This dissertation has been 62-830 microfilmed exactly as received

HARRIS, Samuel William, 1930- THE ALKYLATION OF BORON HYDRIDES.

The Ohio State University, Ph.D., 1956 Chemistry, inorganic

University Microfilms, Inc., Ann Arbor, Michigan THE ALKYLATION OF BORON HYDRIDES

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio S tate U n iv ersity

By SAMUEL WILLIAM HARRIS, B. A., M. S.

ii ii ti it 11 tt

The Ohio S tate U n iv ersity 1956

Approved by:

Deparwn^it of Chemistry ACKNOWLEDGEMENT

The author wishes to express his appreciation to

Professors A. B. Garrett and H. H. Sisler for their guidance during the course of this investigation.

He would also like to thank Dr. John Norman of

Olin-Mathieson for the mass spectrographic analysis of one of the compounds prepared.

He would also like to express his appreciation to other members of Research Foundation Project 116-D for the cooperation which was received in various phases of his work. TABLE OF CONTENTS

Page

I . P u rp o s e...... 1

II. Historical ...... 2

A. P rep aratio n 3

B. Chemical P ro p e rtie s 3

C. Structure 6

III. Experimental Techniques ...... 9

A. High Vacuum System 9

B. Experimental Procedures 15

1. Reaction Procedures 15 2. Analysis of the Reaction 18 3. Analytical Methods 22 4. Physical. Characterization 25

C. M aterials 26

IV. Experimental Results ...... 30

A. Reactions of Decaborane 30

1. Friedel-Crafts Reactions 30 2. Grignard Reaction 40

B. Reactions of Pentaborane 40

1. Pentaborane and Methyl Iodide 40 2. Pentaborane and Methyl Chloride 50 3. Pentaborane and Methyl Bromide 51 4. Pentaborane and Ethyl Iodide 52 5. Pentaborane and Ethyl Chloride 60 6. Pentaborane and Ethyl Bromide 61 7. Pentaborane and Methylene Iodide 63 8. Pentaborane and Formaldehyde or Paraformaldehyde 65

i i i TABLE OF CONTENTS (c o n t.)

Page

C. Reactions of sec-But.ylpentaborane 66

D. Reactions of Pentaborane and Methylpenta- borane with Halides . 75

1. Pentaborane and Hydrogen Halides 75 2. Methylpentaborane and Hydrogen Halides 75 3. Methylpentaborane and Methyl Halides 75

V. Discussion and Conclusions ...... BO

A. General 80

B. S tru ctu re 82

C. Theory of Reaction 84

VI. Summary...... 91

Bibliography 93

Autobiography 95

iv LIST OF TABLES

Table Page

I. Reactions of Decaborane with Methyl Iodide ...... 31

II. Reactions of Decaborane with Ethyl Iodide ...... ; ...... 34

III. Reaction of Decaborane with Ethylene ...... 38

IV. Reactions of Pentaborane with Methyl Iodide ...... 43

V. Vapor Pressure of Methylpentaborane-9 ...... 47

VI. Reaction of Pentaborane with Methyl Chloride ...... 51

VII. Reaction of Pentaborane with Methyl Bromide ...... 52

VIII. Reactions of Pentaborane with Ethyl Iodide ...... 54

IX. Vapor Pressure of Ethylpentaborane-9 ...... 58

X. Reaction of Pentaborane with Ethyl Chloride ...... 61

XI. Reaction of Pentaborane with Ethyl Bromide ...... 62

XII. Reaction of Pentaborane with Methylene Iodide ...... 64

XIII. Reaction of sec-Butylpentaborane with Methyl Chloride ... 66

XIV. Vapor Pressure of Methyl-sec-but ylpentaborane 72

XV. Reactions of Pentaborane with Hydrogen Chloride ...... 76

XIV. Reactions of Pentaborane with Hydrogen Halides ...... 77

XVII. Reactions of Methylpentaborane with Hydrogen Halides .... 78

XVIII. Reactions of Methylpentaborane with Methyl Halides 79

v LIST OF ILLUSTRATIONS

Figure Page

1. Structure of Pentaborane ...... 7

2. Structure of Decaborane ...... 8

3 . Vacuum S y stem...... 11

4. Fractionation Train ...... 12

5 . Reaction Vessel ...... 14

6. Tube Opener ...... 14

7. Carbon Dioxide Train ...... 16

8. Infrared Spectrum of Fraction 1, Reactions 19 and 20 ...... 33

9. Infrared Spectrum of Fraction 3> Reactions 19 and 20 ...... 33

10. Infrared Spectrum of Fraction 2, Reactions 21 and 22 ...... 36

11. Infrared Spectrum of Fraction 3> R eactions 21 and 2 2 ...... 36

12. Infrared Spectrum of Decaborane ...... 37

13. Infrared Spectrum of Methylpentaborane ...... 45

14. Infrared Spectrum of Pentaborane ...... 46

15. Vapor Pressure of Methylpentaborane-9 ...... 49

16. Infrared Spectrum of Ethylpentaborane-9 ...... 56

17. Vapor Pressure of Ethylpentaborane-9 ...... 57

18. Infrared Spectrum of Methyl-sec-butylpentaborane ...... 69

19. Infrared Spectrum of sec-Butylpentaborane ...... 70

20. Vapor Pressure of Methyl-sec-but ylpentaborane ...... 74

v i THE A1KYLATI0N OF THE BORON HYDRIDES

I . Purpose

The purpose of this work was the preparation of alkyl derivatives of pentaborane-9 and decaborane.

In planning this work, there was very little previous work to serve as a guide. However, two possible syntheses of alkyl derivatives of pentaborane and decaborane were proposed. They a re :

1. A halogen derivative of the boron hydride was to be prepared and then be reacted with an organom etallic compound

such as the Grignard reagent;

+ nX2 y BioHi4— + BiQHi4_nXn + nRMgX nB^n +

2. A study was to be made of the reaction of an alkyl halide with the boron hydride in the presence of and in the absence of c a ta ly s ts ;

B5H9 + nRX Bsffe^Rn + nHX

B10H14 + nRX sa t B T o H ^ n R n + nHX .

1 II. Historical

The volatile hydroborons were first prepared and characterized by A. Stock"*" and co-workers in the early 1900*s. He reported

1. Stock, A., "The Hydrides of Silicone and Boron," Cornell University Press, Ithaca, New York, 1933. the volatile compounds B2H6, Bi,.Hl0, B5Ife, B5Hn , B6H10 and B ^H ^.

These compounds have the following physical properties.

Name Formula Melting Point Boiling Point

Diborane b2h 6 -165.5 -92.5

Tetraborane B4H10 -120 16

Pentaborane-9 B5H9 -48.6 58

Pentaborane-11 B5Hn -123 65

Hexaborane BgHto -65 —

Decaborane B10Hii* 99.5 213

These volatile hydroborons have aroused a great deal of interest because of their unusual formulas and their chemical properties. Extensive studies have been made on the chemistry of these compounds. This work has dealt chiefly with aiborane and is well summarized by Stock-'-, and in a review by Schlesinger and

Burg^. Most of this work is of only slight interest here, and will

2. Schlesinger and Burg, Chem. Rev.. 31» 1 (1942). not be repeated in detail, but w ill be only summarized, with

2 3 emphasis on the points which are of interest for the present work.

A. Preparation

The modern method for preparation of diborane involves the reduction of boron halides by hydrides such as sodium hydride or lithium aluminum hydride. The other boron hydrides are then pre­ pared from diborane. Tetraborane is the chief product of the slow decomposition of diborane which occurs at ordinary temperatures.

The other boron hydrides are prepared by the pyrolysis of diborane at higher temperatures, the yields of the various hydrides being dependent upon the conditions of the pyrolysis.

B. Chemical P ro p erties

Thermal Stability. The most stable of the hydroborons are pentaborane-9 and decaborane, which do not decompose until temperatures of about 170°C. The other hydroborons decompose at much lower temperatures into other hydrides and hydrogen.

Reducing Agents and Lewis Acids. The hydroborons are very powerful reducing agents. All of them react with oxygen and water at ordinary temperatures, the reaction with oxygen being explosive w ith a l l except w ith decaborane, which re a c ts b u t slowly. Oxygen does not react to give complete oxidation of the boron to boric acid. Reaction with water leads to the formation of hydrogen and boric acid quantitatively if the hydrolysis is carried out for a sufficient length of time. With diborane, hydrolysis is complete in a few seconds, but pentaborane-9 and decaborane require several days at 100°C to insure complete hydrolysis. This reaction is used for analysis of the hydroborons and their derivatives.

The hydroborons react vdth the halogens to replace one or more of the hydrogens vdth a halogen; the number of hydrogens which are

replaced is dependent upon the halogen and hydroboron involved.

The best characterized products are those from diborane and deca­ borane. Diborane vdth chlorine gives boron trichloride, but vdth bromine and iodine, monohalides of diborane are obtained. Deca­ borane with iodine gives a diiododecaborane which has been shown to have the same basic structure as decaborane itself-^. Other higher

3. Schaeffer, R., Abstracts of Papers Presented at the Cincinnati Meeting of the American Chemical Society, 1955 » P» 37Q. iodinated derivatives have been prepared, but these are not as well characterized. Bromo derivatives of decaborane are formed by the action of bromine on decaborane, but these are not as well characterized as the iodo compounds. Monobromo and monoiodo derivatives of pentaborane have been reported^ recently.

4. Schaeffer, R., Shoolery, J. N., and Jones, R., Abstracts of Papers Presented at Atlantic City Meeting of the American Chemical Society, Division of Physical and Inorganic Chemistry, 1956, p. 34R. ______

Diborane reacts with hydrogen bromide and hydrogen iodide at

50 to 1D0° to give halodiboranes and hydrogen, but a catalyst such , '

as aluminum chloride or boron trichloride is required for the

similar reaction of hydrogen chloride. 5 The hydroborons, being coordinately unsaturated, have the ability to act as Lewis acids toward Lewis bases. All of the hydroborons possess this property, but, except in the case of di­ borane, the products are not well characterized. In most cases, diborane simply acts as a source of BH3 groups which coordinate with the Lewis base. The reaction of the higher hydroborons with

Lewis bases usually involves a complete breakdown of the structure.

Alkylations. Prior to the work on this research program at

The Ohio State University, all of the known work on the alkylation of the hydroborons had been carried out on diborane. Burg and

Sc hie singer^ > &,7 prepared the alkyl derivatives of diborane by the

5 . Burs and Schlesinser, J. Am. Chem. Soc., 57, 621, (1935). 6 . Schlesinser, Florin, and Burs, J. Am. Chem. Soc., 61, 1078 (1939). 7 . Schlesinser, Horvitz, and Burs. J. Am. Chem. Soc., 58, A07 (1936). exchange of alkyl groups and hydrogen between trialkylboranes and diborane. Mono, di, tri, and tetra alkyldiboranes were prepared in this manner, but no penta or hexaalkyldiborane could be prepared.

Hurd° has postulated alkyldiboranes as intermediates m the reaction

8. Hurd, D. T., J. Am. Chem. Soc.. 70. 2053 (194#). between diborane and olefins which gives trialkylboranes. Just prior to the work reported here, Mezey? succeeded in

9. Mezey, E. J., M. S. Thesis, The Ohio State University, 1954# preparing sec-butylpentaborane by the reaction of pentaborane with

2-butene at 150°C.

C. S tru c tu re .

The structure of the hydroborons have been determined by modern physical methods. Of interest here are the structures of pentaborane-9 and deeaborane, which are shown in F ig . 1 and 2.

Pentaborane1® has the form of a tetragonal pyramid, and decaborane11

10. Dulmage and Lipscomb, Acta Gryst. , 260 (1952).

11. Kasper, Lucht, and Harker, Acta Gryst.. jj, 436 (1950). is formed from two pentagonal pyramids which share an edge. .

The results of modern quantum mechanical considerations of the electronic structures of the hydroborons have recently been given 12 ,

12. Eberhardt, Crawford, and Lipscomb, J. Chem. Phys.. 22, 989 (1954)• but will be discussed later. B 5 H 9 (Space Relationship)

FIGURE I O Boron o Hydrogen

Structure of Decaborane

FIGURE 2 III. Experimental Techniques

A. High Vacuum System.

Because of the nature of the compounds involved in this work, most of the materials had to be handled in a vacuum system.

Pentaborane had to be handled in a vacuum qjrstemj vacuum line

technique represents the nost convenient way to handle many of the

volatile compounds used in this work.

The principle of vacuum line work is simply that volatile

materials are easily transferred from place to place in a system

if the pressure of non-condensable gases in the system is very

low, i.e. of the order of 10”3 mm of Hg or less. A cooling bath

is placed about the piece of apparatus where it is desired to

collect the material, and the vapors will condense at this point.

At pressures of non-condensable gases of greater than 10“3 mm Hg * vacuum transfer is slow. The volatile compounds should have a

vapor pressure of at least a few mm. Hg at room temperature. If

the vapor pressure is lower than this, vacuum transfers may still

be made if necessary, but they are quite slow. The manner in which

vacuum line technique was used in this work w ill be described in

more detail after a brief description of the vacuum system. A

detailed discussion of high vacuum line work is given by Stock-'-,

9 10

Sanderson^ Mezey^, and Ryschkewitsch^-.

13. Sanderson, R. T., "Vacuum Manipulation of Volatile Compounds", John Wiley and Sons, Inc., Hew York, 1943. 14. Ryschkewitsch, G. E ., Ph. D. Thesis, The Ohio State University, 1955.

The basic requirement for vacuum line work is a system capable

of providing a sufficiently low pressure for the work. The system

used was quite simple, a block diagram being shown in Fig. 3«

Except for the connection of the forepump to the first trap, the

system was constructed of glass with the different parts connected

with high vacuum stopcocks lubricated with Apiezon N grease. The

vacuum was provided by a mercury diffusion pump backed by a

Welch Duo-Seal Vacuum pump.

The units of the system were standard, and need no special

description. The general purpose manifold was constructed of

20 mm. Pyrex tubing to which were connected several 2 mm. high

vacuum stopcocks with 18/9 ball joints for the attachment of other

pieces of equipment.

The fractionation train consisted of six U traps connected in

series. Each trap was connected separately to a manifold so that

entrance could be made at any point in the train. One unit of the

t r a i n i s shown in F ig . 4*

The general purpose manifold, the fractionation train mani­

fold and all of the traps of the fractionation train were cali­

brated with a measured quantity of carbon dioxide. The manometer General Main diffusion purpose Trap manifold Trap manifold pump

Fractionation train Me Leod manifold gauge Trap Fractionation train Fore pump

Vacuum System

FIGURE 3 From preceding To fractionation trap train manifold

1 / To 4 f— next U trQP

Manometer

Section of Fractionation

FIGURE 4 13 corrections were determined simply by measuring the internal diameters of the manometers.

Several other pieces of equipment outside of this system were u sed.

Vapor pressure apparatus. The apparatus used followed closely a design given by Sanderson^. The same apparatus was used for the

15. Sanderson, R. T., ibid., p. 84. determination of molecular weights.

Melting Point Apparatus. The apparatus used for the deter­ mination of melting points was similar to that described by Stock^.

16. Stock, A., ibid., p. 184.

Reaction and Storage Vessels. Almost all of the reactions were run in sealed Pyrex bulbs. These vessels were constructed from round bottomed distilling flasks, and were provided with a con­ densing finger and an inlet tube having a restriction for sealing and a capillary sidearm for removing the reaction products. The inlet tube was usually fitted vdth an 18/9 ball joint for attachment to the vacuum line. Some of the materials used were stored in similar vessels, except that in this case the main body of the vessel was constructed of glass tubing. A typical reaction vessel i s shown in F ig. 5.

Weighing and Storage Vessels. These were constructed of Pyrex tubing connected to a stopcock fitted with an 18/9 ball joint for Reaction Vessel Tube Opener

FIGURE 5 FIGURE 6 15 attachm ent to the vacuum system, and were made so th a t they would fit within the analytical balance.

Tube Opener. For opening th e re a c tio n v essels to the vacuum line, a tube opener such as that shown in Fig. 6 was used.

Toepler Pump. A manual Toepler pump similar to that described by Sanderson^ was used for the measurement of the hydrogen evolved

17. Sanderson, R. T., ibid. , p. 73* by hydrolysis.

Carbon Dioxide Train. For the purification of carbon dioxide during.analysis, a three trap fractionation train and a Vycor tube filled with copper mesh heated with a Cenco combustion furnace were used. This is illustrated in Fig. 7.

Infrared Cells. For liquid samples, standard Baird cells were used. For gaseous samples, a 5*0 cm. cell was constructed by cementing sodium chloride windows to 45 mm. pyrex tubing with

Apiezon wax. A stopcock vdth an 18/9 ball joint was sealed to the glass tubing for admitting the sample.

B. Experimental Procedures.

1. Reaction Procedures.

Almost all of the reactions in this work were run by the pro­ cedure to be described, and unless otherwise stated under the dis­ cussion of the experimental results, this procedure has been used.

The reactions were carried out in the reaction vessels which To vacuum

O'

Manometer

Vycor tube

Calibrated trap

Carbon Dioxide Train

FIGURE 7 17 were described earlier. Any materials which were too slightly volatile to be conveniently introduced into the reaction vessel by vacuum transfer, such as decaborane, aluminum chloride, methylene iodide and nitric acid, were introduced directly into the reaction vessel through the inlet tube before attachment to the vacuum line.

The reaction vessel was then attached to the vacuum line and evacuated, with the condensing finger immersed in a cooling bath if necessary to prevent any of the reactants introduced earlier from b ein g pumped out.

The volatile reactants were then added. If the volatile reagent had a vapor pressure of less than an atmosphere at room temperature, it was added from a storage tube such as previously described, which was weighed before and after the addition. An idea of the approximate amount of m aterial which was added was obtained from an estimate of the liquid volume or from pressure-volume measurements. The addition was made in the following manner: The

storage tube was attached to the system (to which the reaction vessel was also attached), and the system was evacuated. The pump was then closed, the storage tube was opened to the manifold with the condensing tip of the reaction vessel at -196, and the material was condensed into the reaction vessel. If the material had a vapor pressure greater than an atmosphere at room temperature, it was measured by volume in calibrated portions of the system and then introduced into the reaction vessel. After all 18 of the reactants had been introduced, the system was pumped out to remove any traces of non-condensable gases and the reaction vessel was sealed off at the constricted point in the inlet tube. The reaction was then run at the desired temperature in a Fisher

Isotemp oven.

2. Analysis of the Reaction.

After the reaction- had been run at the desired temperature, the capillary tip of the side arm was scratched -with a glass knife, and the sidearm was sealed into the tube opener with Apiezon ¥ wax. The tube opener was then attached to the system and evacuated. The con­ densable contents of the reaction mixture were frozen in the con­ densing tube by immersing it in a liquid nitrogen bath. The pump was closed off, and the capillary sidearm was broken with the tube opener. Any hydrogen present was estimated if desired and then pumped off. The volatile contents of the reaction vessel were then transferred to the fractionation train.

Fractionation was carried out by a process of fractional con­ densation. Cooling baths ivere placed around the traps so that each trap was cooler than the preceding one. The cooling baths were chosen so that one component of the mixture would have a very low vapor pressure at the temperature of the first trap and condense there, while another component would condense at the temperature of the second trap, and so forth. In practice, simple separations such as this were not possible, and refractionation of the fractions was usually necessary. Also in many cases, the components ox the 19 mixture were not known. The condensation temperatures of the various components must then be determined by a tria l and error process. In the fractionation process, time is almost as important

a variable as temperature. Thus a material which will condense at

a certain temperature if the fractionation is done for a short time may pass through a trap at the same temperature if the process is

carried out for a longer period of time. In the fractionation procedure there is considerable choice in the times and temperatures u sed .

In general, if the vapor pressures of two substances to be

separated differs by at least a factor of ten, fractionation is

relatively simple and fairly pure fractions are easily obtained.

If the vapor pressures do not differ by this amount, fractionation

is quite tedious, and pure fractions are not easily obtained.

The following schematic notation was used to represent passing

the material to be separated through traps connected in series.

The temperature of the trap is indicated above the line, and

identification of the fraction, usually by vapor pressure, is shown

below the line. The following example will illustrate the

fractionation procedure. Consider a mixture of A and B, with B 20 having a vapor pressure several times as high as that of A. The fr a c tio n a tio n scheme i s in d ic a ted on page 21.

The material is distilled from trap 1. At first trap 2 is maintained at a temperature such that A w ill condense completely in trap 2. This will require B to partially condense in trap 2. How­ ever, some pure B will pass into the last trap, usually maintained at -196°C„ The pure B is stored elsewhere, and the same fraction­ ation is repeated again on the mixture of A and B obtained in trap 2, the process being repeated until the quantity of B obtained in the last trap no longer makes the process worthwhile. Next, trap 2 is maintained at a temperature such that A will condense without appreciable contamination from B. This will require the last trap to contain a mixture of A and B. The pure A is stored, and the fractionation is repeated as many times as is worthwhile. The mixture of A and B is then subjected to the first, type of fraction­ ation to remove B, after which A is removed again. This is con­ tinued until the fractionation has been completed. We now have quite pure fractions of A and B. However, had the vapor pressures of the materials not differed by enough, A and B would still be impure. Fractionation would have given two fractions, one A-rich and the other B-rich. Further fractionation is then carried out on these, with fairly pure A being obtained from the A-rich fraction and B from the B-rich fraction. The original fractionation is then repeated on the discarded fractions, and'the rest of the process is again repeated. This process is quite tedious, and was carried out 2 1 FRACTIONATION PROCEDU RE

i i

- L t , X T,

T" a + b ~T~f r a c t io n i « " b " repeat s e v e r a l t im e s 1 • - L T2 -I— Tl B “["ADDED^O fraction 1 1 1 _ L T3 X TI n r a + b T FRACTION X 1 M . M 1 A 1 1 1 - L T j _ L T , T added to fraction ^ T 1 " a “ 1I 1 - L T2 X T, T" b " T a ♦ B 1 * ADDED TO I REPEAT 1 1 - L T 3 X T, ADDED TO TL T A + B T V 1 1 REPEAT UNTIL FRACTIONATION IS COMPLETE 22 only for certain important compounds such as the hydroboron derivatives.

The pure fractions obtained were measured by volume or weight,

and were identified by vapor pressure, infrared spectra or chemical

a n a ly s is .

3. Analytical Methods,

a. Oxidation Analysis.

Carbon, boron, and in a few cases iodine were determined by

oxidizing the sample in a sealed vessel with fuming nitric acid at “I f t 200-250°C, according to the method of Schlesinger and Walker .

18. Schlesinger and Walker, J. Am. Chem. Soc.. 57. 621 (1935)•

Two or three days was found to be sufficient to insure complete

oxidation, although a longer time is required when there is a long

alkyl group to be oxidized. Samples which were sufficiently

volatile were introduced into the oxidation vessel by vacuum trans­

fer. Otherwise, the samples were sealed into pre-scratched, long,

thin-walled capillary tubes which were introduced into the

oxidation vessel through the inlet tube. With the nitric acid

frozen the capillary tube was broken by breaking it against the

walls of the oxidation vessel. If the nitric acid were not frozen

o u t, an explosion was lik e ly to r e s u lt when the sample came in to

contact with the nitric acid.

After oxidation was complete, the analysis was worked up in

the train showed earlier. The first trap was held at -119°C, and 23 trapped everything except carbon dioxide, nitric oxide, and nitrous acid, which condensed in the second trap at -196°C. The nitric oxide was pumped off, and the nitrous oxide was decomposed by passing it over hot copper. The carbon dioxide was measured by p re ssu re in a known volume.

The boric acid was washed out of the reaction vessel and ti­ trated with standard base in the presence of mannitol. Any strong acid was first neutralized to a pH of 5*5 to 6.0, mannitol was added, and the titration was continued until the boric acid end­ point. This varied somewhat depending upon the amount of mannitol present, but was at about 8 . 2 .

When iodine was present in the sample, it was obtained from the oxidation as free iodine. It was separated from dinitrogen tetroxide by distillation of the dinitrogen tetroxide and then was separated from the nitric acid solution by extraction with carbon tetrachloride. A slightly acid aqueous solution of potassium iodide was added to the carbon tetrachloride solution of iodine, and the iodine was titrated with a standard solution of sodium thio- s u lf a te .

b. Hydrolysis

Hydrogen, iodine, and chlorine were determined by hydrolysis of the sample in a sealed vessel. For decaborane and pentaborane derivatives, a temperature of 1$0°C and several days reaction time was necessary to insure complete hydrolysis, but with boron tr i­ chloride or alkylhaloboranes, hydrolysis was easily effected in a 24 few minutes at room temperature.

I t has been shown th a t hydrolysis does not ru p tu re the boron-carbon bond‘d . The hydrolysis of an alkylpentaborane would

19. Schlesinger, Florin, and Burg, J. Am. Chem. Soc.. 61. 1078 (1939). ______go according to:

B5H8R + 14H20 ►4H3BO3 + RB(0H) 2 + 11H2 .

The hydrolysis of a rnonoalkylaecaborane would go as*

B1oH13R + 29H20 ► 9 H3BO3 + RB(0H) 2 + 21H2 .

Similarly, a dialkyldecaborane would give:

b ioh12r 2 + 28H20 ► 8 H3BO3 + 2RB(0H) 2 + 20 H2 .

In the titration of the boric acid, all of the boric acid and a part of the alkyl boric acid is titrated. Hence the results of the boric acid analysis from hydrolysis are rather inconclusive.

The hydrogen produced by the hydrolysis was measured with the

T oepler pump and checked w ith th a t c alc u la te d fo r the compound in q u estio n .

In one case where a pentaborane derivative contained iodine, hydrolysis produced hydrogen iodide, which was titrated with base.

In general for pentaborane and decaborane derivatives, analysis by hydrolysis did not give much information, and so was not extensively used.

Alkyl haloboranes and boron trichloride are easily hydrolyzed to give a hydrogen halide and a boric acid, both of which may be 25 determined by titration with a pH meter, tfydrolysis was extensively used on fractions which were believed to contain these compounds.

k * Physical Characterization.

a. Infrared Spectra.

The samples were introduced into the cells described earlier and the infrared spectra were taken on a Baird spectrophotometer.

The spectra were compared with those of known compounds.

b. Vapor Pressure.

For the determination of vapor pressure below room temperature, a bath of the proper temperature was placed around a bulb or trap containing the sample, and the pressure was measured on a manometer in the system. This was done very extensively in following fractionations.

For the measurement of vapor pressures above room temperature, the apparatus described earlier was used. The sample was condensed into the bulb which had been previously baked out. The mercury level was then raised to the desired point in the null gauge, which also served to isolate the sample from the remainder of the system. The whole apparatus was then immersed in a bath of water or silicone oil which was heated with a Genco knife heater. The vapor pressure of the sample at any given temperature was deter­ mined by adjusting the null gauge to zero by admitting dry nitrogen to the manifold to which the null gauge was connected and reading the pressure in the manifold. 26

c. Molecular Weight.

Molecular weights were determined in the same apparatus used for vapor pressure measurements. The bulb was calibrated by measurement of the pressure of a known amount of carbon dioxide.

The molecular weight was determined from the ideal gas law by measuring the pressure a given weight of sample produced in the b u lb .

d. Melting Point.

The melting point was determined in the apparatus described earlier. The inner tube was raised with a magnet, a sample was frozen out just below it, and the tube was lowered so as to rest on the sample. A bath was placed around the apparatus, and the melting-point taken as the temperature at which the sample loosened enough for the inner tube to drop.

C. M aterials

Pentaborane. Pentaborane was supplied by Olin-Mathieson and was used without further purification.

Decaborane. Decaborane was supplied in a kerosene solution by Olin-Mathieson. The solution was distilled, with the deca­ borane co-distilling with the first half of the distillate. The decaborane was removed from the distillate by crystallization at

-78 followed by filtration. The decaborane was then recrystallized from a hydrocarbon solvent such as a Skellysolve.

sec -Butyloentabo rane. sec -But.vlpent aborane prepared by a 27 reaction between 2-butene and pentaborane^ was supplied by

Edward Hasely of The Ohio State University Research Foundation

Project 116-D.

Alkyl Halides. All of the alkyl halides used were obtained commercially, and were used without further purification except for drying over phosphorus pentoxide.

Methyl iodide. Eastman Organic Chemicals.

Ethyl iodide. Coleman and Bell, C. P.

Methylene iodide. Eastman Organic Chemicals.

Methyl bromide. Dow. Technical.

Ethyl bromide. Eastman Organic Chemicals.

Methyl chloride. DuPont. Technical.

Ethyl chloride. Dow, U. S. P.

Hydrogen Halides.

Hydrogen chloride. Matheson, anhydrous. For some runs,

i t was prepared by the action of sulfuric acid on sodium chloride,

and purified by passing it through a - 140° tra p .

Hydrogen bromide. Matheson,. anhydrous. For some runs,

i t was prepared by the action of sulfuric acid on sodium bromide,

and purified by passing it through a - 140° tra p .

Hydrogen iodide. This was obtained from a reaction between

methyl iodide and decaborane, and was purified by fractionation.

Aluminum Chloride. Reagent grade, sublimed aluminum chloride

from the General Chemical Division, Allied Chemical and Dye Company 28 was used. For most of the reactions, this was used without further purification. However, for the reactions of the hydrogen halides with pentaborane, and for all of the reactions involving methylpentaborane, it was resublimed. Aside from working as quickly as possible and keeping exposure to the atmosphere at a minimum, no special precautions were taken to exclude moisture.

Boron Trifluoride. Matheson, anhydrous.

Ethylene. Matheson, C. P.

Several materials were required for the cooling baths re­ quired in this work. The following materials were used to provide the indicated temperatures.

Material Temperature

Ice-Water 0°C.

Carbon Tetrachloride Slush -23°

Ethylene Chloride Slush - 36°

Chloroform Slush - 63°

Carbon Tetrachloride-Chloroform 0° to -78.5

Dry Ice, Carbon Tetrachloride- Chloroform Slurry -78.5

Methylene Chloride Slush -97

Ethyl Ether Slush -116

Ethyl Bromide Slush -119

Methylcyclopentane Slush -142

Liquid Nitrogen -196 29

The materials used as slushes were frozen with Dry Ice if they froze above -78. If they froze below -78, liquid nitrogen was used as the freezing agent. A mixture of chloroform and carbon tetrachloride, cooled to the desired temperature with Dry

Ice, was found to be an excellent coolant, since any temperature above -78 could easily be provided. This coolant required little more attention than was needed for the slushes. IV. Experim ental R esu lts

A. Reactions of Decaborane

1. Friedel-Crafts Reaction.

As discussed earlier, the purpose of this work was the preparation of alkyl derivatives of pentaborane -9 and decaborane.

An attempt was made to do this through a simple exchange of a hydrogen atom for an alkyl group of an alkyl halide, but this was not successful. However, it was found that aluminum chloride served as a catalyst for the reaction, and alkyl derivatives of decaborane were easily prepared from alkyl halides if a small amount of aluminum chloride was used as a catalyst.

Details of how the reactions were run were described earlier.

Weighed amounts of aluminum chloride and decaborane were introduced into the reaction vessel before placing it on the vacuum line where the alkyl halide was added, and the vessel was sealed off. After reaction the vessel was sealed into the tube opener and attached to the vacuum line. The easily transferable products were transferred to the fractionation train for fractionation. The relatively non~ volatile decaborane and its derivatives were dissolved in a hydro­ carbon solvent and filtered to remove aluminum chloride, after which the solvent was distilled off. The decaborane and its derivatives were then distilled from a small still. No special precautions were taken in this work to exclude moisture and oxygen except that

30 31 exposure of the material to the atmosphere was kept to a minimum.

The products were identified by oxidation analysis giving the carbon and boron content.

The results of these reactions are given below,

a. Decaborane and Methyl Iodide.

Table I

Reactions of Decaborane with Methyl Iodide

Reaction 19 Reaction 20 Reaction 34

B10Hi4 2 0 .3 mmoles 20.4 mmoles 35»4 mmoles

ch 3i 53*1 mmoles 60.0 mmoles 39.0 mmoles

A id 3 3 .4 mmoles 3 .4 mmoles 3 .8 mmoles

Temp. 100° C 100° C 100°C

Time 24 hr s. 24 h rs. 24 h rs.

V o la tile Products.

CH* Identified by vapor pressure from all reactions, but not measured.

HI 4 6 .1 mmoles 52.6 mmoles 30.6 mmoles

The derivative fractions from reactions 19 and 20 were com­ bined and distilled. The following fractions were obtained. Any analyses carried out are indicated. 32

Fraction 1 Fraction 2 F rac tio n 3

Boiling Range 80-85°C 85 - 86 °C app. 100°C

P ressu re 5 mm 5 mm le s s th an 0.5 ram

In fra re d F ig . 8 ------F ig . 9

Boron 69.3 1o ------50.5 1o

Carbon 18.4 1° 17.2 io

Io dine None ------1 3 .8 $

B*. C*. I B1oG2.^ BiqOs . i ^o . z

The in fra re d spectrum of decaborane i s shown in F ig . 12 fo r

comparison.

The derivative fraction from reaction 34 was distilled. The

following fractions were taken. Any analyses are shown.

Fraction 1 Fraction 2 Fraction 3

Boiling Range 76-78°C 78-81°C above 81°G

Pressure 5 ram 5 mm less than 0.5 am

Boron 75 .6------

Carbon 11.8 ------

BjC B io ^i.^ ------Percent Transmittance Percent Transmittance 100 100 20 0 6 80 0 4 20 0 6 0 4 80 - F ig s. s. ig F g. : acton n tio c ra F 9: . ig F F ig . . ig F 8 8 Frcton 1 Recin 1 ad 20. and 19 eactions R 1, n tio rac F : and 9*. In fra re d Spectra of M ethyldecaboranes. ethyldecaboranes. M of Spectra d re fra In 9*. and 3> atos 9 n 20. and 19 eactions R ae egh n Microns in Length Wave ae egh n Microns in Length Wave IUE 8 FIGURE IUE 9 FIGURE 34 b. Decaborane and Ethyl Iodide,

Table I I

Reactions of Decaborane with Ethyl Iodide.

Reaction 21 Reaction 22 Reaction 35

Bio Hia - 21.6 mmoles 19.8 mmoles 37.4 mmoles

c 2h 5i 65.6 mmoles 63.8 mmoles 40.5 mmoles

A1C13 3.5 mmoles 3 .8 mmoles 3.8 mmoles

Temp. 100°C 100°C 100°C

Time 24 h rs. 24 h rs. 31 h rs.

Volatile Products.

c 2h 6 1 0 .9 mmoles 1 4 .4 mmoles 7 .8 mmoles

h i 59.8 mmoles 54.5 mmoles 36.4 mmoles

HC1 1 .2 mmoles 2 .0 mmoles 1 .6 mmoles

An attempt was made to use boron trifluoride or a mixture of boron trifluoride and boron trifluoride-ethyl etherate as the catalyst in a reaction of decaborane with ethyl iodide. This attempt was unsuccessful, and no reaction occurred even at 125°C.

The derivative .fractions from reactions 21 and 22 were combined and distilled. The following fractions were taken, with the analyses indicated. 35

F ra c tio n 1 2 3 4 B o ilin g 100°C- 115°C- 130°C- above Range 115 °C 130°C 135 ®C 130°C

P ressu re 5 mm 5 mm 5 mm 5 mm

In fra re d ------F ig . 10 F ig . 11 ------

Boron ------55.6# ------42.5#

Carbon ------28.0# ------27. 8 #

Iodine ------8,9# ------B iC :I B10B4.5 B10C5. Tq.2

The following fractions were taken from the distillation of the derivative fraction of reaction 35* The analyses carried out are indicated.

F ra c tio n 1 2 3 4

B o ilin g 85 °C- 96°C- 85°C- Did not Range 92° C 103°C • 95°G • d i s t i l l

P ressu re 5 mm 5 mm 0 .5 mm ------

Boron ----- 6 8.5# ------58 . 1#

Carbon ----- 18.0# ------14.3#

Io d in e ----- 1 . 2# ------12. 6#

B jC tl ----- B10C2. 4^0.01 B10C2. 2lo .2 Percent Transmittance Percent Transmittance 100 100 20 0 8 0 6 80 40 60 40 20 g. 0 Fr i , atos 1 n 22. and 21 eactions R 2, n tio c ra F 10: . ig F F ig. ig. F gs 1 ad 1 I r ed Spcr o Sthylaecaboranes. S of pectra S d re fra In 11: and 10 s. ig F : U aton 3 Recin 2 ad 22. and 21 eactions R 3> n ractio F ae egh n Microns in Length Wave ae egh n Microns in Length Wave IUE 10 FIGURE IUE II FIGURE Percent Transmittance 100 0 6 0 4 20 0 8 nfae pcrm f Decaborane of Spectrum frared In ae Lnt i Microns in Length Wave. IUE 12 FIGURE 33 c. Decaborane and Ethylene

Table I I I .

Reaction of Decaborane with Ethylene.

Reaction 50

Bl0 Hl4 16.1 mmoles

0ziW 76.0 mmoles

A1C13 5.5 mmoles

Temp. 100° C

Time 5 h rs .

C2H4. recovered 45.6 mmoles

No other fractions of high volatility were obtained.

The following results were obtained from the distillation of the derivative fraction. Any analyses are indicated.

F ra c tio n 1 2 3

B oilin g 85- 95- 102- Range 95<>.C 102°C 110°C

P ressu re 5 mm 5 mm 5-1 mm

Boron ------6 8 . 2$ ------

Carbon ------19.8% ------

BtC ------B10C2. 6

d. Discussion.

This research indicates that alkyl iodides and ethylene react with decaborane in the presence of aluminum chloride to form a 39 mixture of alkyl derivatives of decaborane. The analyses indicate that a mixture of mono-, di-, and tri- alkyl derivatives of deca­ borane are formed. The presence of iodine in some of the samples must be regarded as due to some trace amount of impurity because of th e smal 1 amount p re sen t.

The yield of the reaction is difficult to estimate because quantitative separation of the products is not feasible. The boiling points of the different derivatives are too close and the amounts involved in this work were too small to permit any degree of separation with the apparatus used. However, the amount of hydrogen iodide obtained from the reaction indicates that the amount of alkylation is of the order of 80-90 per cent of the alkyl iodide introduced. There is very little decomposition of the decaborane in the reaction.

The r e la tiv e amounts of th e mono- and polyalkylated products can be changed somewhat by varying the ratio of alkyl iodide to decaborane, but a mixture of different products was always obtained in this work. Polyalkylated products were obtained even with a

1 :1 mole ratio of reactants.

The alkylated decaboranes were all colorless liquids when first obtained. These liquids could not be crystallized, but froze into a glass at low temperatures. However, some of the liquids crystallized after standing at room temperature for several months.

It seems probable that pure derivatives may be crystalline 40 compounds; but the mixtures, obtained in this work, were impossible to crystallize.

2. Grignard Reaction.

An attempt was made to prepare an alkyl derivative of deca­ borane through the following reactions:

+ 2 la “ “ —►B i 0Hi 2I 2 + 2 HI

B1oH12I 2 + 2RMgX ------► B10H12R2 + 2MgXI .

Decaborane was reacted with iodine in a sealed vessel. The iodine reacted completely, yielding hydrogen iodide and a brownish yellow solid residue. This residue was extracted with ether, and the ether solution was filtered into a flask containing an ethereal solution of ethyl magnesium iodide. A reaction took place almost immediately to give a heavy, viscuous oily material which settled to the bottom of the reaction vessel. This oily residue was not appreciably soluble in carbon tetrachloride, Skellysolve, benzene, ether, or carbon disulfide. Evaporation of the ether solution gave no products. The solubility characteristics of the oily material were not those to be expected of a decaborane derivative, and this work was abandoned in favor of the more promising Friedel-

Crafts synthesis.

B. Reactions of Pentaborane.

1. Pentaborane and Methyl Iodide.

In the reaction of pentaborane with methyl iodide, all reactants and products were handled as previously described. 41 The reaction of methyl iodide and pentaborane in the presence of aluminum chloride gave methylpentaborane-9. A temperature of 90-

100° was required to make the reaction go at an appreciable rate.

At these temperatures, a reaction time of 3-24 hours is necessary.

The longer time makes it possible for the reaction to go further to completion, but it also increases the amount of decomposition. The reaction products varied somewhat from reaction to reaction, but in­ cluded hydrogen, hydrogen iodide, methane, boron trichloride, tri- m ethylborane, an u n id e n tifie d iodine containing compound w ith a vapor pressure of 2.7 nnn at 27°C, methylpentaborane-9, and a con­

siderable quantity of non-volatile tars which possessed a hydridic

c h a ra c te r. The amount of ta r form ation seemed to be reduced some­ what by adding mercury to the reaction. The mercury also removed

an u n id e n tifie d iodine containing compound which otherw ise would have reacted with mercury in the manometers and traps in the vacuum

system .

Hydrogen was identified by its presence as a non-condensable

gas; methane by its vapor pressure at -1965 boron trichloride by its

infrared spectra, and by hydrolysis into boric acid and hydrochloric

acid; and trimethylborane by its infrared spectra.

Methylpentaborane was identified by oxidation, hydrolysis, and

infrared spectrum. Its infrared spectrum was consistent with what

would be expected for such a compound. 42

The analysis gave the following results for the sample used.

Element Theoretical for Found CH3B5H3

Boron 70.07 $ 70.5 $

Carbon 15.57 $ 15.5 1o

Hydrogen 6.36 mmoles. 6.62 mmoles.

B:C ^5 . 0 0 ^ . 9 9

The results of the analysis clearly indicated that the material was methylpentaborane.

Because the vapor pressure of methylpentaborane is not very different from that of the reactants it was not possible by fractionation alone to obtain a sample of methylpentaborane pure

enough for vapor pressure measurements. But a pure sample was

prepared in the following mannerI The most likely impurities

in methylpentaborane were the reactants, pentaborane and methyl

iodide. Methylpentaborane, purified as much as practical by

fractionation, was reacted with methyl iodide to remove any re­ maining pentaborane. The excess methyl iodide was then separated

from methylpentaborane by fractionation to the greatest possible

degree. The methylpentaborane thus obtained was reacted with

mercury to remove any remaining methyl iodide. Methylpentaborane

purified in this manner was used for the determination of its

vapor pressure, melting point, and molecular weight. 43 Some typical reaction data are given in Table IV.

Table IV

Reactions of Pentaborane and Methyl Iodide.

R eactio n 52 57 58

B5H9 34.0 mmole 32.5 mmole 38.0 mmole 48.0 mmole

CH3I 72 .8 mmole 4 9 .1 mmole 63.3 rmaole 6 2 .2 mmole

AICI3 1 .9 mmole 5 ,3 mmole 6 .9 mmole 5 .4 mmole

Hg. Absent P resent P resent P resen t

Time 6 h rs . 3 h rs. 40 h rs. 40 h rs .

Temp. 100°C 100°C 100°C 100°C

V essel 1000 cc 1000 cc 1000 cc 1000 cc Size

R eaction P roducts

CH3B5H8 21.5 mmole 18.9 mmole 16.7 mmole 19.9 mmole

B5H9 None mmole 3.3 mmole 1 2 .2 mmole None

gh 3i 33*3 mmole 12.5 mmole None None

H2 29 mmole 32 mmole 32 mmole 24 mmole

HI 6 mmole None None None

BCI3 (a) 7.2 mmole 4 .6 mmole 1 .0 mmole

B(CH3) 3 (b) (b) (b) 0 .7 7 mmole

GH4. P resent (c) (c) (c)

a. Boron trichloride was not identified as a product from

this reaction, but the fractionation data does not exclude its

I 44 p resen ce.

b. Trimethylborane was not identified from these reactions, but the fractionation data does not exclude the possibility that a small quantity may have been present.

c. The possibility that methane may have been present was not checked.

Physical Properties of Methylpentaborane-9.

At ordinary temperatures, methylpentaborane-9 ia a colorless liquid with the following physical characteristics:

1. Infrared spectrum. The infrared spectrum of gaseous methylpentaborane is given in Fig. 13* This spectrum may be com­ pared to that of pentaborane-9 given in Fig. 14.

2. Vapor pressure. The vapor pressure of methylpenta­ borane-9 was determined over the range -31*3 to 75»5°C« The vapor pressure was found to fit the equation

loSPm ' -;L-71i * JP3 * 7.80.

The average heat of vaporization over this range is 7>820 cal/mole.

Interpolating on a plot of log p versus l/T over the temperature range 66 to 75. 5°C gives the normal boiling point as 75.2°C. The h e a t of v ap o rizatio n over t h i s range i s 7>480 cal/m ole. The

Trouton constant is 21.5 e«u* The vapor pressure data for methyl­ pentaborane-9 is given in Table V, and the curve for log p^ versus l/T is given in Fig. 15. Percent Transmittance 100 20 80 0 4 60 nfar pcrm f ethylpentahorane M of Spectrum d re fra In ae egh n Microns in Length Wave IUE 13 FIGURE Percent Transmittance 100 60 40 80 20 nfae pcrm f Pentaborane of Spectram frared In ae egh n Microns in Length Wave IUE 14 FIGURE Table V

Vapor Pressure of Methylpentaborane-9

Temperature P ressure o O

O l/T x 10 3 mm Hg

-3 1 .3 241.9 4.134 5.3 -2 8 .5 244.7 4.087 5.9 -2 5 .5 247.7 4.037 8.3 -21.5 251.7 3.973 11 .2 -16.5 256.7 3.896 13.6 -1 1 .5 261.7 3.821 18.4 - 7.5 265.7 3.764 23.7 - 4*3 268.9 3.719 27.9 - 2 .1 271.1 3.687 31.6 • 0 .1 273.3 3.659 35.2 2.5 275.7 3.627 39.4 3.5 276.7 3.614 42.6 5 .8 279.0 3.584 47.9 8 .4 281.6 3.551 56.4 11.0 284.2 3.519 63.O 12.3 285.5 3.503 67.7 1 4 .2 287.4 3.479 74.5 15.5 288.7 3.464 78.3 17.3 290.5 3.442 84.6 18.7 291.9 3.425 90.7 20.9 294.1 3.400 97.0 22.5 295.7 3.382 106.3 24.9 298.1 3.355 116.8 27.0 300.2 3.331 128.0 29.3 302.5 3.306 139.6 31.4 304.6 3.283 152.7 32.9 306.1 3.267 164.3 34.8 308.0 3.247 177.9 36.3 309.5 3.231 190.4 38.0 3 H .2 3.213 205.2 39.7 312.9 3.196 219.5 41.3 314.5 3.180 237.5 44.2 317.4 3.151 265.5 288.2 46.3 319.5 3.130 321.6 3.109 312.3 48.4 335.2 50.3 323.5 3.091 325.7 3.070 363.1 52.5 386.8 54*4 327.6 3.052 56.9 330.1 3.029 422.4 60 .0 333.2 3.001 459.1 m

Table V (cont.)

°c °K l/T x 10 3 P ressure

61.7 334.9 2.985 493.5 6 4 .2 337.4 2.963 537.2 6 6 .7 339.9 2.942 580.6 68.8 342.0 2.923 621.5 71.1 344.3 2.904 661.1 72.9 346.1 2.889 707.3 7 4 .3 347.5 2.877 741.7 75.5 348.7 2.867 769.7 Cooling Curve

75.5 348.7 2.867 769.7 74.3 347.5 2.877 742.6 72.9 346.1 2.889 710.4 71.4 344.6 2.901 676.4 69.2 342.4 2.920 6 21.0 66.7 339.9 2.942 585.4 64.8 338.0 2.958 548.4 61.2 334.4 2.990 486.5 57.3 330.5 3.025 428.7 53.4 326.5 3.062 375.8 50.9 324.1 3.085 343.8 48.3 321.6 3.109 313.5 44.9 318.4 3.141 273.6 41.4 314.6 3.179 237.5 37.7 310.9 3.216 203.6 33.4 306.6 3.262 1 68.0 29.8 303.0 3.300 143.7 24.0 297.2 3.365 112.8 19.8 293.0 3.413 95.2 13.9 287.1 3.483 73.5 8.8 282.0 3.546 57.7 3.4 276.6 3.615 42.7 0.1 273.3 3.659 35.0 - 4*6 268.6 3.723 26.9 20.8 - 9.5 263.7 3.792 -1 7 .0 256.2 3.903 13.0 3.960 10.4 -2 0 .7 252.5 6.8 -2 6 .3 246.9 4.050 5.3 -34*3 238.9 4.186 49

2.8

2 .4 -

2.0 -

mm

23 3.23.4 3 .6 3.8 4.0 4 .2 l/T x I03

FIGURE 15

J& vor Pressure of Methylpentaborane 50

3. Melting point. The melting point of methylpentaborane-9 was found to be -56 to - 55°C.

4. Molecular weight. The molecular weight of the sample was determined by gas density measurements to be 78*2. The theoretical value is 77. 20.

2. Pentaborane and methyl chloride.

Methyl chloride was found to react with pentaborane in the presence of aluminum chloride to give methylpentaborane. This reaction went with much greater facility than did the reaction with methyl iodide. While no reaction took place in 16 hours at -25°C, or in 5 hours at 0°C, the reaction went very readily at room temperature, and was virtually complete after standing at room temperature for 48 hours. The products of the reaction included hydrogen, diborane, methylpentaborane, methyldichloroborane, and a considerable quantity of a non-volatile, hydridic tarry residue.

Hydrogen was identified by its presence as a non-condensable gas. Diborane and methylpentaborane were identified from their vapor pressures and infrared spectra. There is a possibility that

hydrogen chloride was present in the diborane fraction since this

would n o t have shown in th e in fra re d s p e c tra . The diborane was not

hydrolyzed, so no statement may be made on the presence of hydrogen chloride among the products of the reaction. Methyldichloroborane was identified by hydrolysis and from a comparison of its infrared

spectra with that of ethyldichloroborane.

The results of a reaction between pentaborane and methyl 51 chloride are given in Table VI.

Table VI

Reaction of Pentaborane with Methyl Chloride

R eaction 54

B5Hq 38 .8 mmoles

CH3C1 41.5 mmoles

AICI3 4 .1 mmoles

Time 48 hr s.

Temp. 25°C

Vessel Size 1000 cc.

P roducts

BaHg, I3.5 mmoles (P art may have been HC1.)

H2 11 mmoles

CH3B5Hg 19*5 mmoles

CH3BCI2 7 mmoles

3. Pentaborane and methyl bromide.

Methyl bromide was also found to react with pentaborane in the presence of aluminum chloride to yield methylpentaborane.

This reaction also went with much greater facility than did the reaction of methyl iodide. No variation of reaction conditions was tried, but the one reaction ran went almost to completion after three days standing at room temperature. Products of the reaction included hydrogen, diborane, methane, methyldichloroborane, methylpentaborane, and large amounts of hydridic, non-volatile m aterials. A bromomethylborane may have been present, but was not

identified. The yield of the products was difficult to estimate because of difficulties involved in the fractionation. The results

of the reaction which was run are given in Table VII.

Table VII

Reaction between Pentaborane and Methyl Bromide

Reaction 53

B 5 H 9 37.5 mmole

CH3Br 44.5 mmole

AICI3 3 .7 mmole

Time 72 h rs .

Temp. 25°C

Vessel Size 1000 cc

Products

h 2 27 mmole

CH*. Not measured

CH3BCI2 1 mmole

0 .8 mmole

ch3b5h8 27 mmole

4. Pentaborane and ethyl iodide.

The reaction of ethyl iodide with pentaborane in the

presence of aluminum chloride was similar to the reaction of methyl iodide with pentaborane. A temperature of 80-100°C and several

hours was necessary for the reaction. Products of the reaction in­

cluded hydrogen, ethane, boron trichloride, ethylpentaborane,

hydrogen iodide, and a considerable amount of hydridic, non-volatile

m a te ria ls.

The identification of the products was made as described

earlier, except that ethane was identified from its vapor pressure

and inertness toward water. This did not exclude the presence of

ethylene, but the latter's reactivity with pentaborane excludes it.

The oxidation analysis of ethylpentaborane gave the following

r e s u lts .

Element Found Theoretical for

f0 Boron 57*7 59.3

$ Carbon 25.4 26.3

B:C B5.00C1.99

An attempt was made to use boron trifluoride as a catalyst

for this reaction, but it was found that no detectable reaction

occurred if boron trifluoride was used, even at 100°C.

The purification of ethylpentaborane for physical constant

measurements was carried out in the same manner as described

earlier for methylpentaborane. However, the purity of the final

product is more doubtful. A possible product of the reaction is

triethylborane. This was never found, but small amounts of tri-

methylborane were found in the reactions of methyl iodide and 54 small amounts of triethylborane might be expected from the reaction of pentaborane and ethyl iodide. Because of the proximity of the values of the vapor pressures, it is impossible to fractionate

ethylpentaborane from triethylborane, and no chemical separations are possible. Center cuts of the ethylpentaborane fraction were

taken for all physical measurements.

Some typical reaction data are given in Table VIII.

Table V III

Reactions of Pentaborane-9 with Ethyl Iodide.

Reaction 12 Reaction 28

B5H9 30.1 mmoles 44.6 mmoles

G2H5I 29*5 mmoles 29.5 mmoles

A1C13 1.6 mmoles 3.5 mmoles

Temp. 80° C 100° C

Time 16 h rs. 15 h rs.

Vessel Size 1000 cc 1000 cc

Products

h 2 11 mmoles 44 mmoles

C2H6 5 .2 mmoles 8.6 mmoles

HI Net id e n tifie d 3.0 mmoles

BCI3 Not id e n tifie d 2.0 mmoles

B5H9 Not measured 1 3 .1 mmoles

C2H5B5Hs 9.6 mmoles 9.1 mmoles 55 Physical Properties of Ethylpentaborane-9.

At ordinary temperatures, ethylpentaborane-9 is a colorless liquid having the following characteristics:

1. Infrared spectrum. The infrared spectrum of a gaseous sample of ethylpentaborane is given in Fig. 16.

2. Vapor pressure. The vapor pressure of ethylpenta­ borane-9 was determined over the range 0° to 110°C. The vapor pressure over this range was found to fit the equation

, . - 1.83 x 103 . „ , „ lo S Pmm . t 7,42 *

The heat of vaporization over this range is 8,370 cal/mole. Inter­ polation on a plot of log p versus l/T over the range 92-106°C gives the normal boiling point as 105. 8 °C. The heat of v ap o rizatio n over this range is 3,140 cal/mole. The Trouton constant is 21.5 e .u .

The vapor pressure for ethylpentaborane is given in Table IX, and the plot of log pmTn against l/T is given in Fig. 17.

3. Melting point. The melting point of ethylpentaborane was found to be -85°C.»

4. 1-folecular weight. The molecular weight of ethyl­ pentaborane was determined to be 93.8. The theoretical value is

91.22 . Percent Transmittance 100 20 0 4 0 6 80 nfae pcrm f thylpentaborane-9 E of Spectrum frared In ae egh n Microns in Length Wave IUE 16 FIGURE 0 s 57

2.8 Vapor Pressure of Ethylpentaborane -9

2.6

2.4

2.2

2.0 mm

2.6 2.8 3.0 3.4 3.6 3 83.2 x I0 3

FIGURE 17 58

Table EL

Vapor Pressure of Ethylpentaborane-9 1

Temperature P ressure °G °K l/T x 103 mm Hg

0 .1 273.3 3.658 8 .8

5.1 278.3 3.593 11.3

9.8 283.0 3.533 15.3

14.6 287.8 3.474 20.6

19.4 292.6 3.417 27.1

24.4 297.6 3.360 34.6

29 .8 303.0 3.300 4 6 .2

40.1 313.3 3.191 74.5

44.9 318.1 3.143 91.6

50.6 323.8 3.088 116.5

54.7 327.9 3.049 136.6

59.8 333.0 3.003 167.7

65.O 338.2 2.956 203.2

70 .1 343.3 2.912 244.6

75.3 348.5 2.869 293.4

80.1 353.3 2.830 345.5

85.6 358.8 2.787 413.8

90.5 363.7 2.749 473.2

95.4 368.6 2.712 562.2

100.4 373.6 2.676 652.8 59

Table IX (c o n t.)

Temperature P ressure °C °K l/T x 10 3 mm Hg

104.6 377.8 2.646 735.6

106.4 379.6 2.634 774.6

106.4 379.6 2.634 774.6

104.9 378.1 2.644 743.0

103.2 376.4 2.656 711.3

101.7 374.9 2.667 678.7

100.0 373.2 2.679 6 4 6 .1

97.8 371.0 2.695 603.9

94.7 367.9 2.718 551.1

92.6 365.8 2.733 517.2

90.0 363.2 2.753 476.9

87.4 360.6 2.773 440.1

84.7 357.9 2.794 402.5

79.9 353.1 2.832 342.6

74.7 347.9 2.874 288.6

69.0 342.2 2.922 237.4

64.5 337.7 2.961 200.1

59.6 332.8 3.004 167.6

54.6 327.8 3.050 137.9

49.7 322.9 3.096 113.7

45.3 318.5 3.139 94.5 60

Table IX (cont.)

Temperature 4 Pressure °C °K l/T x 10 3 ram Hg

39.7 312.9 3.195 75.0

34.3 303.0 3.246 59.9

29.0 302.2 3.309 46.5

24.9 298.1 3.354 38.1

20.1 293.3 3.409 30.9

15.0 288.2 3.469 23.6

10.1 283.3 3.529 18.8

0 .1 273.3 3.658 11.7

5. Pentaborane and ethyl chloride. Ethyl chloride reacted readily -with pentaborane in the presence of aluminum chloride to give ethylpentaborane; the reaction went easily at room temperature. Products of the reaction in­ cluded hydrogen, hydrogen chloride, ethane, diborane, boron tr i­ chloride, ethyldichloroborane, ethylpentaborane, and large amounts of a tarry, hydridic material.

Diborane, ethane and hydrogen chloride were identified and determined by condensing the fraction containing these on water.

Diborane and hydrogen chloride were measured by titration of the aqueous solution obtained. The material which did not react with water was measured as a gas and assumed to be ethane. Ethylpenta- 61 borane was identified by its vapor pressure, boron trichloride from its infrared spectrum, and ethyldichloroborane from the results of a hydrolysis of a sample into hydrogen chloride and ethylboric a c id .

A considerable amount of trouble was encountered in the fractionation of the products of this reaction due to dispropor-

tionation of the fractions during the fractionation process. This made the isolation of pure fractions practically impossible. The reaction, Reaction 79> is given in Table X.

Table X

Reaction of Pentaborane with Ethyl Chloride.

Charge Products

B5H9 4 8 .9 mmoles h2 25 mmbles

C2H5C1 55.0 mmoles C2H6 16.2 mmoles

AICI3 3.9 mmoles HC1 2 .1 mmoles

Time 48 hours B2Hfi 1 .2 mmoles

Temp. 25°C C2H5B5H8 25 mmoles

Vol. of Vessel 1000 cc BCI3 and C 2H5BCI2 were not measured.

6. Pentaborane and ethyl bromide.

Ethyl bromide was found to react with pentaborane in the

presence of aluminum chloride. A temperature of 90°1 was used for the reaction, but later work indicated that lower'temperatures could have been used. The products of the reaction included hydrogen, ethane, ethylpentaborane, ethyldibromoborane, and a large amount of tarry, hydridic materials. Other products were present, but were not identified.

Ethylpentaborane and ethyldibromoborane could not be separated since their vapor pressures were too close to permit any degree of separation. They were identified from the results of the oxidation and hydrolysis of the mixture. The data for the reaction are given in Table XI.

Table XI

Reaction of Pentaborane with Ethyl Bromide

Reaction 10 ______

B5H9 3 6 .7 mmole

C2H5Br 70.5 mmole

AICI3 1 .9 mmole

Temp. 90° C

Time 17 h rs .

Vessel size. 1000 cc.

Products

H2 50 mmole

G2H6 Wot measured

c 2h5b5h8 8 .0 mmole

C2H5BBr2 12.9 mmole m 7. Pentaborane and methylene iodide.

Pentaborane reacted very slow ly -with methylene io d id e. In this case, it was found that either aluminum chloride or boron trifluoride will serve as a catalyst. A temperature of 100°C and several days time was required for the reaction.

The products of the reaction included hydrogen, boron trichloride from the aluminum chloride catalyzed reactions, hydrogen iodide, methylpentaborane, a considerable amount of a dark, hydridic tarry material, and a crystalline product the identity of which is not certain. The yield of the latter was ex­ tremely small.

This crystalline material melted at about 60°C., and the results of analysis by oxidation and hydrolysis, given below, seemed to indicate that the material was diiododipentaborylmethane.

Theory fo r Analysis Found diiododipentaborylmethane

Boron (ox) 27.6 $ 27.8 $

Carbon (ox) 3.16 $ 3.08 $

Iodine(ox) 68.1 # 65 .0 $

Boron(hyd) 28.3 fo 27.8 #

Iodine(hyd) 63.6 % 65 .0 %

Mmoles H2 2.54 1° 2.51 $

C:B:I Cm .03^10.0^1.92 However, doubt is cast on this by a mass spectrographic analysis of the material which was kindly carried out by Dr. John Norman 2 0 of

20. John Norman, Olin-Mathieson Corporation, Niagara Falls, N.Y., Private Connaanication.

Olin-Mathieson. According to his interpretation of the mass

,0 spectra of a sample of the material, the sample consisted chiefly

of iodopentaborane and methyliodopentaborane. An equimolar mixture

of these would give approximately the same analysis as was obtained above.

Some typical reaction data are given in Table XII.

Table XII

Reactions of Pentaborane with Methylene Iodide.

Reaction 14 Reaction 15 Reaction 16

B5He 63. I mmole 52.1 mmole 50.1 mmole

CH2I 2 22.6 mmcle 18.0 mmole 1 6 .9 mmole

AICI3 2.8 mmole 3.4 mmole ---- 0 0 • BF3 ------4*72 mmole

Time 14 hrs. 67 h rs. 67 h rs .

Ten?). 105 °C 100°C 100°C

Vessel Size 1000 cc 1000 cc 1000 cc 65

Table XII (cont.)

Reaction 14 Reaction 15 Reaction 16

Products

BSHS 5 2 .1 mmoles 22.9 mmole 34*6 mmole

CH2I2 12.9 mmoles Not measured 5.3 mmole

b f3 ------4.56 mmole

h 2 13 mmole 41 mmole 23 mmole

HI (a) 0.8 mmole (a)

BC13 (a) 1.8 mmole

C.H3B5H3 (a) 2.4 (a)

Crystalline Material None 0.106 gram 0.145 gram

(a) The presence of this compound is not excluded by the data obtained, but the compound was not identified and measured.

8. Pentaborane and formaldehyde or paraformaldehyde.

Paraformaldehyde and pentaborane showed very little reaction even after seven days at 15Q°C. There was a slight amount of hydrogen and dimethyl ether formed in this time, but no boron containing compounds appeared to be present in sufficient quantities to identify. One reaction was tried in which para­ formaldehyde was first depolymerized to formaldehyde, but the only reaction in this case was the polymerization of the formaldehyde. C. Reactions of sec -But ylpent aborane.

sec-Butylpentaborane, obtained from a reaction of penta­ borane with 2-butene, was found to react with methyl chloride in the presence of aluminum chloride. The reaction went readily at room temperature. The products of the reaction included hydrogen, hydrogen chloride, diborane, methyldichloroborane, methyl-sec- butylpentaborane, and a considerable amount of a hydridic, tarry material. The reaction is given in Table XIII.

Table XIII

Reaction of sec-Butylpentaborane with Methyl Chloride

Reaction 87

C4HgB5Hg 36.7 mmole

CHCI3 92.7 mmole

AICI3 4.6 mmole

Temp. 25 °C

Time 16 hrs.

Vessel size 1000 cc

Products

H2 19 mmole

b2h 6 2.2 mmole

HC1 18.6 mmole

CH3BCI2 5.3 mmole

^ 5 ^ 12B5H7 13.4 mmole There was a considerable amount of disproportionation during the fractionation so some of the above figures may not be reliable.

Me thyl- sec -butylpentaborane was identified by oxidation. Analyses were carried out on two samples. Sample one was obtained from a fractionation train fractionation of the methyl-sec-butylpenta- borane. Sample two was taken from Fraction 2 of the distillation the met hyl-sec-but yip ent abo rane from a small s till under a low pressure of nitrogen. The following fractions were taken from this

distillation.

Fraction Boiling Range Pressure

1 78-81° C 50 mm

2 81 -83 °C 50 mm

3 82.5 to 84°C 50 mm

4 Variable 25 mm

The analyses gave the following results:

Theoretical for Sample 1 Sample 2 C5H12B5H7

Boron 39.0 % 40.1 % 40.6 £

Carbon 44.7 $ 42.1 $ 45.7 %

BtC B5.00O5.I8 B5i00C4#73

The results of the analyses indicate that the reaction

yielded methyl-sec-butylpentaborane. The carbon analysis for

sample 2 was low, but previous work has shown that the complete 68 oxidation of a long alkyl group is difficult, and a low figure for carbon is not unexpected.

Physical Properties of Methyl-sec-butylpentaborane.

Methyl-sec-butylpentaborane is a colorless liquid which freezes into a glass at low temperatures. The following physical measurements were made.

1. Infrared spectrum. The infrared spectrum of a liquid sample of methyl-sec-butylpentaborane is given in Eig. 18. The infrared spectra of sec-butylpentaborane is given in Fig. 19.

2. Vapor pressure. The vapor pressure of methyl-sec-butyl- pentaborane was determined over the range of 28-l50°C. There was a considerable amount of decomposition of the sample during the vapor pressure determination, and there was about 12 mm of gas which was not condensable at -196 present in the vapor pressure bulb at the end of the run. Two runs were made, but the amount of decomposition in the second run was as great as in the first.

It had been hoped that perhaps the dec 011530sition was due to a trace of moisture in the bulb or due to some impurity in the sample, and that the source of decomposition would be removed by the first run. It is possible, however, that the decomposition was caused by some trace impurity in the sample. We do not have enough information to be able to state that met hyl-sec -butyl- pentaborane is inherently unstable at elevated temperatures, since we did not know the purity of the sample and what the possible transmission 100 0 8 0 6 0 4 20 nrrd pcrm f ehls -butylpentaborane c Methyl-se of Spectrum Infrared ae egh microns length, Wave IUE 18 FIGURE J ______I______I______I______I______I______I------I------L ------1— L 6 8 10 12 14 Wave length, microns FIGURE 19

Infrared Spectrum of sec-Butylpentaborane 71 contaminants were. However, Ryschkewitsch has found that iso- butylpentaborane does decompose at 150oC ^ .

The vapor pressure data are given in Table XIV, and the plot of log p against l/T is given in Fig. 20. The vapor pressure is given by

- 2.14 X 103 . 7 rjr 1°S Pmm. ” y i *75 •

The heat of vaporization is 9>780 cal/mole, and the Trouton constant at the extrapolated boiling point of 164°C is 22.3 e. u.

3. Molecular weight. The molecular weight was determined to be 142. The theoretical value is 133.30* '72 ■

Table XIV

Vapor Pressure of Methyl-sec-butylpentaborane.

Temperature P ressu re °C °K 1/T x 103 mm Hg

28.4 301.6 3.315 3.9 35.2 308.4 3.242 6.7 39.9 313.1 3.193 8 .3 45.1 318.3 3.141 10.4 49.8 323.0 3.095 1 3 .2 55.1 328.3 3.045 17.5 60.0 333.2 3.001 21.6 66.6 339.8 2.942 28.9 71.0 322.2 2.905 34.8 75.2 348.4 2.870 42.1 80.7 353.9 2.825 50.9 85.0 358.2 2.791 6O.4 90.5 363.7 2.749 74.1 95.1 368.3 2.715 8 9 .3 99.7 372.9 2.681 1 05.2 104.5 377.7 2.647 124.1 108.6 381.8 2.619 142.9 112.0 385.2 2.592 160.7 115.1 388.3 2.575 178.1 118.0 391.2 2.556 196.2 120.3 393.5 2.541 211.2 122.5 395.7 2.527 225.3 125.8 399.0 2.506 248.1 130.0 403.2 2.480 275.0 132.2 405.4 2.466 297.5 134.2 407.4 2.454 319.6 137.3 410.5 2.436 350.9 140.0 413.2 2.420 379.4 142.2 415.4 2.407 405.3 144.1 417.3 2.396 429.9 145.3 418.5 2.389 447.7 147.0 420.2 2.379 4 6 8 .1 148.3 421.5 2.372 488.9 150.1 423.3 2.362 519.1 150.1 423.3 2.362 519.1 146.5 419.7 2.382 481.1 143.0 416.2 2.402 442.8 73 Table XIV (cont.)

Temperature P ressu re °C °K 1/T x 103 ram Hg

139.0 412.2 2.426 398.7 133.6 406.8 2.458 349.6 129.2 402.4 2.485 311.6 126.1 399.3 2.504 285.9 121.4 394.6 2.534 253.2 115.7 388.9 2.571 214.1 108.8 382.0 2.617 176.8 101.0 374.2 2.672 143.4 89.3 362.2 2.760 103.5 79.4 352.6 2.836 79.5 68.1 341.3 2.929 59.7 57.2 330.4 3.026 47.6 47.0 320.2 3.123 39.0 27.3 300.5 3.327 30.1 -78.5 22.4 - 196 . 11.4 Methyl-sec -butylpentaborane

FIGURE 20 D. Reactions of Pentaborane and Methylpentaborane vdth

H alides.

In the absence of a catalyst, neither pentaborane nor methylpentaborane react with hydrogen halides or alkyl halides.

However, in the presence of aluminum chloride as a catalyst,

reaction does take place, although some samples of aluminum chloride did not serve as a catalyst. All aluminum chloride used for this

work was resublimed, and the difference between the samples of

aluminum chloride was not known. Most of the reactions were rim

at 100°C for one day. The products of the reactions varied some­ what with the pentaborane and halide used, but a hydridic, non­

volatile material was always produced in addition to hydrogen and

boron trichloride or methyldichloroborane. The data for these

reactions are given in Tables XV - XVIII.

1. Pentaborane and hydrogen halides.

Tables XV and XVI

2. Methylpentaborane and hydrogen halides.

Table XVII

3. Methylpentaborane and methyl halides.

Table XVIII 76

Table XV

Reactions of Pentaborane with Hydrogen Chloride.

R eactio n 56 75 98 100 101

C haree

B5ffe 4. 52mmol 4.94mmol 5 . 14mmol 5. 03mmol 5.15ramol HC1 4«56mmol 4 . 94 ramol 4.83mmoi 4.80ramol 4 . 92 mmol AICI3 2 .0 mmol O.67mmol O.67mmol 0 . 74raniol O.73nnnol

Time 16 h r s . 24 h rs. 24 h rs . 24 h rs . 24 h rs . Temp. 100° C 100?C 100°C 100°C 100°C V essel s iz e 125 cc 125 cc 125 cc 125 cc 125 cc

P ro d u cts

h2 4 .7 mmol 6 .0 mmol None 4 .9 mmol 5.6 mmol BCI3 0.96mmol 1 .2 mmol None 1 .2 mmol 1 .1 mmol

Recovered Reactants

B5H9 3»40mmol 3.40mmol 5. 13mmol 3.22mmol 3.67mmol HC1 0 . 17mmol O.25mmol 4.85mmol 0 . 13mmol 0.13mmol

R eactan ts Consumed

b5h 9 1.12mmol 1.54mmol O.Olramol l.Slmmol 1.48mmol HC1 4.39mmol 4.69mmol 4 .67mmol 4«79mnol 77 Table XVI

Reactions of Pentaborane with Hydrogen Halides.

R eactio n 97 96 38 47

Charee

B5H9 5 .0 3 mmole 5.11 mmole 48.3 mmole 1 2 .3 mmole HBr 4 .7 1 mmole ------HI ------5 .2 0 -mmole 1 6 .2 mmole AICI3 0.80 mmole 0.7 6 mmole 3 .0 mmole 2.-6 mmole

Time 24 h rs. 24 h rs. 24 h rs . 24 h rs . Temp. 100° C 100"C 100°C 100° C Ve s s e l s iz e 125 cc 125 cc 1000 cc 125 cc

Products

h 2 None None 28 mmole 3 mmole BCI3 None None 2 .1 mmole ------HC1 None 0.44 —-

Recovered Reactants

BsHe 5.00 mmol 5.06 mmol 35.8 mmol 10.9 mmol HBr 4 .8 1 mmol — ------HI 4 . 7.5 mmol 0 .-36mmol

R eactan ts Consumed

B5H9 0 .0 3 mmol 0 .1 4 mmol 12.5 mmol 1 .4 mmol HX ----- 0 .5 5 mmol 1 5 .8 mmol ------Table XVII Reactions of Methylpentaborane with Hydrogen Halides.

R eaction 73 99 76 72 74

H alide HC1 HC1 HBr HI None

Charge

CH3B5H8 5. 30mmol 5 . 04mmol 5. 27mmol 5.18mmol 5 . 09 mmol HX 4.80mmol 4.94mraol 4.80mmol 4.80mmol None AICI3 O.76mmol 0 . 72mmol 0 . 68 mmol O.75mmol

Time 24 h rs. 24 h rs. 24 h rs . 24 h rs . 24 h rs. Ten?). 100° C 100° C 100°C. 100° C 100° C V essel Size 125 cc 125 cc 125 cc 125 cc 125 cc

Products

h2 5. 26mmol None 6 . 17mmol 5. 15ramol 0 . 60mmol CH3BCI2 1 .2 mmol None 0 .7 mmol 0.34 mmol None O thers (a) (b)

Recovered Reactants

B5H8 CH3 3.58nimol 4.93mmol 4 . 04mmol 3. 24mmol 4 . 87 mmol HX O.36mmol 5. 01mmol 0 .4 mmol

R eactants Consumed

CH3B5H8 1. 62mmol O.llmmol 1. 23mmol 1. 94 mmol 0 . 22mmol HX 4.44mmol 4 .S0mmol 4 * 40mmol

( a) 0.25 mmole of diborane was obtained from this re a c tio n .

(b) 0 .2 4 mmole of hydrogen chloride was obtained • -79 Table XVIII

Reactions of Methylpentaborane with Methyl Halides.

R eaction 69 71 70 68

H alide CH3G1 CH3CI CH3Br CH3I

Charge

CHsBgHg 4 .9 3 mmole 4 .7 1 mmole 5.13 mmole 4.95 mmole CH3X 4 .7 4 mmole 4 .5 9 mmole 4.77 mmole 4 .8 7 mmole AICI3 0.78 mmole O.6 9 mmole 0 .7 8 mmole 0.74 mmole

Time 96 h rs. 24 h rs . 24 h rs . 24 h rs . Temp. 25°C 100° C 100°C 100°C V essel S ize 125 cc 125 cc 125 cc 125 cc

Products

h2 0 .5 mmole 3 .7 mmole 4 .2 mmole 3.1 mmole CH3BCI2 1 .5 mmole 0 .9 mmole 0 .5 mmole O thers (a) (b) (c)

Recovered Reactants

ch3b5h8 4.72 mmole 2.89 mmole 3.24 mmole 3.20 mmole ch 3x 4 .5 9 mmole 1.25 mmole

R eactan ts Consumed

^ GH3B5H8 0 .2 1 mmole 1.82 mmole 1.89 mmole 1.79 mmole ch 3x 0.3 4 mmole 4 .5 9 mmole 4.77 mmole 3.62 mmole

(a) Methane was detected from this reaction. Approximately 0.4 mmole of hydrogen chloride was obtained.

(b) App. 1.0 mmole of a strong acid was obtained.

(c) App. 0.4 mmole of a strong acid was obtained. There was also a trace quantity of a product with a vapor pressure of 2 mm at 0°C, but there was not enough present for identification. V. Discussion and Conclusion

A. General

Alkyl derivatives of decaborane and pentaborane have been prepared by a Friedel-Crafts type of reaction. Pentaborane and alkyl halides, decaborane and alkyl iodides, and decaborane and ethylene in the presence of aluminum chloride as a catalyst yielded alkyl derivatives of the respective boron hydride.

The reactions of decaborane with alkyl iodides went very cleanly with little decomposition of the decaborane and with only traces of hydrogen being formed. Amounts of hydrogen iodide almost equal to the alkyl iodide which was consumed were produced by the reaction. A temperature of about 100°C was required for the reaction, with a time of several hours. An excess of the alkyl iodide was usually used, the larger the excess, the greater the ex­ tent of alkylation of the decaborane. Mono-, di-, and trialkyl derivatives of decaborane were formed by the reaction. No other halides were used, but it is reasonable to assume that bromides and chlorides would also have yielded alkyl decaborane.

However, the reactions of pentaborane with alkyl halides led to very extensive decomposition of the pentaborane or its derivative. The maximum yield of derivative was reduced to 50 to

60 per cent by this decomposition. Large quantities of hydrogen and non-volatile, hydridic, tarry residues resulted from this Sir decomposition. Diborane, boron trichloride, alkyldihaloboranes, and trialkylboranes v;ere other products which were obtained, but not a ll of these products were obtained from all reactions. Alkyl iodides required a temperature of about 100°C and several hours reaction time, but the reaction with alkyl bromides and chlorides went readily at room temperature in several hours. Only a mono- alkylpentaborane was found. There was no evidence for the formation of polyalkylpentaboranes. It should be noted that the reaction of s ec-butvlpentaborane. prepared from a reaction of pentaborane with

2-butene, with methyl chloride did lead to the formation of a methyl- s ec-butylpentaborane.

In a search for a clue to the cause of the extensive decompo­ sition which occurs in the Friedel-Crafts reactions of pentaborane, runs were made with various components of the reaction mixture.

Although hydrogen halides are an expected product of the Friedel-

Crafts reaction of alkyl halides, the amounts obtained from the pentaborane reactions were very small. To see if the hydrogen halides might not be reacting with pentaborane or the alkylpenta­ borane, reactions were run between the hydrogen halides and pentaborane or methylpentaborane. In the absence of aluminum chloride, no reaction took place. However, in the presence of aluminum chloride, reaction usually took place at 100°C. The reaction was not checked at lower temperatures. With one sample o f aluminum c h lo rid e , however, th e re was no re a c tio n . The reason m for this is not known since both samples were from the same source and were handled in a similar manner. Methylpentaborane was found to react with the methyl halides at 100°C in the presence of aluminum chloride. However, at room temperature only a slight amount of reaction took place between methyl chloride and methyl­ pentaborane in the presence of aluminum chloride.

Aluminum ch lo rid e was th e only c a ta ly s t which was ex ten siv ely used in this work. However, other Friedel-Crafts catalysts should be able to serve as catalysts for these reactions. Boron tri­ fluoride was tried, and served as a catalyst for the reaction of methylene iodide and pentaborane. It did not serve as a catalyst for reactions between ethyl iodide and pentaborane or decaborane.

Other halides were not checked, and no runs were made with other catalysts such as ferric chloride.

B. Structure

Nuclear magnetic resonance studies made on an alkylpenta- borane prepared by a Friedel-Crafts alkylation of pentaborane with an alkyl halide indicated that the alkyl group is attached to the apical boron of pentaborane^. Similar studies on isobutylpenta-

21. Shoolery, J., Varian Associates, Palo Alto, California, Private Communication. borane prepared by the reaction of pentaborane with isobutylene indicated that the alkyl group is attached to a base boron of the 0*1 tetragonal pyramid .

The chemical evidence obtained in this laboratory is in com­ plete agreement vdth this. The yields and conversions in the

Friedel-Crafts synthesis are high, yet no polyalkylpentaboranes were obtained from the reaction. Even when methylpentaborane was reacted with methyl iodide, there was no evidence for a poly- methylpentaborane. This is what would be expected if the Friedel-

Crafts synthesis were capable of yielding only an apically substi­ tuted pentaborane.

It should be pointed out that only monoalkylpentaboranes have been reported from the reactions of 1-butene^, 2-butene^, and

22. Altwicker, E. R., Ph. D. Thesis, The Ohio State University, Columbus, Ohio, To be published. isobutylene^ with pentaborane, where base substituted alkylpenta- boranes are formed. But in these reactions, in contrast to the

Eriedel-Crafts synthesis, the yields of alkylpentaboranes are low.

Thus the concentration of alkylpentaborane during the reaction is low, and any polyalkylpentaboranes would be formed in such small quantities that they would not have been isolated from the reaction mixture. The heavy fractions which would have contained any polyalkylpentaboranes which may have been formed were usually not worked up in these reactions. And no reactions were run between the monoalkylpentaboranes and an olefin*: Thus the arguments si presented for apical substitution for Friedel-Crafts derivatives do not hold for derivatives prepared from the olefin reaction.

A disubstituted pentaborane was prepared by reacting sec-butyl- pentaborane, obtained from a reaction between 2-butene and penta­ borane, with methyl chloride in the presence of aluminum chloride.

This is evidence for the formation of base substituted products by the olefin reaction. The sec-butylpentaborane formed by the reaction of 2-butene with pentaborane is substituted on the base and still has the apical position open for reaction with methyl c h lo rid e .

Note: According to recent rules on the nomenclature

of boron compounds, the apical boron is numbered one, the

base borons are numbered two, three, four and five, with

the lowest possible numbers being used. Char derivatives

are correctly names l-methylpentaborane-9,

l-ethylpentaborane-9, and 1-methyl-2-sec-butylpenta-

borane-9.

C. Theory of Reaction.

Quantum mechanical studies have been made on the electronic 1 ? structures of the hydroborons . An excellent review of this has been made by Ryschkewitsch who applied the results to the

alkylation of pentaborane with olefins^. The electronic structure

of pentaborane is discussed in terms of normal covalent, or two (

m center orbitals, and multicenter orbitals. Multicenter orbitals

are formed by the linear combination of single electron wave

functions from several atoms. This gives rise to one molecular

orbital for each single electron wave function used in the linear

combination. These molecular orbitals may be classified as

bonding, non-bonding, or anti-bonding according to their energies.

In the case of three center orbitals, linear combinations are made

of three single electron wave functions from three atoms. This

gives three molecular orbitals, one of which is bonding, one non­

bonding, and one anti-bonding.

Considering the structure of pentaborane, there are five

'normal* B-H bonds, using 10 of the 24 available electrons and one

single electron wave function from each boron. There are four

hydrogen bridges. These are constructed of three center orbitals,

each of which is formed from one atomic orbital from the hydrogen

and one from each boron at the end of the bridge. Each of the

four bonding molecular orbitals is filled with two electrons,

using 8 of the 14 remaining electrons with two orbitals from each

base boron being used to construct the bridges. This leaves six

electrons and seven orbitals (one from each base boron and three

from the apical boron) remaining to construct the bonds for the

boron framework. These seven atomic orbitals give seven molecular

orbitals. The energies of these are such that three of these may

be considered bonding, one non-bonding, and three anti-bonding. 86

The three bonding orbitals are filled with the six remaining e le c tro n s .

A consideration o f the coefficients of the atomic orbitals in the occupied molecular orbitals shows that each apical boron had a negative formal charge, with each base boron having a positive formal charge one-quarter that of the charge on the apical atom. A refined treatment gives the negative charge on the apical atom as -.32 to -.37* This charge is in agreement with the dipole moment of pentaborane^^. A consideration of the atomic

23. Hrostowski, Myers, and Pimental, J. Chem. Phys. , 20, 518 (1932). ______orbitals involved in the molecular orbitals shows that there are

5 /8 of an sp3 orbital unoccupied on each base boron, and 1/2 an sp, l/2 an px and 1/2 an py orbital unoccupied on the apical atom.

The structure of decaborane is treated similarly. This will not be discussed since the same considerations hold as for penta­ borane. The apical borons of the pentagonal pyramids are found to possess a negative charge.

These electronic considerations may be used in an explanation of the mechanism of the Friedel-Crafts alkylation of pentaborane and decaborane. According to current theory, the Friedel-Crafts reaction goes by an electrophilic attack of an aromatic nucleus by a positive species. The Friedel-Crafts catalyst (in this case m aluminum chloride) interacts with the alkyl halide to yield a species in which the alkyl group possesses positive polarity

+ f ' s RX + AICI3 ------**■ R — X AIGI3

Currently it is doubted that a free carbonium ion is actually formed. The R group, with positive polarity, induces a negative charge in the aromatic species, and the reaction proceeds by the formation of adduct between the aromatic species and the alkyl halide-Lewis acid adduct, which is followed by elimination of hydrogen.

The application of this mechanism to the Friedel-Crafts reactions of pentaborane and decaborane is simple. The reaction proceeds by an attack of the positive alkyl group on the negatively charged apical atoms of pentaborane and decaborane. As mentioned above, there are unoccupied orbitals on the atoms of pentaborane and decaborane. Upon the approach of the alkyl group toward the apical atom, the unoccupied orbitals may rearrange to form an orbital directed to provide maximum overlap with one from the approaching alkyl group, and an adduct may be formed between the pentaborane and the alkyl group,

B5!feR+ A1XV .

The decomposition of this adduct could take place in at least three ways*

1. Loss of hydrogen to yield an alkyl pentaborane and an hydrogen acid. m 2. Loss of the alkyl group to yield the reactants, unchanged.

3. Disruption of the pentaborane skeleton. This might account for some of the decomposition which occurs in the reaction, and w i l l be discussed more l a t e r .

Since trialkyl derivatives of decaborane are formed in the

Friedel-Crafts reactions of decaborane, attack^at points other than those of negative polarity must take place. It is possible that the alkyl group may induce a charge at some of the boron atoms in decaborane. To our knowledge, the structure of these alkyldeca- boranes has not been determined. r In addition to the alkyl derivatives of pentaborane, products of the reaction include diborane, boron trichloride, alkyl boron halides, trialkylboranes, as well as considerable quantities of hydridic, tarry materials. All of these products must involve a breakdown of the pentaborane skeleton, and their origin is not clear at this time. Only speculations may be made.

The roost likely mode of decomposition appears to be a break­ down of the pentaborane skeleton during the decomposition of the

B5I^R+ AIX4 adduct. I t was shown th a t the halogen acid s re a c t with pentaborane and with methylpentaborane, and that the methyl halides react with methylpentaborane in the presence of aluminum chloride, so these are possible sources of decomposition during the reaction. But since these reactions occur only in the presence of aluminum chloride, it seems likely that the reactions leading /

to decomposition of the pentaborane again occurs through the breakdown of a similar adduct. Exactly how this breakdown w ill occur cannot be stated. However, two possible modes of decompo­ s itio n may be v isu a liz e d .

1. There is evidence that BH3 groups may be obtained from the base borons in certain reactions. It is possible that BH3 groups may be released from the adduct quite readily. The BH3 groups so released may react with various components of the reaction mixture to yield some of the by-products. The remainder of the skeleton would give the tarry materials found in these reactions.

2. The apical boron atom may be freed from the remainder of the pentaborane molecule. The boron group formed may then i*eact with other components of the reaction mixture to yield some of the by­ products. It should be noted that a common product of these reactions was methyldichloroborane. This makes it seem likely that the apical boron was freed and the borane group picked up two atoms of chlorine from the aluminum chloride.

One other possible source of decomposition may be mentioned.

Strong Lewis bases react with pentaborane breaking up the penta­ borane skeleton. The AIX^ ion present in adducts is a strong

Lewis base, and may attack pentaborane or its derivatives during the reaction.

It should be noted that in the Friedel-Crafts reactions of

decaborane, there appears to be very little decomposition with only traces of hydrogen being formed. The halogen acid was formed

almost quantitatively. This may be interpreted in terms of deca­ borane being more stable than pentaborane. In the decomposition of the adduct, there is almost no tendency for the decaborane

skeleton to break down. Instead hydrogen is eliminated with the formation of hydrogen iodide. VI. Summary

Alkyl derivatives of pentaborane and decaborane have been pre­ pared by the reaction of alkyl halides with these hydroborons in

the presence of aluminum chloride. An ethyl derivative of decaborane

was prepared by the reaction of ethylene with decaborane in the

presence of aluminum chloride.

Methyl and ethyl derivatives of decaborane were prepared by the

reaction of decaborane with methyl and ethyl iodides, respectively.

These alkyldecaboranes were colorless liquids.

Methylpentaborane was prepared by the reaction of methyl

Ibromide, methyl chloride, or methyl iodide vdth pentaborane in the

presence of aluminum chloride. Methylpentaborane is a colorless

liquid boiling at 75.2°C, and melting at -55°C. The vapor pressure

from -31 to 75»5°C is given by:

lo 2 Pmm = * 1-°3 + 7.80. ' 1

Ethylpentaborane was prepared by the reaction of ethyl chloride,

ethyl bromide, or ethyl iodide with pentaborane in the presence of

aluminum chloride. Ethylpentaborane i s a c o lo rless liq u id melting

at -85°C, and boiling at 105.3°G. The vapor pressure from 0°C to

1Q6°C is given by:

l0S Pmm = -l-33,.x.lPl + 7.42 T

91 92

Methyl-sec-butylpentaborane has been prepared by the reaction of sec-butylpentaborane, prepared by the reaction of pentaborane with 2-butene, with methyl chloride in the presence of aluminum chloride. Methyl-sec-butylpentaborane is a colorless liquid which freezes into a glass at low temperatures and boils at 164°C. The vapor pressure from 23 to 143°C is given by:

log Pjjun = + 7. 75.

.Methylene iodide has been found to react with pentaborane with the formation of iodopentaborane and methyliodopentaborane.

Pentaborane has been found to react with the hydrogen halides in the presence of aluminum chloride. Methylpentaborane has also been found to react with the hydrogen halides and the methyl halides

in the presence of aluminum chloride. One sample of aluminum chloride did not catalyze these reactions.

The mechanism of the Friedel-Crafts alkylation of pentaborane

and decaborane has been discussed. BIBLIOGRAPHY

1. Altvd.cker, E. R., Ph. D. Thesis, The Ohio State University, Columbus, Ohio. To be published.

2. Dulmage and Lipscomb, Acta Cryst. . j>_, 260 (1952).

3. Eberhardt, Crawford and Lipscomb, J. Chern. Phys.. 22. 989 (1954). 4. Hrostowski, Myers and Pimental, J. Chem. Phys.. 20. 5 1 8 (1 9 5 2 ).

5. Hurd, D. T ., J . Am. Chem. Soc., 70. 2053 (194#).

6. Kasper, Lucht and Harker, Acta Cryst., J, 436 (1950).

7. Mezey, E. J., M. S. Thesis, The Ohio State University, Columbus, Ohio. 1954.

8. Norman, J., Olin Mathieson Corporation, Niagara Falls, New York. Private Communication.

9. Ryschkewitsch, G. E., Ph. D. Thesis, The Ohio State University, Columbus, Ohio. 1955*

10. Sanderson, R. T., Vacuum Manipulation o f Volatile Compounds., John Wiley and Sons, New York, 1 9 4 8 .

1 1 . Schaeffer, R., Abstracts of" Papers Presented at the Cincinnati Meeting of the American Chemical Society, April, 1955, P. 37Q. 12. Schaeffer, Shoolery, and Jones, Abstracts of Papers Presented at the Atlantic City Meeting of the American Chemical Society, 1956, p. 34 R.

13. Schlesinger and Burg, J. Am. Chem. Soc., 57, 621 (1950).

14. Schlesinger and Burg, Chem. Rev.. 31. 1 (1942).

15. Schlesinger, Florin and Burg, J. Am. Chem. Soc.. 61, 1078 (1939).

93 9«

16. Schlesinger, Horvitz and Burg, J . Am. Chem. S o c.. 58, 407 (1936). 17. Schiesinger and Walker, J . Am. Chem. Soc. . 57, 621 (1935). 18. Shoolery, J., Varian Associates, Palo Alto, California, Private Communication.

19. Stock, A., The Hydrides of Boron and Silicon, Cornell U n iv e rsity P ress, Ith a c a , New York, 1933* AUTOBIOGRAPHY

I , Samuel William Harris, was born in Chicago, I llin o is ,

January 27, 1930* I received my secondary school education in the public schools of Angola, Indiana, and my undergraduate training at Miami University, which granted me the Bachelor of

Arts degree in 1952. From Miami University, I also received the

Master of Science degree in 1953> sp ecia lizin g in the Department of Chemistry. In April of1953 > I entered the Graduate School of

The Ohio State University, where I specialized in the Department of Chemistry. While completing the requirements for the degree

Doctor of Philosophy, I held appointments as Research Assistant,

Research Fellow, and Research Associate with The Ohio State

University Research Foundation under the supervision of

Professor A. B. Garrett and Professor Harry H. Sisler.

95