x 10 M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.070 u = 0.14 pH = 6.70 X = 230.0 mu log(A^ - A ^ time (min.) \ 10 1.600 1.530 0.200 62 0.983 0.913 -0.040 180 0.856 0.786 -0.105 240 0.825 0.755 -0.128 270 0.761 0.691 -0.161 300 0.743 0.673 -0.182 330 0.721 0.651 -0.186 k , = 20.8 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 65 -3 m-Methoxybenzeneboronic acid (5.0 xlO M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt- 1.0 x 10 M cadmium nitrate A ^ = 0.020 u = 0.14 pH = 6.70 X = 290.0 mu time (min.) ^t 1°§ (A^ 10 1.028 1.008 0.003 60 0.535 0.515 -0.288 180 0.430 0.410 -0.387 240 0.382 0.362 -0.441 270 0.368 0.348 -0.458 300 0.345 0.325 -0.488 330 0.329 0.309 -0.510 k , = 32.2 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 66 “3 m-Methylbenzeneboronic acid (5.0 x 10 M) Temperature - 90.0°C. Buffer - malonate -4 Added Salt - 5.0 x 10 M cadmium nitrate A ^ = 0.070 u = 0.14 pH =6.70 X = 230.0 mu time (min.) ^t ^t ~ log(A^ - A ^ 15 1.471 1.401 0.146 60 r.437 1.367 0.136 240 1.293 1.223 0.087 360 1.214 1.144 0.047 1140 0.780 0.710 -0.149 1200 0.762 0.692 -0.160 k , = 10.1 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 67 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _3 Buffer - malonate 1.80 x 10 M 0.030 u = 0.14 pH = 3.54 X = 290.0 mu time (min.) log(A^ - A^ 10 0.678 0.648 -0.188 60 0.650 0.620 -0.208 120 0.623 0.593 -0.227 245 0.588 0.558 -0.253 420 0.542 0.512 -0.291 k , = 9.64 X 10 sec. obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 68 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _3 Buffer - malonate 3.56 x 10 M 0.030 u = 0.14 pH =3.56 X = 290.0 mu time (min.) ^t ^t ~ log(A^. - A^ 15 0.684 0.654 -0.184 65 0.655 0.625 -0.204 125 0.616 0.586 -0.232 245 0.566 0.536 -0.271 425 0.492 0.462 -0.335 k , -14.0 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 69 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate 3.16 x 10 M A ^ = 0.030 u = 0.14 pH = 3.72 X = 290.0 mu time (min.) At A^ - A^ log(A^ - A^ 20 0.651 0.621 -0.207 70 0.625 0.595 -0.225 130 0.612 0.582 -0.235 250 0.590 0.560 -0.252 430 0.548 0.518 -0.286 k , = 7.25 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 70 "3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _3 Buffer - malonate 1.38 x 10 M A^,= 0.030 u = 0.14 pH = 3.59 _ , X = 290.0 mu A^ - A ^ log(A^ - A ^ time (min.) 10 0.655 0.625 -0.204 60 0.637 0.607 -0.217 120 0.624 0.594 -0.226 360 0.550 0.520 -0.284 420 0.536 0.506 -0.296 540 0.492 0.462 -0.335 600 0.482 0.452 -0.345 k , = 8.92 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 71 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _3 Buffer - malonate 2.74 x 10 M 0.030 u = 0.14 pH = 3.59 X 290.0 mu time (min.) Aj- - A ^ log (At - A ^ 10 0.638 0.608 -0.216 60 0.610 0.580 -0.237 120 0.583 0.553 -0.257 360 0.495 0.465 -0.333 420 0.478 0.448 -0.349 540 0.431 0.401 -0.397 600 0.421 0.391 -0.408 - k Kc 12.5 X 10 ^sec. ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 72 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _3 Buffer - malonate 6.00 x 10 M 0.030 u = 0.14 pH = 3.39 X =290.0 mu time (min.) “ Acxs log(A^ - A^ 15 0.651 0.621 -0.207 60 0.617 0.587 -0.231 120 0.583 0.553 -0.257 360 0.459 0.429 -0.368 420 0.430 0.400 -0.398 540 0.368 0.338 -0.471 k , - 18.1 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 73 “ 3 2,6-Dimethoxybenzeneboronic acid (4,45 x 10 M) Temperature - 90.0°C. -3 Buffer - malonate 1.17 x 10 M 0.030 u = 0.14 pH =- 3.67 \ = 290.0 mu time (min.) - A ^ log(A^ - 15 0.588 0.558 -0.253 60 0.570 0.540 -0.268 630 0.432 0.402. -0.396 690 0.419 0.389 -0.410 750 0.408 0.378 -0.423 930 0.367 0.337 -0.472 1230 0.355 0.325 -0.488 ,»-6 -1 k , - 8.60 X 10 sec. obx. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 74 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0“C. _3 Buffer - malonate 0.58 x 10 M 0.030 u - 0.14 pH ^ 3.67 X ^ 290.0 mu time (min.) ^t ^t ~ log (A^ - A)^ 15 0.597 0.567 -0.246 60 0.582 0.552 -0.258 630 0.478 0.448 -0.349 690 0.461 0.431 -0.366 750 0.454 0.424 -0.373 930 0.431 0.401 -0.397 1230 0.423 0.393 -0.406 k , 6.12 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 75 _2 2,6-Dimethoxybenzeneboronic acid (4,45 x 10 M) Temperature - 90.0°C. -3 Buffer - malonate 0.27 x 10 M A ^ = 0.030 u = 0.14 pH = 3.70 \ - 290.0 mu log(A^ - A^ t ime (min. ) At At - A., 15 0.590 0.560 -0.252 60 0.584 0.554 -0.256 630 0.488 0.458 -0.339 690 0.477 0.447 -0.350 750 0.474 0.444 -0.353 930 0.448 0.418 -0.379 1230 0.428 0.398 -0.400 k , ^ 5.11 X 101 sec. -1 obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 76 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. _Q Buffer - malonate 11.7 x 10 M A ^ = 0.030 - 0.14 pH = 3.61 A ^ 290.0 mu time (min.) ~ 4% log(A^ ~ ^ 10 0.630 0.600 -0.222 60 0.582 0.552 -0.258 270 0.443 0.413 -0.384 360 0.402 0.372 -0.429 600 0.323 0.293 -0.533 660 0.280 0.250 -0.602 k , = 21.9 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 77 _2 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate 6.00 x 10 M A«,= 0.030 u -- 0.14 pH ^ 3.55 \ 290.0 mu time (min.) At Aj. - A_ log(A^ - AZ 10 0.622 0.592 -0.228 60 0.595 0.565 -0.248 270 0.507 0.477 -0.321 360 0.478 0.448 -0.349 600 0.430 0.400 -0.398 660 0.424 0.394 -0.404 , -6 -1 k ^ - 12.9 X 10 sec. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 78 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 -3 M Temperature - 90.0°C. Buffer - malonate 0.030 u - 0.14 pH - 3.53 A - 290.0 mu log(A - A) time (min.) At - A_ C CC' 10 0.619 0.589 -0.230 60 0.608 0.578 -0.238 810 0.390 0.360 -0.444 930 0.386 0.356 -0.449 1020 0.366 0.336 -0.474 1200 0.353 0.323 -0.491 1410 0.320 0.290 -0.538 1 " 1 k 1 - 5.96 X 10 sec. obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 79 m-Chlorobenzeneboronic acid (7.0 x 10 ^M) Temperature - 90.0°C. Buffer - malonate -4 Added Salt - 5.0 x 10 M cadmium nitrate A ^ = 0.042 u - 0.14 pH = 6.70 "X -- 228.0 mu log(A - A) time (min.) A L 10 0.364 0.322 -0.492 60 0.304 0.262 -0.582 75 0.301 0.259 -0.587 120 0.287 0.245 -0.614 280 0.250 0.208 -0.682 360 0.238 0.196 -0.708 410 0.214 0.172 -0.764 k , 19.8 X lO^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 80 -4 m-Fluorobenzeneboronic acid (7.0 x 10 M) Temperature - 90.0°C. Buffer - malonate - 4 Added Salt - 5.0 x 10 M cadmium nitrate A ^ = 0.007 u -- 0.14 pH -- 6.70 )\ 225.0 mu log(A^ - A2 time (min.) A At - A _ 10 0.356 0.349 -0.457 60 0.335 0.328 -0.484 120 0.316 0.309 -0.510 180 0.324 0.317 -0.499 240 0.309 0.302 -0.520 370 0.295 0.288 -0.542 420 0.288 0.281 -0.551 k . - 6.49 X 101 - sec. 1 obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 81 _2 m-Methoxybenzeneboronic acid (5.0 x 10 M) Temperature - 90.0°C. Buffer - malonate -4 Added Salt - 5.0 x 10 M cadmium nitrate A ^ - 0.020 u = 0.14 pH = 6.70 X "=290.0 mu time (min.) ~ log (A^ " 10 0.553 0.533 -0.273 60 0.532 0.512 -0.291 120 0.501 0.481 -0.318 180 0.502 0.482 -0.317 310 0.437 0.417 -0.380 360 0.421 0.401 -0:397 420 0.394 0.374 -0.427 k , =- 14.5 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 82 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10,-3, M) Temperature - 90.0°C. Buffer - malonate 0.030 u - 0.14 pH = 3.81 \ - 290.0 mu time (min.) \ log(A^ - A^ 10 0.625 0.595 -0.225 120 0.590 0.560 -0.252 810 0.502 0.472 -0.326 930 0.480 0.450 -0.347 1020 0.491 0.461 -0.336 1200 0.472 0.442 -0.355 k , " 3.66 X 10 "^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 83 -3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate 3.90 x 10 M A - 0.030 u = 0.14 pH =3.76 X = 290.0 mu A^ - A log(Aj. - A)^ t ime (min. ) At t o r , 15 0.611 0.581 -0.236 60 0.598 0.568 -0.246 120 0.574 0.544 -0.264 180 0.561 0.531 -0.275 240 0.543 0.513 -0.290 k , = 9.27 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 84 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 Buffer - malonate 56.0 x 10 M 0.030 pH = 3.55 X = 290.0 mu /L - A log(A^ - time (min.) h t 15 0.611 0.581 -0.236 60 0.532 0.502 -0.299 120 0.460 0.430 -0.367 180 0.395 0.365 -0.438 240 0.343 0.313 -0.504 k , = 46.9 X 101 - sec. 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 85 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 Buffer - malonate 6.00 x 10 M A - 0.030 ^)H = 3.58 X - 290.0 mu A - A log(A^ - Time (min.) At L 15 0.623 0.593 -0.227 60 0.602-» 0.572 -0.243 120 0.568 0.538 -0.270 180 0.555 0.525 -0.280 240 0.530 0.500 -0.301 k , = 11.8 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 86 _2 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°G. - 3 Buffer - malonate 18.0 x 10 M A = 0.030 u = 0.14 pH = 3.65 X = 290.0 mu Time (min.) ~ log(A^ - A^ 10 0.620 0.590 -0.229 60 0.561 0.531 -0.275 120 0.511 0.481 -0.318 180 0.464 0.434 -0.363 240 0.420 0.390 -0.408 k, = 30.3 X 10 ^sec. ^ obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 87 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 Buffer - malonate 50.4 x 10 M A = 0.030 u = 0.26 pH =3.50 X =290.0 mu A - A log(A^ - t ime (min. ) At t f 10 0.624 0.594 -0.226 60 0.522 0.492 -0.308 120 0.425 0.395 -0.403 180 0.355 0.325 -0.488 240 0.283 0.253 -0.597 k . = 55.2 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 88 -3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 Buffer - malonate 47.4 x 10 M = 0.030 u = 0.32 pH = 3.62 X = 290.0 mu time (min.) \ . log(A^ - 7Q 15 0.592 0.562 -0.250 60 0.515 0.485 -0.314 90 0.460 0.430 -0.367 120 0.427 0.397 -0.401 150 0.387 0.357 -0.447 180 0.352 0.322 -0.492 195 0.343 0.313 -0.504 =- 54.6 X 10 ^sec. ^ 'obs Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 89 *3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. -3 Buffer - malonate 74.6 x 10 M A = 0.030 u = 0.46 pH = 3.58 k = 290.0 mu log(A -A) time (min.) At A(. - L f." 15 0.590 0.560 -0.252 60 0.478 0.448 -0.349 90 0.422 0.392 -0.407 120 0.386 0.356 -0.449 150 0.334 0.304 -0.517 180 0.292 0.262 -0.582 195 0.277 0.247 -0.607 , p,-6 -1 k , - 74.9 xlO sec. obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 90 _2 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate 0.030 u = 0.40 pH =6.70 X = 290.0 mu time (min.) At \ - K < , log(A^ - ^ 15 0.598 0.568 -0.246 60 0.498 0.468 -0.330 120 0.399 0.369 -0.433 240 0.265 0.235 -0.629 300 0.214 0.184 -0.735 390 0.166 0.136 -0.866 420 0.143 0.113 -0.947 101 o “ ^ sec. -1 k obs.. = 17.9 X Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 91 “3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate 0.030 u = 0.20 pH = 6.70 X = 290.0 mu - A - A log(A^ - A) t ime (min.) At t 15 0.619 0.589 -0.230 90 0.578 0.548 -0.261 120 0.558 0.528 -0.277 180 0.527 0.497 -0.304 241 0.504 0.474 -0.324 k 18.8 X 10 ^sec. ^ obs Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 92 _ j 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate A = 0.030 u = 0.14 I pH = 6.70 = 290.0 mu A. - A log(A^ time (min.) At t 10 0.628 0.598 -0.223 60 0.582 0.552 -0.258 240 0.444 0.414 -0.383 300 0.405 0.375 -0.426 360 0.380 0.350 -0.456 420 0.328 0.298 -0.526 1080 0.189 0.159 -0.799 . 1140 0.155 0.125 -0.903 1200 0.160 0.130 -0.886 -6 1 19.2 X 10 sec. obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 93 “3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate = 0.030 u = 0.04 pH = 6.70 k = 290.0 mu A — A log(A^ - time (min.) A t 15 0.609 0.579 -0.237 60 0.570 0.540 -0.268 120 0.531 0.501 -0.300 240 0.457 0.427 -0.370 300 0.419 0.389 -0.410 390 0.386 0.356 -0.449 420 0.355 0.325 -0.488 k , = 23.4 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 110 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate -5 Added Satl - 1.0 x 10 M cadmium nitrate A = 0.030 u = 0.14 pH = 6.70 = 290.0 mu log (A - A) t ime (min. ) At At - 4.. L c: 5 0.602 0.572 -0.243 15 0.576 0.546 -0.263 30 0.543 0.513 -0.290 45 0.502 0.472 -0.326 60 0.478 0.448 -0.349 81 0.440 0.410 -0.387 90 0.424 0.394 -0.404 ,„-6 -1 = 76.6 X 10 sec. ^obs 1 -1 - = 5.85 M “ sec. ^Cd. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 111 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Salt - 1.0 x 10 copper(II) nitrate A_ = 0.030 u = 0.14 pH = 6.70 k = 290.0 mu A - A time (min.) At t iog(A^ - 42, 5 0.568 0.538 -0.269 15 0.444 0.414 -0.383 30 0.298 0.268 -0.572 35 0.272 0.242 -0.616 40 0.247 0.217 -0.664 45 0.219 0.189 -0.724 50 0.191 0.161 -0.793 - 404 X 1 10 - sec. 1 ^obs = 38.6 M 1 sec. -1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 112 -3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0“C. Buffer - malonate Added Salt - none, control run A ^ = 0.030 u = 0.14 pH = 6.70 A = 290.0 mu A A - A log (A - A) t ime (min.) 10 0.608 0.578 -0.238 30 0.593 0.563 -0.249 80 0.568 0.538 -0.269 181 0.523 0.493 -0.307 330 0.449 0.419 -0.378 360 0.444 0.414 -0.383 366 0.403 0.373 -0.428 -6 -1 k , = 17.1 X 10 sec. obs . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 114 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Satl- 1.0 x 10 zinc nitrate A = 0.030 u = 0.14 pH = 6.70 X = 290.0 mu log(A^ - time (min.) _ ^ t _ At - Ap. 5 0.602 0.572 -0.243 15 0.590 0.560 -0.252 30 0.575 0.545 -0.264 45 0.556 0.526 -0.279 60 0.546 0.516 -0.287 75 0.533 0.503 -0.298 95 0.503 0.473 -0.325 ,^“6 -1 - 32.2 X 10 sec. ^obs -1 = 1.41 M"~ sec. ^Zn. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 115 _2 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Salt - 1.0 x 10 lead nitrate A ^ = 0.030 u = 0.14 pH = 6.70 h - 290.0 mu time (min.) \ \ ~ log(A^ - A)^ 5 0.591 0.561 -0:251 15 0.505 0.475 -0.323 30 0.419 0.389 -0.410 46.5 0.332 0.302 -0.520 60 0.280 0.250 -0.602 76.5 0.226 _ 0.196 -0.708 90 0.186 0.156 -0.807 k , = 245 X 10 ^sec. ^ obs k„, = 22.7 M ^sec. ^ ^Pb. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 116 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt - 1.0 x 10 M sodium nitrate A^. = 0.030 u u - 0.14 pH = 6.70 j'y 290.0 mu A - A log (A^ - A^^ time (min.) t t'-xo 10 0.612 0.582 -0.235 60 0.582 0.552 -0.258 132 0.551 0.521 -0.283 ' 180 0.515 0.485 -0.314 241 0.484 0.454 -0.343 300 0.470 0.440 -0.357 330 0.450 0.420 -0.377 -6 -1 ^ 17.8 X 10 sec. obs. no catalysis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 117 _2 2,6-Dlmethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt - 1.0 x 10 M potassium nitrate A = 0.030 u - 0.14 pH = 6.70 r\ = 290.0 mu time (min.) ^t ^t ~ log(A^. - A)^ 10 0.592 0.562 -0.250 60 0.575 0.545 -0.264 132 0.538 0.508 -0.294 180 0.510 0.480 -0.319 241 0.481 0.451 -0.346 300 0.477 0.447 -0.350 330 0.462 0.432 -0.365 -6 -1 = 16.1 X 10 sec. ^obs no catalysis ■ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 118 _2 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate _3 Added Salt - 1.0 x 10 M lithium nitrate A^ = 0.030 u = 0.14 pH = 6.70 = 290.0 mu log(A^ - time (min.) ^ 10 0.600 0.570 -0.244 60 0.570 0.540 -0.268 120 0.552 0.522 -0.282 300 0.472 0.442 -0.355 390 0.442 0.412 -0.385 A21 0.420 0.390 -0.409 k , - 15.4 X 10 °sec. ^ obs. no catalysis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 119 _2 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt - 1.0 x 10 M aluminum nitrate A_^= 0.030 u = 0.14 pH = 6.70 = 290.0 mu A - A log(A|. - time (min.) t 10 0.602 0.572 -0.243 60 0.582 0.552 -0.258 120 0.560 0.530 -0.276 300 0.483 0.453 -0.344 390 0.470 0.440 -0.357 421 0.439 0.409 -0.388 -6 -1 c , ^ 14.9 X 10 sec. obs. ^A1 ' catalysis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 120 _2 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate “3 Added Salt - 1.0 x 10 M magnesium nitrate A ^ = 0.030 u = 0.14 pH = 6.70 A = 290.0 mu A - A time (min.) t log(A^ - A^ 10 0.592 0.562 -0.250 60 0.566 0.536 -0.271 120 0.510 0.480 -0.319 300 0.386 0.356 -0.449 390 0.313 0.283 -0.548 421 0.301 0.271 -0.567 ,„-6 -1 = 30.6 X 10 sec. ^obs -1 -1 = 0.0125 M sec. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 121 -3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate _3 Added Salt - 1.0 x 10 M cobalt(II) nitrate A ^ = 0.030 u - 0.14 pH = 6.70 K = 290.0 mu time (min.) ^t ^t ' ^ lgg(A^ - A%^ 15 0.585 0.555 -0.256 45 0.562 0.532 -0.274 ISO 0.390 0.360 -0.444 241 0.302 0.272 -0.565 300 0.282 0.252 -0.599 360 0.217 0.187 -0.728 480 0.194 0.164 -0.785 6 -1 k , - 51.3 X 10" sec. obs - 0.0332 M"^sec.“^ ^Co Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 122 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Salt - 1.0 x 10 nickle(II) nitrate A - 0.030 u - 0.14 (p.-p pH =6.70 ^=290.0 mu A A^ - A time (min.) t t log(A^ - AL, 15 0.579 0.549 -0.260 45 0.580 0.550 -0.260 180 0.462 0.432 -0.365 241 0.445 0.415 -0.382 300 0.383 0.353 -0.452 360 0.380 0.350 -0.456 480 0.320 0.290 -0.538 , « - 6 -1 k , =" 23 .0 X 10 sec. obs. kjyj^ 0.0049 M ^sec Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 123 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate -3 Added Satl - 1.0 x 10 M chromium nitrate A ^ = 0.030 u - 0.14 pH = 6.70 A = 290.0 mu time (min.) ^t ^t ' log(A^. - ^ 10 0.597 0.567 -0.246 60 0.578 0.548 -0.261 120 0.562 0.532 -0.274 180 0.515 0.485 -0.314 360 0.448 0.418 -0.379 480 0.372 0.342 -0.466 660 0.380 0.350 _ -0.456 k , - 17.8 X 10 ^sec. ^ obs. kcr no catalysis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 133 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate -5 Added Satl - 1.0 x 10 M lead nitrate A ^ = 0.030 u = 0.14 pH = 6.70 f\ = 290.0 mu log(A^ - A)^ time (min.) ''t ^ 10 0.555 0.525 -0.280 20 0.481 0.451 -0.346 30 0.422 0.392 -0.407 40 0.403 0.373 -0.428 51 0.343 0.313 -0.504 60 0.283 0.253 -0.597 70 0.250 0.220 -0.658 6 -1 k , - 244 X 10" sec. obs = 22.6 M ^sec. ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 134 _2 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0“C. Buffer - malonate Added Salt - 1.0 x 10 zinc nitrate A = 0.030 u = 0.14 pH = 6.70 K = 290.0 mu \ - A^^ log(A^ - A]^ time (min.) 15 0.582 0.552 -0.258 30 0.546 0.516 -0.287 60 0.514 0.484 -0.315 90 0.502 0.472 -0.326 120 0.457 0.427 -0.370 165 0.428 0.398 -0.400 180 0.406 0.376 -0.425 = 35.2 X 10 ^sec. ^ ^obs k„ - 1.71 M'^sec."^ 'Zn. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 141 _3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate _3 Added Salt - 1.0 x 10 M aluminum nitrate A = 0.030 u = 0.14 pH = 6.70 A = 290.0 mu A - A log(A^ - A)^ t ime (min. ) L_ t 10 0.620 0.590 -0.229 60 0.596 0.566 -0.247 120 0.579 0.549 -0.260 180 0.545 0.515 -0.288 360 0.472 0.442 -0.355 480 0.405 0.375 -0.426 660 0.372 0.342 -0.466 k - 14.3 X 10 ^sec. ^ obs. ^A1 ^ catalysis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 143 _2 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Salt - 1.0 x 10 copper(II) nitrate A ^ = 0.030 u - 0.14 pH =6.70 A " 290.0 mu time (min.) At - A_ log(A^ - A%^ 5 0.583 0.553 -0.257 10 0.515 0.485 -0.314 15 0.442 0.412 -0.385 20 0.403 0.373 -0.428 25 0.354 0.324 -0.489 30 0.325 0.295 -0.530 35 0.280 0.250 -0.602 . ^-6 -1 k , = 437 X 10 sec. = 41.9 M ^sec. ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^ RUN 144 _2 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added satl - 1.0 x 10 cadmium nitrate A ^ = 0.030 u = 0.14 pH = 6.70 A = 290.0 mu time (min.) log(A^ - A) 7.5 0.597 0.567 -0.246 15 0.578 0.548 -0.261 30 0.542 0.512 -0.291 45 0.525 0.495 -0.305 60 0.508 0.478 -0.321 75 0.465, 0.435 -0.362 105 0.417 0.387 -0.411 ■6 -1 k , = 66.7 X 10 sec. obs. -1 4.86 M ^sec. ^Cd " Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 145 _3 p-Chlorobenzeneboronic acid (1.0 x 10 M) Temperature - 90.0°C. Buffer - malonate _3 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.219 u = 0.14 pH = 6.70 A = 227.0 mu A^ - A log(A^ - A) time (min.) t ir>-) 10 1.596 1.377 0.139 60 1.412 ,1.193 0.077 - 90 1.329 1.110 0.045 120 1.252 1.033 0.014 180 1.090 0.871 -0.060 210 0.980 0.761 -0.119 240 0.915 0.696 -0.158 k = 50.3 X 101 " sec. 1 obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 146 _3 p-Methylbenzeneboronic acid (1.0 x 10 M) Temperature - 90.0°C. Buffer - malonate -3 Added Salt - 1.0 x 10 M cadmium nitrate A ^ = 0.242 u = 0.14 pH = 6170 }) = 226.0 mu time (min.) ^t ^t ~ log(A^ - A) 10 1.678 1.436 0.157 60 1.568 1.326, 0.123 90 1.495 1.253 0.098 120 1.481 1.239 0.093 180 1.320 1.078 0.033 210 1.312 1.070 0.029 240 1.259 1.017 0.007 k = 25.3 X 101 - sec. 1 obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 147 _3 p-Methoxybenzeneboronic acid (1.0 x 10 M) Temperature - 90.0°C. Buffer - malonate _3 Added Salt - 1.0 x 10 M cadmium nitrate A 0.061 u = 0.14 pH = 6.70 A = 238.0 mu A^ - A log(A^ - A ^ time (min.) 10 1.490 1.429 0.155 60 1.297 1.236 0.092 90 1.183 1.122 0.050 120 1.107 1.046 0.020 180 0.930 0.869 -0.061 210 0.900 0.839 -0.076 240 0.800 0.739 -0.131 k , - 4 8„. 3 X 10 ^sec. ^ obs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 149 -3 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate -5 Added Salt - 1.0 x 10 M cadmium nitrate A„n y= 0.030 u = 0.14 pH = 6.70 A = 290.0 mu A - A log(A^ - t ime (min. ) t 7.5 0.600 0.570 -0.244 15 0.576 0.546 -0.263 30 0.562 0.532 -0.274 45 0.520 0.490 -0.310 60 0.498 0.468 -0.330 75 0.464 0.434 -0.363 105 0.420 0.390 -0.409 k , = 67.6 X 10 ^sec. ^ obs. kg^ = 4.95 M ^sec. ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 150 _3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Salt - 1.0 x 10 copper(II) nitrate A A^ - A log(A^ - A:^_ time (min.) 5 0.580 0.550 -0.260 10 0.530 0.500 -0.301 15 0.452 0.422 -0.375 20 0.401 0.371 - -0.431 25 0.359 0.329 -0.483 30 0.318 0.288 -0.541 35 0.278 0.248 -0.606 k , = 403 X 10 ^sec. ^ obs. k^^ = 38.5 M ^sec. ^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 151 -3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C, Buffer - malonate Added Salt - 1.0 x 10 copper(II) chloride 0.030 u = 0.14 pH = 6.70 h - 290.0 mu time (min.) ^t ^t ~ log(A^ - A^ 5 0.580 0.550 -0.260 10 0.515 0.485 -0.314 15 0.454 0.424 -0.373 20 0.408 0.378 -0.423 25 0.354 0.324 -0.489 1 r\~^ -1 = 421 X 10 sec. ^obs ..-I -1 - 40.3 M sec. ^Cu. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 152 2,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Salt - 1.0 x 10 copper(II) chloride .-3. 8.90 X 10 M sodium chloride A = 0.030 u = 0.15 pH = 6.70 l\ := 290 .0 mu A. A A log(A^ - A^ time (min.) Of» 5 0.577 0.547 -0.262 10 0.512 0.482 -0.317 15 0.450 0.420 -0.377 20 0.396 0.366 -0.437 25 0.354 0.324 -0.489 30 0.311 , 0.281 -0.551 k = 449 X 10 f'sec. ^ obs k = 43.1 M ^sec. ^ Cu. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 153 _3 2,6-Dlmethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate Added Salt - 1.0 x 10 lead nitrate A_CL;? = 0.030 u - 0.14 pH =6.70 A\ = 290.0 mu log(A^ - t ime (min. ) A\ 10 0.552 0.522 -0.282 20 0.485 0.455 -0.342 30 0.436 0.406 -0.391 40 0.373 0.343 -0.465 51 0.315 0.285 -0.545 60 0.300 0.270 -0.569 70 0.272 0.242 -0.616 k , = 220 X 10 sec. Pb. = 20.2 M ^sec."^ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUN 154 _3 2 ,6-Dimethoxybenzeneboronic acid (4.45 x 10 M) Temperature - 90.0°C. Buffer - malonate _5 Added Salt - 1.0 x 10 M zinc nitrate A = 0.030 u = 0.14 pH =6.70 A 290.0 mu log(A^ - time (min.) ''t - 15 0.583 0.553 -0.257 30 0.550 0.520 -0.284 60 0.526 0.496 -0.3,05 90 0.475 0.445 -0.352 120 0.457 0.427 -0.370 165 0.418 0.388 -0.411 180 0.404 0.374 -0.418 = 36.3 X 10 ^sec. ^ ^obs = 1.82 M ^sec. ^ ^Zn. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.