EQUILIBRIA of ALUMINUM CHLORIDE with HYDROGEN CHLORIDE in AROMATIC HYDROCARBONS Dissertation Presented in Partial Fulfillment Of

EQUILIBRIA OF ALUMINUM CHLORIDE WITH HYDROGEN CHLORIDE IN AROMATIC HYDROCARBONS

Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By LEWIS DELMAR SWAN, B. A., M. Sc. The Ohio State University 1952

Approved by

vxser/’ TABLE OF CONTENTS Page I. Purpose...... 1 II. Historical...... 2 Part A. The HX-AIX,- Aromatic Solvent . 2 Part B. The Catalytic Species in the Friedel-Crafts Reaction.... 3 III. Preliminary Observations...... 16 A. Benzophenone-Aluminum chloride Complex...... 16 B. Effect of repeated sublimation of aluminum chloride ...... 17 C. Catalytic couple with mercury salts. 17- D. Effect of moisture...... 1 7 E. Preliminary studies with hydrogen chloride...... IS IV. The Specific Problem...... 3 0 V. Experimental...... 31 A. Apparatus...... 31 B. Purification and Preparation of Reagents...... 36 1. Aluminum chloride...... 36 2. Hydrogen chloride...... 38 3. Aromatic Hydrocarbons.... 42 a. b e n z e n e ...... 4 2 b. t o l u e n e ...... 43 c. mesitylene...... 45 4. Benzophenone...... 4 5 5. Miscellaneous: 02> HgO, N2 . . 46 C. Operational Procedures...... 47 D. Analytical Procedures...... 50 E. Summary of manipulatory difficulties encountered...... 52

VI. D a t a ...... 53 A. Benzene as Solvent...... 53 ii 809682 iii

TABLE OF CONTENTS (continued) Page

a. No complex without promoter. . . 53 b. Complex with promoter, ..... 56 c. Equilibrium constant...... 56 B. Toluene as Solvent...... 56 a. Toluene versus time...... 56 b. Complex with promoter...... 62 c. Equilibrium constant...... 62 C. Mesitylene as Solvent...... 67 a. No complex without promoter .. . 67 b. Complex...... 67 c. Equilibrium constant...... 67 d. Effect of oxygen ...... 72 VI. Discussion of Results...... 74 a. No Hydrogen chloride-aluminum chloride addition compound . . . 74 b. High aluminum chloride-benzophenone ratios ...... 74 c. Inorganic catalytic couples. . . 75 d. Repeated sublimation of aluminum chloride...... 75 e. Importance of promoters...... 76 f . Relative basicity of solvent . . 77 g. The role of water and oxygen . . 7S h. Ternary complexes...... 79 i. Evidence for hydrates...... 79 j. Evidence for dimer ...... SO k. "Red oil” complications...... SO 1. Distribution of aluminum chloride Si 91. Effect of oxygen on aluminum chloride-mesitylene system . . . S2 VII. Future Problems...... S3 VIII. Suranary...... S5 Autobiography. . , , LIST OF TABLES

No. I. Solubility of Aluminum Chloride in Benzene-Benzophenone Solutious at 20°C. (Molality xlo3) II. Effect of Repeated Sublimation on Solubility of Aluminum Chloride in Benzene at 20°C. III. Effect of Water on the Aluminum Chloride Benzophenone Ratio in Benzene at 20°C. IV. Effect of Aqueous Hydrogen Chloride on Aluminum Chloride Solubility in Benzene at 20°C. V. Effect of Hydrogen Chloride Atmosphere on Solubility of only Partially Pure Aluminum Chloride in Benzene at 20°C. VI. Promoting Effect of Water on Coordina tion of Aluminum Chloride with Hydrogen Chloride in Benzene at 20°C. VII. Co-ordination of Hydrogen Chloride with Aluminum Chloride in the Presence of Water in Benzene at 25°C. VIII. Effect of Water on the Solubility of Aluminum Chloride in Benzene with Subsequent Effects of Hydrogen Chloride and Water at 25°C. IX. Effect of Time on the Solubility of Aluminum Chloride in Toluene at 25°C. with Effect of Subsequent Water Addition. X. Co-ordination of Aluminum Chloride with Hydrogen Chloride in Toluene at 25°C. XI. The Solubility of Aluminum Chloride in Mesitylene Versus Time at 25°C. with Subsequent Air Admission, V

LIST OF TABLES (continued)

Page

XII. Solubility of Aluminum Chloride in Mesitylene at 25°C. as Affected by Hydrogen Chloride Addition and Subsequent Removal by Pumping. 70 XIII. Effect of Oxygen on Aluminum Chloride- Mesitylene System at 25°C. 73 LIST OF FIGURES Page 1. Effect of Benzophenone on Solubility of Aluminum Chloride in Benzene at 20°C. 20 2. Effect of Water on Aluminum Chloride- Benzophenone Ratio in Benzene at 20 C., 23 3. Effect of Aque;ous Hydrogen Chloride on the Solubility of Aluminum Chloride in Benzene at 20'G. o c 4. Preliminary Run.Effect of Atmosphere of Hydrogen Chloride on the Solubility of - Aluminum Chloride in Benzene at 20°C. 27 5. Equilibration Flask used in Aluminum Chloride-Benzophenone System. 2S

6 . Equilibration Vessel. 1/2 Scale 32

7. Sampling Flask. Full Scale 34 S. Manifold for Introduction of Hydrogen Chloride to System. 35 9. Aluminum Chloride Sublimation Manifold. 37 10. Block Diagram for Filling Hydrogen Chloride Addition Bulbs. 39 11. Hydrogen Chloride Addition Bath. 41 (Shown in Filling Position) 1-/2 Scale 12. Block Diagram for Purification and Addition of Solvent to System. 44 13. Benzene, Aluminum Chloride, Hydrogen Chloride, with Subsequent Water Addition.25 C .55 14. Benzene, Aluminum Chloride, Hydrogen Chloride Showing Effect of Water and Oxygen.2$°C. 56 15. Effect of Water on Solubility of Aluminum Chloride in Benzene.Subsequent Addition of Hydrogen Chloride and Water at 25°C. 60 16. Solubility of Aluminum Chloride in Benzene at 25°C. as Influented'.by the Presence of Water. 61 vi vii

LIST OF FIGURES (continued)

No. Page

17. Effect of Time on the Solubility of Aluminum Chloride in Toluene at 25°C. with Subsequent Water Addition. 64 IS. Solubility of Aluminum Chloride in Toluene at 25°C. as Influenced by Hydrogen Chloride. 66 19. Aluminum Chloride in Mesitylene Versus Time at 25°C. with Subsequent Air Admission. 69 20. Aluminum Chloride in Mesitylene at 25°C. with Added Hydrogen Chloride, Followed by Pumping. 71 ACKNOWLEDGMENT

Appreciation to Dr. Alfred B. Garrett for his suggestion of the problem and his guidance during the work is gratefully extended. Acknowledgment is also due the Office of Naval Research, United States Navy, and the du Pont Company for fellowships which enabled the completion of this work. The author also wishes to express his gratitude to his wife for her patience and understanding during the period of this study.

viii EQUILIBRIA OF ALUMINUM CHLORIDE WITH HYDROGEN CHLORIDE IN AROMATIC HYDROCARBONS

I. Purpose The purpose of this investigation was to study the equilibria of aluminum chloride with hydrogen chloride in aromatic hydrocarbons as solvents. This is part of a pro gram of elucidating the nature of Friedel-Crafts catalysis. Previously reported work has indicated that the true catalyst in those reactions ordinarily promoted by aluminum chloride might actually be tetrachloroaluminic acid formed in the equilibrium: AICI3 + HC1 HA1C14 . Although this substance has never been isolated and does not form in the absence of a solvent1, its salts of

1. H. C. Brown and H. W. Pearsall, J. Am.Chem.Soc., 73, 4631 (1951).

2 3 the form R+ AlCl^" are known (in the presence and absence of solvent).

2. E. Wertyporoch & T. Firla, Z.physik.chem., 162, 393-414 (1932).

3. Thomas, C. A., Anhydrous Aluminum Chloride in Organic Chemistry, Am. Chem. Soc. Monograph #37, New York, Reinhold Publishing Co., 1941, P 43-56. ------j------It was proposed: 1. To measure the solubility of aluminum chloride in aro matic solvents, specifically benzene, toluene, and mesit ylene, at 25° C.; 2. To measure the solubility of aluminum chloride in hydrogen chloride solutions of the same aromatic hydro carbons at several concentrations and at the same tempera ture; 3. To calculate equilibrium constants for the reaction indicated above if the reaction did not go to completion; and 4. To study the effect of moisture and oxygen on the equilibria involved. II. Historical

Part A. Data on the hydrogen chloride-aluminum chloride- aromatic solvent systems. Brown and Pearsall^ studied the

4. H. G. Brown and H. ¥. Pearsall, J.Am.Chem. Soc., 74, 191 (1952). ~

system hydrogen chloride-aluminum chloride-toluene at

-45.5° C. and -B0° C. Applying Henry’s law to their vapor pressure data they found co-ordination of hydrogen chloride and aluminum chloride in toluene. 5 Ipatieff and Komerewsky treated hydrogen chloride- 3

5. V. N. Ipatieff and V. I. Komerewsky, J.Am.Chem.Soc,, 56, 1926 (1934). saturated-benzene with aluminum chloride in a sealed bomb at 125° C. for twenty four hours and obtained about 1% biphenyl and ethylbenzene. The authors infer from these results that the catalyst induces destructive hydrogenation of benzene with formation of biphenyl and ethylenic frag ments. These ethylenic fragments then alkylate benzene under the influence of aluminum chloride to form ethyl benzene. They termed the process "destructive alkylation". Anschutz and Immersdorf^3, and Norris and Rubenstein^3,

6 . D. Nightingale, Chem. Rev. 2£, a.343, b.360 (1939). found that toluene, the xylenes, and mesitylene would similarly disproportionate to a small extent into higher and lower homologs under the influence of aluminum chloride. Part B. The catalytic species of the Friedel-Crafts reaction. Although the primary purpose of this investigation was not to elucidate the mechanism of Friedel-Crafts catalysis the results were such that they have a distinct bearing on. the catalytic species involved in such systems. A general dis cussion of aluminum chloride catalysis therefore follows. For years aluminum chloride has been used in the field of organic chemistry as a condensing agent to alkylate and acylate aromatic molecules, to polymerize unsaturat ed hydrocarbons, to crack and isomerize aliphatic and aromatic hydrocarbons and to effect the reaction of oxygen, sulfur, carbon dioxide, sulfur dioxide, and phosgene with aromatic hydrocarbons. It is also used to cause rearrange ments as in the Fries reaction. Such reactions have made its use a valuable tool in organic synthesis and in petroleum technology. 7 Friedel and Crafts were the first to report the use

7. C. Friedel and J. N. Crafts, Compt. rend., $4, 1392, 1450 (1377). of aluminum chloride to catalyze the condensation of alkyl and aryl halides with various aromatic compounds to sub stitute an alkyl or aryl group for one or more hydrogen atoms of the aromatic molecule. During the years since their original work, it has been discovered that a number of other catalysts such as AlRr-j, BF-j, SbCl^, ZnCl2 , FeCl^, TiGl^, HF, H2SO4 , H-jPO^, and P^O^q will also effect alkyl substitution of aromatic compounds by a variety of molecules including alkyl halides, olefins, alcohols, highly strained cyclo- paraffins, and esters. A measure of the relative catalytic activity of various Lewis acids was obtained by Dermer, Wilson, Johnson, $ and Dermer for the condensation of toluene with acetyl

S. 0. Dermer, et als., J. Am. Chem. Soc., 6^, 2SB1 (1941). chloride to give para methyl acetophenone. For this con densation they found the following order of effectiveness of the catalysts used: AlCl^ } SbCl^ > FeCl^ y TeCl2 ^ SnCl4 > TiCl4 > TeCl4 > BiCl3 > ZnCl2 . Simons, who has studied the use of hydrogen fluoride as a condensing agent for alkylations of the Friedel-Crafts type, reported the use of hydrogen chloride as an alkylation catalyst for the relatively simple case of para tertiary butyl toluene from toluene and tertiary butyl- chloride^.

9. J. H. Simons and H. Hart, J. Am. Chem. Soc., 66, . 1309-12 (1944).

Although hydrogen chloride alone is in general in- 10 effective as a catalyst for alkylation it has been dem-

10. Price, C. C., Organic Reactions, Vol. Ill, New lork, John Wiley and Sons, 1947, p 3. onstrated that the alkylation of aromatic molecules by olefins with aluminum chloride as the catalyst is aided by the acidic "assistant" of anhydrous hydrogen chloride^. 6

11. T. M. Berry and E. E. Reid, J. Am. Chem. Soc., 49, 3142 (1927).

This work might imply that the true catalyst for Friedel-Crafts reactions is the addition compound, HAICI^. Thomas3 gives several references to the increased catalytic effect induced by the addition of hydrogen chloride in alkylation and cracking reactions. Since aluminum chloride is known to form addition compounds with ammonia, hydrogen sulfide, hydrogen cyanide, and phosphine he proposes the compound HAICI4 as the analogous addition compound formed with hydrogen chloride. :C1: .. :C1: .. :6i: H:C1: + Ai:Cl: ^ H:C1: Al:Cl: ^ H+ + :C1:Ai:Ci:“

:C1:"• . " :C1:" «• • ■ " :Ci: » • ” Although tetrachloroaluminic acid has not been isolated, its salts of the form R+A1C1^~ are claimed to exist^ and may partially explain the nature of the nred oil” encountered in reactions employing aluminum chloride. Brown and Pearsall based their conclusions on Henry’s law data which indicated that aluminum chloride and hydrogen chloride formed a 1-1 ratio complex in toluene at -B0° C. and a 2-1 ratio complex at -45.5° C. corresponding to ArH+ AlCl/j" and ArH+ AI2CI7” . Since it is known that the red oils are much better solvents for aluminum chloride than the hydrocarbons themselves, these polyacids, similar to 7 those formed on the addition of sulfur trioxide to sulfuric acid, may well be the composition of the dark, oily "red oil" The carbonium ions of Whitmore explain the formation of isopropyl benzene from benzene and n-propyl chloride as well as with isopropyl chloride under the influence of alum inum chloride without the intermediate formation of an

12. F. C. Whitmore, J. Am. Chem. Soc., 3274 (1932).

13. C. C. Price, Chem. Rev., 29, 37 (1941).

H3C-CH2-CH2C1 + AICI3 ^ H3C-CH3-CH2+ AlCl^"

H3C-CHC1-CH3 + AICI3 A1C14” + (GH3 ) C+H

H+ + AICI4" ^ AICI3 + HC1

Friedel and Crafts once felt that the course of the alkylation proceeded through the agency of an intermediate by the following pattern^.

14. C. Friedel and J. M. Crhfts, Compt. rend., 100, 692 (1805) d C6H6 + AICI3 ^ C6H5 .A1C12 + HC1 . C6H5 .A1C12 + RC1 C^HjR + AICI3 . However, it was later learned that organoaluminum compounds of this type are not formed under the experimen tal conditions for alkylation and that compounds like

G5H3AICI2 do not yield hydrocarbons readily when added to alkyl halides. ' Prins^ and later Dougherty‘S pictured the mechan ON ON 1—1 C\J c*-

15. H. J. Prins, Chem. Weekblad, 24, 615 •

16. G. Dougherty, J. Am. Chem. Soc., 51, 576 (1929). ism as an interchange of ions, an alkyl carbonium ion and an aryl carbamion. RC1 + AICI3 ^ RAlCl^i^r R+ (AlCl^) “

C6H6 + AICI3 iS'C^AlClj ^ (C^AlCLj)" H+ followed by

(C5H3AICI3 )" H+ + r+ (aici4“) (c6h5aici3 )" R+ + h+(aici4 )“ C6H5R + AICI3 HC1 + AICI3 The mechanism,reviewed by Price, is most widely accepted at the present time; it too proceeds by means of a transient carbonium ion^.

17. C. C. Price, Chem. Rev., 29, 45 (1941). RC1 + AlCl^ ^ R^AICI^"*. The alkyl or aryl carbonium ion then introduces a strain the aromatic molecule and attacks at a seat of high electron density with the expulsion of a proton.

H+ + A1C14“ HC1 + AICI3

This parallels the mechanism accepted for the migra tion or removal of a bromine atom from an aromatic hydro carbon by halogen carrier. Data which support the Price viewpoint are those of Klit and Langseth^, Fairbrother"^, Bodendorf and Bohme^, 21 22 Wertyporoch , and Korshak and Kolesnikov l£. A. Klit and A. Langseth, Z. phyzk, chem., A176,65 (1936).

19. F. Fairbrother, J. Chem., Soc., 1937* 503.

20. K. Bodendorf and H. Bohme, Ann., 516, 1 (1935).

21. D. Nightingale, loc.cit., 329, 362-5.

22. V. 7. Korshak and G. S. Kolesnikov, C. A., 40 4033 (1946).

Klit and Langseth deuterated benzene in good yield with deuterium chloride using aluminum chloride as catalyst. Their proposed mechanism is similar to that of Price. 10 : Cl: .. : Cl: .. D:C1: + Ai:Cl: ^ D+ + :Cl:Al:Cl: :Cl: *’ :C*1: '* • •

Fairbrother found that radioactive aluminum chlor ide mixed with tertiary butyl chloride in benzene undergoes a complete interchange of chlorine atoms, the chlorine which formed hydrogen chloride having an activity equal to that of the chlorine combined in the final reaction mixture. This would indicate as the first step the ionization of a covalent G-Cl bond by means of AlCl^ in the formation of R+ (A1C14 )“. Bodendorf and Bohme obtained confirmatory evidence for the R?MX4” ions from a study of the racemization of phenylmethylchloromethane. The optical activity of this compound was found to disappear through complex coordination in accordance with the equation:

0 -j£ - Cl + MCI., (0 - + (m c i 4 )“ ch3 >

The strong increase in the specific conductivity of ethyl chloride, cylcochlorohexane, the propyl chlorides, benzoyl and acetyl chlorides induced by the addition of aluminum chloride led Wertyporoch to the assumption that complexes of the R+A1C1^“ type were formed. He thought these salt-like complexes to be relatively unstable, but that with an aromatic molecule they could form ternary 11

complexes (addition compounds of uncertain composition) wherein alkylation took place. Conductance and trans ference studies prompted the proposed formula [A1 (C2Hbromide, ethyl bromide, and hexaethylbenzene. Korshak and Kolesnikov studied the condensation of benzyl halide with benzene using aluminum halides as the condensing agents. On the basis of the formation of the J f ion (XAIX3 )- the expected values for HX and HX in the off gas would be 25$ and 75$. Their data support the forma tion of such an ion as an intermediate in the alkylation.

* 25.67$ HC1 CaHcCHoCI + AlBro + CaH6 ^ 5 2 3 6 6 N . 7 4 . 335& HBr 79.41$ HC1 C^HeCHoBr + AlClq + CaHa 6 5 2 3 20.59$ HBr Burbage’s thermal studies on the aluminum bromide-

organic compound systems definitely show 1-1 addition compounds formed between ethyl bromide and aluminum bromide and benzophenone and aluminum bromide 23 .

23. J. J. Burbage, Ph. D. dissertation, The Ohio State University, (1947).

The Russians, Korshak and Lebedev^, explained the

24. V. V. Korshak and N. N, Lebedev, C. A., 43, 2930d (1949) C. A., 44, 69351, (1950). 12 existence of aluminum chloride in the dimeric state as due to resonance between the forms

X\ * -^X Xv _/X + X N A1* X A1. N A1^ / / \ — / \ \ X X X. X X X. I II They believed the presence of the powerful dipole Hr _ AICI2 AlCl^ which induces a strong polarization in organic molecules to be the key to the catalytic activity of aluminum chloride. They cite the existence of •m [A1C1 *nRx] [AlCl^] as evidence. The following is their mechanism for the aluminum chloride induced alkylation of an aromatic molecule by alkyl chlorides:

C12A1+ Clf9-- E® Cl, Al” # --- -Ar® and 4 Cl^Al" C12A1+

show the polarity induced in the alkyl halide and aromatic hydrocarbon. Then, C12A1+ Cle iP C12A1+ ci^-..iP : ! ^ \ J Al2Cl6+ArR+HCl. C14A1" H® Are CI4AI" H ^ - A i ®

They thus picture the role of the catalyst as that of a strong polarization agent within a ternary complex. This polarization effect does not seem likely from the point of view that resonance between their structures I and II would be neither structure alone and hence the 13

dipole would not be stable or exist. However, a dissocia

tion into AlC.l2+ and A1C1^“ rather than the resonance might validate their mechanism. Finally, mention should be made of the opinions of several investigators who found that aluminum chloride alone or even the catalyst couple, aluminum chloride-hydrogen chloride, to be inadequate for isomerization and polymeriza tion unless traces of moisture, oxygen, or other proton acceptors were present. (References 25-29). 25 Lien ' and others point out that, although hydrogen

25. A. Lien, d ’Ouville, Evering, Grubb, I. and E. Chem., 44, 351 (1952).

chloride acts as a promoter for aluminum chloride in commercial isomerizations of alkanes, the conditions are such that intrusion of air or traces of moisture are poss ible and they account for the increased activity on the basis of these proton acceptors. 2(5 Pines and Wackher in a series of articles found

26. H. Pines and R. C. Wackher, J. Am. Chem. Soc., 6S, a. 595, b. 599, c. 1642, d. 2516 (1946). that traces of olefins, water, and oxygen as air would promote the catalytic activity of aluminum halides in isomerization. 27 Ipatieff and Schmerling also found this to be the 14

27. V. N. Ipatieff and L. Schmerling. I. and E. Chem., 40 , 2354 (1943). case and also implied that increased solubilization of aluminum chloride in the aromatic hydrocarbon in homogeneous phase alkylation with alkyl halides or olefins could account for the catalytic activity. He also found nitromethane 2$ effective as a solubilizing agent for aluminum chloride

28. L. Schmerling, I. and E. Chem., 40, 2072 (1943).

29 Stevenson and Beeck maintained that hydrogen

29. D. P. Stevenson and 0. Beeck, J, Am. Chem. Soc., 70, 2 8 9 0 (1948). ~ chloride alone is no promoter for the aluminum chloride catalysed isomerization of hydrocarbons, but that the presence of small amounts of water had a promoting effect. They found the composition of the catalyst to be

AI2CI5 ^(0H)q 5 and assumed this must be a mixture of AI2CI5 with A^Cl^OH or AlCl^ and HOAICI2 . They believed a whole series of catalysts of the formula Al2X^_n (0H)n , (l4n-5), to be possible, Numerous reviews on the use of aluminum chloride as a catalytic agent are available. In addition to Thomas’ 13 21 "sq book, the reviews by Price , Nightingale , and Calloway-' 15

30. N. 0. Calloway, Chem. Rev., 1£, 327 (1935). should be mentioned. The annual nChemical Engineering Unit 31 Processes Review” of Industrial and Engineering Chemistry

31. P. H. Groggins, I. and E. Chem., 42, l60& (194$). ibid. 41, 1S£0 (1949). ibid. 42, 1690 (1950). ibid. 43, 1 9 7 0 TT951). ~ contains a section on Friedel-Crafts reactions. 16

III. Preliminary Observations

In the course of a recent, unpublished investiga tion on the system benzene, benzophenone, aluminum chloride

the present investigator made several observations that prompted the present study. The complex formed between aluminum chloride and 32 benzophenone is well known. It is assumed to be formed

32. C. A. Thomas, loc.cit., p 50. by the aluminum atom of aluminum chloride completing its octet in accepting an elect iron pair from the carbonyl oxygen atom of benzophenone. :C1: Cl: .. 0:C: :0: + A1:C1: 0:C: :0 A1' ' :C1:e - 0 :Cl: 0 Cl:

A) It was proposed to measure the equilibrium constant for the reaction above by determining the solubility of aluminum chloride in benzene followed by solubility deter minations of aluminum chloride in solutions formed by the addition of known amounts of benzophenone.

From the slope of the curve in a plot of the form:

conc. A1C1 mol. conc~02^O 17 the ratio of aluminum chloride to benzophenone could be obtained. At equilibrium,

02CO + AICI3 (s) ^ j^COAlCl^, where x is mole ratio (1-x) (1 ) (x) of complexed aluminum chloride to total benzophenone, if = x 1-x

But x for all cases studied was greater than one, and the greater the initial solubility of aluminum chloride in benzene the greater the aluminum chloride-benzophenone ratio. This was attributed to the presence of water, air, hydrogen chloride, or other contaminants. (Table I, Figure 1). B.) It was found that repeated sublimations of aluminum chloride in an inert nitrogen atmosphere reduced the sol ubility of the product in benzene. (Table II). C) The sampling device and stirring mechanism had been protected by mercury seals. At one time it was thought that pressure fluctuations and agitation might entrain mercury or mercury salts. Studies of contamination of the system with these reagents produced highly colored mixtures and may have accounted for irreproducibility encountered in the study of the three phase system. ]>.) Since moisture could have such a debilitating in fluence on the study as it was proposed, the effect of small concentrations of water was studied. The result of 18 small water additions increased the solubility of aluminum chloride in benzene. Although the effect is not great it appears that the greater the aluminum chloride concentra tion resulting fuom water addition, the greater the re sultant aluminum chloride-benzophenone ratio when benzophenone is added, (Table III, Figure 2). The addition of moisture to aluminum chloride could release hydrogen chloride. It was thought that this too might complex with aluminum chloride and thereby increase the solubility of the metal halide in the hydrocarbon. Hydrogen chloride in the presence of a known amount of moisture was found to increase the solubility of aluminum chloride in benzene. (Table IV, Figure 3). £.) In another experiment a partial pressure of hydro gen chloride was maintained over a slurry of only partially pure aluminum chloride (see note 2, below) and benzene. The solubility of aluminum chloride in the system was greatly increased. (Table V, Figure 4). A preliminary study of the binary system hydrogen chloride, aluminum chloride at 40° C. and at 10° G. showed no evidence for compound formation by vapor pressure data. Experimental notes: (1) The equilibration flask used in . 4 this work is shown in Figure 5. Benzene was distilled in through the 5/12 spherical joint under an inert nitrogen atmosphere. 19

TABLE I Solubility of Aluminum Chloride in Benzene-Benzophenone Solutious at 20°C. (Molality x 10-'). AlCl^ (C6H5 )2 CO Legend Slope=AlCl2/C6H5 )2CO

1.84 0.0 1.76 0.0 29.2 24.2 29.2 24.2 1.14 58.2 49.4 62.9 49.4 2.6 0.0 2.7 0.0 5.8 3.0 5.9 3.0 0 1.36 8.4 3.8 8.4 3.8 18.5 11.3 17.7 11.3 2.8 0.0 3.0 0.0 71.2 50.0 73.7 50.0 70.8 50.0 © 1.36 77.9 59.1 82.2 59.1 83.2 59.1 87.5 61.7 86.9 61.7 87.6 61.7

2.5 0.0 3.1 0.0 35.5 24.1 40.3 24.1 40.6 24.1 56.8 39.3 1.57 64.5 39.3 63.9 39.3 78.5 46.4 78.8 46.4 81.0 46.4 ro MOLALITY ALUMINUM CHLORIDE x 10 90 80 20 30 70 50 40 60 — 100 OAIY EZPEOE I 3 BENZOPHENONE I0 x MOLALITY 20 20 FET F EZPEOE ON BENZOPHENONE OF EFFECT OUIIY FAUIU CHLORIC ALUMINUM OF SOLUBILITY N EZN A 20°C. AT BENZENE IN 30 ( U4) (U 1.57 050 40 (1.36) IUE 1 FIGURE 0 6

TABLE II

Effect of Repeated Sublimation on Solubility of Aluminum Chloride in Benzene at 20°C.

Molality AlCl^xlO^ Ave. *

Anhydrous, from bottle 19.5, 19.1, 19.5 19.4 0.17 First Sublimation 5.9, 7.7, 3.6 7.4 0.43 Second Sublimation 6.4, 6.4 6.4 0.50 Third Sublimation 3.5, 3.3, 2.3 3.2 1.00

♦Effectiveness of treatment based on third Sublimation Solubility. 22

TABLE III

Effect of Water on the Aluminum Chloride-Benzophenone Ratio in Benzene at 20° C. (Molality x 10^) aici3 h2o (0^ 5)2 CO Legend Slope

1.5 0.0 0.0 2.1 0.0 0.0 1.9 0.0 0.95 mAlGl3/mH20 3.6 1.9 0.0 4.0 1.9 0.0 3.3 1.9 0.0 10.1 3.3 x 9.3 3.3 9.9 3.3 1.74 mAlCl3/m(C^H^^CO 9.5 3.3 31.5 15.6 30.8 15.6 1.7 0.0 0.0 1.9 0.0 0.0 1.7 0.0 0.0 4.1 2.5 0.0 4.4 2.5 0.0 0.95 mAlCl3/mH20 4.0 2.5 0.0 6.2 4.6 0.0 5.3 4.6 0.0 6.4 4.6 0.0 12.0 2.6 e 11.5 2.6 11.0 2.6 1.92 mAlCl3/ m ( )2C0 11.0 2.6 15.4 4.9 15.2 4.9 15.6 5.0 16.0 5.0 16.6 5.0 16.1 5.0 ro o MOLALITY AICI x 30 28 24 26 20 22 0 OAIY AE ADO BENZOPHENONEx103 AND/OR WATER MOLALITY \0.95) 4 8 FET F AE O ALUMINUM ON WATER OF EFFECT HOIE EZPEOE RATIO BENZOPHENONE - CHLORIDE N EZN A 20°C. AT BENZENE IN 23 (1.92) IUE 2 FIGURE 12 (174) 16 X

TABLE IV

Effect of Aqueous Hydrogen Chloride on Aluminum Chloride Solubility in Benzene at 20°C.

Molality AlClo Time from Treatment, at ( ) , * 1st xlO^ Sample System became -

2.3 0, hours 2.3 0,hours 2.6 30,hours 2.6 30,hours 3.1 101,hour s 3.4 101,hours 0.0009 molal in H2O (A) 0.0003 molal in HC1 4.2 123,hours 4.4 123,hours 4.2 171, hours 4.3 171,hours 4.6 199,hours 4.7 199,hours 0.023 molal in H2O (B) 0.007 molal in HC1 6.1 290,hours 6.1 290,hours 9.5 34 3 ,hours 9.1 343,hours 9.7 355,hours 9.9 355,hours (C) 0.0004 molal in (C^H^^CO

9.5 402,hours 9.6 402,hours 9.9 492,hours 9.a 492,hours MOLALITY AICI 10 0 ______

I ______100 I __ 0 0 2 TIME J I ! _J N HOURS IN N H SLBLT O AUIU CHLORIDE ALUMINUM OF SOLUBILITY THE ON FET F QEU HDOE CHLORIDE HYDROGEN AQUEOUS OF EFFECT N EZN A 20°C. AT BENZENE IN 00 400 0 30 ______I ______FIGURE I ___ 3 _J 500 _

TABLE V (see Figure 4) Effect of Hydrogen Chloride Atmosphere on Solubility of only partially pure Aluminum Chloride in Benzene at 20°C.

Molality AlCl^xlO^ Time, Days

2.5 2.4 0 3.1

3.1 3.0 1 3.1 3.5 3.6 5 3.5 40.0 40.6 7 33.6 51.3 52.5 52.3 39.0 90.3 23

HC1 admitted after 5th day. MOLALITY AICI .03 .02 .08 .U{ .04 .05 .10 09 0 4 8 IE N DAYS IN TIME . 27 12 RLMNR RUN PRELIMINARY OUIIY F ALUMINUM OF SOLUBILITY OF ATMOSPHERE OF EFFECT YRGN HOIE N THE ON CHLORIDE HYDROGEN HOIE N EZN AT 20°C. BENZENE IN CHLORIDE 16 FIGURE 0 2

s e

£qo 2 %

(2) Aluminum chloride was doubly sublimed under a dry nitrogen atmosphere into small bulbs that clamped on the 18/9 spherical joint, but this transfer was made in the open air. (3^ Samples were withdrawn into 25 ml. glass stopp ered volumetric flasks through the side arm under a pressure of dry nitrogen. (4) A magnetic stirrer permitted agitation. The whole assembly was immersed in a constant temperature bath. 30

IV The Specific Problem.

The preliminary work with aluminum chloride, benzene, and hydrogen chloride indicated that a more comprehensive study of the system would be desirable. The solubilizing effect of the hydrogen chloride implied complex formation of the type indicated by

:C1: :C1: > i •• • • , H :Cl: + :A1: Cl*. H :C1: A1 :C1: ” •• .. :Cl: :Cl: » • . •

It was proposed to try to measure the equilibrium constant for the formation of tetrachloroaluminic acid in aromatic solvents at room temperature. The solubility of aluminum chloride in benzene, toluene, and mesitylene at 25°C. was determined and the solubility of aluminum chloride in benzophenone solutions of the same aromatic hydrocarbons was also obtained. It was also found to be necessary to obtain the effect of water (and oxygen) on the solubility of aluminum chloride in the aromatic hydrocarbons to explain some of the data already obtained. 31

V . Expe riment al

A. Apparatus. The apparatus for this research (Figures 6,7>8) consisted of an equilibration flask, (Figure 6), connected to a manifold, (Figure S), to which were attach ed bulbs containing hydrogen chloride. This manifold was joined to a mercury manometer and a pumping system. Both the equilibration flask and the manifold were immersed in constant temperature baths. Auxiliary equipment was used for the preparation, storage, and introduction of reagents. The sampling bulbs shown in Figure 7 were also employed. The equilibration flask, (Figure 6), is of about 300 ml. capacity. Two larger flasks of 650 ml. and £75 ml. were also used in this study. Agitation was obtained by using a glass sealed Alnico magnet in the flask. No difficulty was encountered in stirring the slurry even though the driving magnet was several centimeters below the flask and acting through several thicknesses of glass and water. The tubes attached at the top of the flask are for addition of aluminum chloride and aromatic solvent, con nection to the hydrogen chloride manifold, and for a sampling device fitted at the lower end with a sintered

glass filter tip. Samples were collected in the sampling bulbs 3 2

to benzene addition bulb Double strength wall K> aluminum chloride 'sublimation manifold

Dog ears" for spring c la m p s

# 7 3 4 7 stopcocks ■==7 //

2 0 $ joint to sampling flask 12 x 3 5 £ joint to hydrogen chloride manifold

Porous filter tip Magnetic stirring bar

FIGURE 6 EQUILIBRATION VESSEL

/ 2 Scale 33

delineated in Figure 7. The sampling method will be discuss ed later. The water baths containing the equilibration flask and the hydrogen chloride manifold were set at 2#°C. Close temperature control was maintained by means of a mercury thermoregulator, a Thyratron circuit of conventional design, a 200 watt heater, and a centrifugal pump circulating cold water from a cold reservior. The temperature was maintained constant to well within a tenth of a degree. The hydrogen chloride manifold is depicted in Figure S. The standard taper joints connected the manifold to the equilibration flask and to the monometer and vacuum system. Tight, leak free joints were maintained by springs connect ing the "dog ears” on the respective members. An open end, U shaped mercury manometer was included within the system and pressure readings were used to deter mine equilibrium conditions. 34

To equilibration flask

Jg !ljs Joint

Micro stopcocks

To vacuum line

FIG U R E T SAMPLING FLASK

Full scale Dog ears" for spring clamps 35 ^ Joint to manometer and vacuum line _____

35 $ Joint to equilibration flask

Water bath

Glass enclosed magnet for breaking tap

Hydrogen chloride addition bulb —

FIGURE 6 MANIFOLD FOR INTRODUCTION OF HYDROGEN CHLORIDE TO SYSTEM

~ % Scale 36

B. Purification and Preparation of Reagents. 1. Aluminum Chloride. The aluminum chloride used in this research was Baker and Adamson, C. P., anhydrous alum inum chloride. It was refined by a three-fold vacuum subli mation using the apparatus shown in Figure 9. The standard taper fitted tube, A, was filled approximately 2/3 full with aluminum chloride from the stock bottle and sealed with a standard taper cap| the above operations were performed in a dry box. The dry box was monitored with open Petri dishes containing phosphoric anhydride and continually flushed with dry, oxygen-free nitrogen. Between additions the stock bottle of aluminum chloride was kept in a vacuum desiccator charged with phosphoric anhydride. After filling, the addition tube was fitted to the oven-dried sublimation manifold. The stopcock to the vacuum line was then opened and the apparatus, including the equilibration flask, was flame brushed during the evacuation for several minutes to dispel occluded moisture, but the addition tube itself was brushed only lightly. The stopcock was then closed and the glass finger on the extreme right was immersed in liquid air. A small portion of the aluminum chloride was then sublimed into this tube by gently heating the addition tube with a hand torch. This portion was discarded. To Vacuum Line

Double Strength Wall "

To equilibration flask. Flame sealed after addition

F IG U R E 9

ALUMINUM CHLORIDE SUBLIMATION MANIFOLD ~ Sea I e 33

The glass finger to the left of the addition tube was then immersed in liquid air and the remainder of the reagent was slowly sublimed into it by gently heating as above. This procedure was repeated in subliming the powder into the next finger. The equilibration flask was then cooled with liquid nitrogen and a third sublimation drove the aluminum chloride into it. After this third sublimation the equilibration flask was sealed off at the heavy wailed juncture to the sublima tion manifold with a hand torch. 2. Hydrogen Chloride. Matheson, anhydrous, 99.9% purity, hydrogen chloride was prepared for use in this research as indicated in the block diagram, Figure 10. All the stopcocks except No. 3 were opened and the system was brush flame heated during evacuation. After cooling under vacuum the metering bulb was immersed in the water bath. The hydrogen chloride addition bulb was then placed in a liquid nitrogen bath as shown in Figure 10. Stopcocks Nos. 2 and 5 were now closed. Hydrogen chloride was admitted from the tank through a dry ice-acetone trap and layers of phosphoric anhydride until the manometer indicated slightly more than one atmosphere of gas in the system. Stopcock No. 1 was then closed. Hydrogen chloride was then bled off by manipulating stopcock No. 3 until one atmosphere of pressure was indicated on the manometer. Stop- Duo Sea I

Liquid Air Phosphoric Anhydride Column

Hydrogen Dry Ice Phosphoric Chloride - & - s Acetone Anhydride -o- Tank Column

Manometer

FIG U R E 1 0 BLOCK DIAGRAM FOR FILLING HYDROGEN CHLORIDE ADDITION BULBS

a Represents a tygon connection 44) cock No. 4 was then closed and No. 5 subsequently opened; the hydrogen chloride distilled into and froze in the liquid nitrogen-cooled bath. The barometric pressure was then read, and after two minutes the hydrogen chloride addition bulb was sealed off as indicated in Figure 11. A dozen or more of these bulbs were filled at a time. The first one filled was discarded before sealing. The volume of the metering bulb was known, 163.6 ml., the tem perature and pressure also known; hence Berthelot’s equation could be used to compute the weight of hydrogen chloride in each bulb. That the transfer from the metering bulb to the addi tion bulbs was practically quantitative could be shown by pumping down the system behind stopcock No. 4. After closing Nos. 1 and 2 there was scarcely a movement of the manometer meniscus when stopcock No. 4 was opened after sealing off the addition bulbs. The hydrogen chloride addition bulbs were then sealed to the manifold shown in Figure £. This manifold was then connected to the equilibration flask and to the manometer and vacuum line. When it was desired to admit hydrogen chloride to the system the stopcock on the equilibration flask was closed. An Alnico magnet was used to lift the small glass enclosed 41

Sealed here after filling and freezing To hydrogen chloride - — ^ ' and vacuum line Asbestos board ( / / / / / / ; 7” ’/ / /?,'// ST A

Cylindrical Dewar flask

Liquid nitrogen

GURE 11

HYDROGEN CHLORIDE ADDITION BATH

(SHOWN IN FILLING POSITION) ~ '/z Scale 42 magnets. The small magnet was then allowed to drop and break the tip, admitting the gas to the system. The stop cock to the equilibration flask was then opened. This same method was used to fill bulbs with dry oxygen for the contamination studies. There was not, how ever, a quantitative transfer from the metering bulb to the bulbs immersed in liquid nitrogen since oxygen has a con siderable vapor pressure at the temperature of boiling nitrogen. The pressure before and after sealing was noted, however, and the amount of oxygen added could be calculated. 3. Aromatic Hydrocarbons 4. Benzene. The benzene used was Mallinckrodt, C. P., thiophene-free. The constant boiling middle cut was taken off a Podbilniak column, the still pot of which contained the deep blue ketyl formed by sodium-potassium alloy with benzo- 33 phenone. Since the color of the ketyl is destroyed by

33. Louis Fieser, Experiments in Organic Chemistry, Part II, 2nd ed., N. Y. Heath and Co., P 396. oxygen or moisture its presence during distillation is a "running” indication of purity. This middle cut benzene was then transferred to a reflux column and refluxed over the sodium alloy-benzophenone ketyl under an atmosphere of dry nitrogen. The middle portion was distilled into a carefully dried storage 43 vessel as indicated in Figure 12. The benzene boiling point was 79.4°C. at 74.32 cm, of mercury compared to the handbook value of &0.1°C. at 760 cm. of mercury. The refractive index was 1.5016 at 20°C; the literature gives the value 1.5017 at the same « temperature; The benzene was next frozen in the flask by immers ing the vessel in a Dry Ice-acetone bath. The storage flask was then connected to the vacuum line and degassed. After degassing and subsequent thawing the solvent was added to the equilibration flask by a tube reaching to the bottom of the storage flask. The vapor pressure exerted by benzene above the liquid in the vessel was sufficient to force the hydrocarbon into the evacuated equilibration flask to which aluminum chloride had already been added. The amount of benzene added was determined by weighing the. equilibrium flask before and after addition. b. Toluene. Toluene, (Baker and Adamson), was treated in the manner just described for benzene. It did not, of course, freeze when cooled to Dry Ice temperature, but was also degassed by pumping on the cooled storage flask. The boiling point range was 109.7°-,9°C. at.74.34 cm. of mercury compared to the literature boiling point of 110.$°C. at 760 cm. of mercury. The refractive index at Podbilniak Middle Degassing Equilibration Solvent and stoppage Column Cut flask flask

Liquid N trap

Pumping system

FIGURE 1 * BLOCK DIAGRAM FOR PURIFICATION AND ADDITION OF SOLVENT TO SYSTEM 45

20°C. was 1.4953 compared to the handbook value of 1.4955. G. Mesitylene. Mesitylene, obtained from the University of Illinois, was stored over sodium-potassium alloy and then distilled in a small column over the ketyl described above, taking the boiling range l63.&°- 163.9°C. at 741 ran. mercury. This was then prepared as was benzene, but sodium-potassium alloy alone, not the ketyl, was used in the final distillation.

The refractive index of the product used was 1.4969 at 20°C. compared to the literature value of 1.4912. It is probable that there was a small admixture of the other tri- methylbenzenes. Efforts to improve the purity by forming the sulfonic acid, separating and hydrolizing the product to isolate the pure isomer made no improvement. 4. Benzophenone for use in the experiments reported in Preliminary Observations. Benzophenone, (Mallinckrodt, C. P. ) was purified in either one of two ways: (a) frac tional distillation under reduced pressure, and (b) frac tional crystallization. In the first method the middle third of distilled product was collected and stored under a dry nitrogen atmosphere.

The fractional crystallization was effected as follows: Benzophenone was supported on a porous filter disk within a pyrex tube and melted with the aid of a steam 46

jacket. Dry nitrogen was then forced through the sintered glass disk from below, agitating the melt and assisting incipient crystallization. When one half of the material had solidified the flow of dry nitrogen was reversed and

the liquid benzophenone above the filter was then remelted and subsequently forced through the filter to a collection bulb. The purified benzophenone was most conveniently handled with a hypodermic syringe; when pure, the super cooled liquid had little tendency to solidify. The method of introducing the benzophenone was by addition of a weighed amount of benzophenone to a bulb, addition of a known weight of benzene to the bulb, agitation to effect solution, and addition to the equilibrium flask under dry nitrogen pressure. This addition bulb was then flushed with two weighed portions of benzene, again under the inert nitrogen atmosphere. 5. Miscellaneous, (a) The oxygen, (Linde), used in the contaminant studies, was treated as described under the hydrogen chloride section. (b) Water for the deliberate contaminant studies was intro duced by weighing drops of double distilled water into a the bulb of/hydrogen chloride addition type and added to the system as a vapor over the slurry. For another benzene run and for the toluene run it was introduced by adding known 47 0 1 weights of water saturated solvent. Simons and Kipp give

34. J. H. Simons and E. M. Kipp, I. and E. Chem., Anal. Ed. 12, 323 (1941). the value 0.067% by weight for water in benzene at 25°C.

The solubility of water in toluene at 2$°C. is 0.053%^.

35. C. K. Rosenbaum and J. H. Walton, il. Am. Chem. Soc., $2, 3563 (1930).

These moisture-saturated-solvent additions were made in reverse through the sampling device and flushed in with dry solvent. (c) For flushing the dry box and other equipment and main taining an inert atmosphere during distillations dry nitro gen was required. The nitrogen, (Linde oil-pumped), was monitored by passing it through a train of gas washing and drying bulbs containing ascarite, magnesium perchlorate, the sodium-potassium ketyl with benzophenone in xylene solution, mineral oil, and finally activated charcoal. From the take off manifold the gas passed through a column containing phosphoric anhydride. C. Operational Procedures. Preliminary. All of the glass equipment was cleaned with alcoholic potassium hydro xide cleaning solution, well rinsed with distilled water, and then dried in a 120°C. oven forseveral hours. 43

Dow-Corning high vacuum silicone grease was used on all joints and stopcocks in the aluminum chloride sublima tion equipment. The stopcocks of the equilibration flask and all stopcocks and joints exposed to aromatic hydro carbon vapors were covered with starch-glycerol-d-mannitol grease.

Traps used in the sublimation and distillation equip ment were cooled with liquid nitrogen. Starting a run. The equilibration flask, fitted with a magnetic stirring bar, and the aluminum chloride sublima tion manifold were connected to the vacuum system consisting of a roughing pump, mercury diffusion pump, traps and a McLeod gage. Aluminum chloride was then added to the equil ibration flask by the three fold vacuum sublimation method described in the aluminum chloride preparation section. After warming to room temperature and drying the out side of the equilibration flask it was weighed. The equilibra tion flask was then connected to the aromatic solvent storage bulb which had been charged with solvent during the sublima* tion. The connecting link between the equilibration flask and the storage vessel was brush-flamed and pumped out. The stopcocks between the storage bulb and the flask were then opened and the solvent forced in by its own vapor pressure. (For the less volatile mesitylene the pressure in the storage bulb was increased by wanning the vapor layer.) 49

The equilibration flask was again weighed and clamped in the constant temperature bath. The hydrogen chloride manifold was then connected between the equilibration flask and the line to the mano meter and pumping system. The bath enclosing the manifold was drained to facilitate flaming the manifold during evacua tion. After evacuating the manifold to a pressure below -5 10 cm. of mercury the stopcock to the pumping system was closed. The constant temperature bath containing the hydrogen chloride manifold was maintained at a temperature one half a degree higher than the bath containing the equilibration flask to prevent condensation of hydrocarbon in the manifold. The system proper then consisted of an equilibration flask containing a slurry of hydrocarbon and aluminum chlor ide, the hydrogen chloride manifold, and a mercury manometer to indicate equilibrium conditions. Sampling. When the manometer indicated equilibrium conditions the magnetic stirrer was shut off and the slurry allowed to settle for about an hour before withdrawing samples. The sampling bulbs shown in Figure 7 were evacuated through the side arm, sealed and weighed. They were then affixed to the sampling tube of the equilibration flask by the 5/20 standard taper joints. Samples of liquid were then forced into the sample bulbs by the pressure difference existing between the 50 two containers. After weighing, the samples were hydrolized by admitting water through the top inlet tube and then transferred to Erlenmeyer flasks for analysis. Prior to sampling a small quantity of liquid was withdrawn to clear the capillary of the sampling tube. Hydrogen chloride additions. When it was desired to change the composition of the system by adding hydrogen chloride the stopcock on the equilibration flask leading to the mani fold was closed. One of the magnetic hammers was lifted with an external magnet and allowed to drop, breaking the glass tip and admitting hydrogen chloride to the manifold. The stopcock to the flask was then opened and the hydrogen chloride dissolved by the swirling liquid. Successive read ings of the manometer indicated when equilibrium was obtained. D. Analytical Procedures. The information required from analyses was the concentration of aluminum chloride and hydrogen chloride. The fact that these might be combined in a complex with the solvent was unimportant since hydrolysis destroyed these complexes. Aluminum chloride was determined as aluminum ion and hydrogen chloride as hydrogen ion according to the following 36 method of Snyder.

36. L. J. Snyder, I.and E. Chan., Anal. Ed. 17, 37 (1945). 51

The weighed sample was washed into an Erlenmeyer flask and titrated in the presence of sodium potassium tartrate to the phenolphthalein end point with standard barium hydroxide. This gave free acid and aluminum content. Addition of potassium fluoride released potassium hydroxide from the aluminum hydroxide formed in the titration with standard base. Standardized hydrochloric acid was then used to titrate the hydroxide to the disappearance of the pink color. The second titration gave the aluminum concentration. Free acid was indicated by the difference between the results of the two titrations. The data are presented in the tables and graphs as +++ ^ + 3 molalities of kl x lCr and H x 10 . More exactly these represent aluminum content and hydrogen content as the con centration of gram atoms of aluminum per thousand grams of solvent and moles of hydrogen chloride per thousand grams of solvent. For the work with benzophenone and the other data of the Preliminary Observations section aluminum chloride was determined as the S-hydroxy quinolate gravimetrically by 37 the method described in Koltoff and Sandell.

37. I. M. Koltoff and E. B. Sandell, Textbook of Inorganic Analysis, N. Y., Macmillan, 193o> P 306. 52

E. Summary of Manipulatory Difficulties Encountered. The most serious difficulties met in this work were those concerned with moisture and other contaminants and their elimination. For this reason aluminum chloride was sublimed directly into the equilibration flask and the addition tube sealed with a flame. Caution had to be exercised in preparing the solvents to keep them dry. All glassware was brush flamed and evacu ated to remove occluded moisture and the distillations were carried out under a dry nitrogen atmosphere. Stopcock grease proved to be troublesome. Even sili cone grease tended to dissolve in the hydrocarbons and stop cocks developed leaks in time. Fluorocarbon greases were inert, but proved unsatisfactory for stopcocks that had to be manipulated frequently as it tended to "pill". The number of stopcocks and joints in the system should be kept at a minimum. The use of a magnetic stirrer eliminated a troublesome experimental difficulty. It pro vided efficient stirring and helped eliminate a joint where contaminants might enter. The vacuum stopcocks and joints were hand lapped with a slurry of 3-F carborundum and water to ensure good fits. These were marked to avoid mixing barrels and plugs.

Sealing the sampling device in a fixed position helped to avoid another possible source of a leak, but it 53 left the sampling method somewhat inflexible. Wien much "red-oil” was formed in the bottom of the flask droplets of the dark, oily substance were sometimes entrained in the sample. These samples were found to be much higher in aluminum chloride and had to be discarded in the data plots. The sampling method made it impossible to withdraw samples of the rtred-oil" for analysis. The concentrations of aluminum chloride and hydrogen chloride were so low that analytical procedures were unsat isfactory unless samples of about seven or more grams were withdrawn. VI. Data

A. Benzene as Solvent. The equilibrium studies in benzene are presented in Tables VI, VII, VIII, and shown graphically in Figures 13 through 16. a. No complex without promoter. Table VI and Figure 13 demonstrate that there is no coordination of aluminum chlor ide with hydrogen chloride in benzene at 25°C. in the absence of a promoter. The dashed line following water addition shows a break due to incomplete addition of water in the first attempt to add that reagent. The ratio of aluminum chloride to hydrogen chloride then became 1.06 when the system was made 0.037 molal with respect to water. The actual concen tration of water in the solution was probably lower. 54

TABLE VI

Promoting effect of Water on Coordination of Aluminum Chloride with Hydrogen Chloride in Benzene at 20°C.

+ + + Molality A1 Molality H 3 xlO xlO3

5.2 5.5 1.6 5.1 13.3 5.1 27.6 5.4 23.3 5.1 33.7 5.5 43.4 5.3 66.2 6.2 40.4 6.4 37.9 26.5 20.0

* At this point the system was made 0.037 molal with respect to water. 55

FIGURE 13 BENZENE, ALUMINUM CHLORIDE, HYDROGEN CHLORIDE, WITH SUBSEQUENT WATER ADDITION 25 °C.

Slope = 1.06

/° 'o------*- -XT - 0 - 0 > ( j

J______I______i______I______I 2 3 4 5 6

Molality H+ x I02 b. Complex with promoter. Table VII and Figure 14 show the co-ordination between aluminum chloride and hydrogen chloride in benzene at 25°C. as influenced by the presence of water. It is assumed that traces of moisture or other contaminant were present at the start of the runs. The effect of oxygen is also demonstrated in one of the runs, and also shown to be a promoter for complex formation. Table VIII and Figure 15 and 16 show the effect of water on the solubility of aluminum chloride in benzene at

25°C. with the subsequent effects of hydrogen chloride and water. For this run water was added to the bulk of the solution rather than as vapor diluent as in the previous runs. As seen in Figure 16 the initial addition of water caused a ratio of aluminum chloride to water of 1.44 and a ratio of 0.57 for subsequent water additions. c. Equilibrium constant. Taking the ratio 0.14 for aluminum chloride-hydrogen chloride the equilibrium constant for the formation of tetrachloroaluminic acid in benzene solution in the presence of traces of promoter. promoter A1C13 (s) + HC1 2. — HA1C14 (or HAIC^OH)

XT - 0 • 14 _ ^ 1 £ K " U.W" " 0#lb* Toluene as Solvent. The toluene data are summarized in Tables IX and X shown graphically in Figures 1? and IS. 57

TABLE VII

Co-ordination of Hydrogen Chloride with Aluminum Chloride in the presence of Water in Benzene at 25°C.

Molality Al+++ Molality H* Legend Slope,mAlCl^/mHCl xl03 xlCK 6.6 0.3 7.0 0.0 7.7 6.2 0.14 6.3 11.7 1 0 9.6 10.1

10.5 14.7 10.9 15.1 11.4 20.7 0.15

5.5 1.6 5.4 3.0 0.13 6.2 7.4 6.4 10.1 6.7 9.6 -C1 6.6 25.1 6.9 26.5 9.7 20.5 10.4 16.6 X 10.4 19.0 — — — — — _]£ 10.9 20.6 11.1 25.3 0.16 10.6 24.2 12.5 34.4 16.6 56.6 - -E1 16.0 46.1 17.6 49.4 a 1- System made 0.004 molal with respect to water. B- HC1 added again C - Changed HC1 manifolds to increase concentration range. D- System made 0.013 molal with respect to water. E- HC1 added again. El- O2 added. MOLALITY Al+++ x I0 3 OAIY x IO x + H MOLALITY EZN, LMNM CHLORIDE, ALUMINUM BENZENE, YRGN HOIE SHOWING CHLORIDE HYDROGEN FET F AE AD OXYGEN AND WATER OF EFFECT 25° C.25° Slopes: Slopes: FIGURE FIGURE C-C7 B 0.15 B/ B- A-A7 E-E7 i* 0.18 0.13 0.14

TABLE VIII

Effect of Water on the Solubility of Aluminum Chloride in Benzene with Subsequent effects of Hydrogen Chloride and

Water at 25°C.

Molalities xlO^ Al+++ H+ H20 Legend

S. 5 O.S 0.0 S.7 -0.6 0.0 x a.4 0.4 O.o i o.7 -o.i i.a 11.4 - 1 4 ® 12.0 0.9 1.6 11.2 0.6 4.0 12.5 -1.2 4.0 0 12.3 -0.3 4.0 13.2 - 6.0 13.6 -o.a 6.0 q 1 2.a 1.0 6.0 12.9 14.4 6.7 & 13.6 3.S 15.0 23.4 15.0 34.0 A 15-.1 17.0 15.3 36.2 A 15.3 30.a 16.2 31.4 16.5 33.1 rrj 16.2 - u I 10 o 10 MOLALITY Al 12 14 8 -2

0 L J 8 L J 12 l_ J OAIY +x 03 I0 x H+ MOLALITY 16 _ L_ ±_ HOIE N WTR T C. ° 5 2 AT WATER HYDROGEN AND OFCHLORIDE ADDITION BENZENE IN SUBSEQUENT CHLORIDE ALUMINUM OF EET F AE O SOLUBILITY ON WATER OF EEFECT Iiil solubility Initial x Wtr addition Water □ addition chloride Hydrogen A ae addition Water o 20 I L I I J 24 FIGURE FIGURE LP = 0.13 =SLOPE

15 L_ J 32

L l _ 36

05 o to + + + O MOLALITY AI 0 OUIIY F LMNM HOIE IN CHLORIDE ALUMINUM OF SOLUBILITY EZN A 2°. AS 25°C. AT BENZENE H PEEC O WATER OF PRESENCE THE OAIY H20 MOLALITY 61 IUE 16 FIGURE 8 x

103 INFLUENCED 10 12 BY

a » Toluene versus time. When toluene is refluxed over

aluminum chloride disporportionation takes place. It was believed that this process might proceed at a slower rate at room temperature and for this reason a time study of the system toluene-aluminum chloride was undertaken. This is illustrated by the data of Table IX and Figures 17. The effect of water addition is shown at .the end of the run. (See Discussion, Evidence for dimer,

P 80.) b. Complex with promoter. The solubility of aluminum chloride in toluene at 25°C. increases with time at the rate of 2.66xlO“5 moles per hour. At the same time the concentration of hydrogen chloride in the system increases -5 1.47 x 10 ' moles per hour. The molality of aluminum chloride increased by 0.0064 for a 0.0060 molality addition of water, but when a time correction is applied the molality increase is reduced to 0.0076 for a ratio of 1.27 moles aluminum chloride per mole water. The hydrogen chloride increase was one third that of aluminum chloride for the same water increase. t. Table X and Figure 16 show the coordination between aluminum chloride and hydrogen chloride in toluene at 25>°C. The broken line show the data uncorrected for time and the solid curve shows the time correction of Table IX applied to the same data. The equilibrium constant for the formation 63

TABLE IX

Effect of Time on the Solubility of Aluminum Chloride in Toluene at 25°C. with effect of subsequent Water addition,

Molalities xlO 3

Ai+++ H+ time, hours

7.3 1.3 2. 5 hours 7.2 1.3 2.5 hours 6.5 1.1 20 hours S.S 0.7 20 hours 6.6 1.3 20 hours 9.3 1.4 45 hhours 9.6 1.1 45 hours 9.1 1.3 45 hours 10.7 2.2 93 hours 10.4 2.9 93 hours 19.2 3.5 121 hours from h 20

16.7 5.1 121 hours from H20 addition.

* System made 0.006 molal with respect to water AlCl3 in C^H^CH^, 2.B6xl0“5 moles per hour HC1 in C^HtjCH^, 1 .47x10”^ moles per hour MOLALITY Al *** & H+x I03 20 LMNM HOIE N OUN AT TOLUENE IN CHLORIDE ALUMINUM FET F IE N H SLBLT OF SOLUBILITY THE ON TIME OF EFFECT 5C WT SBEUN WTR ADDITION WATER SUBSEQUENT WITH 25°C. 20 IUE 17 FIGURE 40 IE N HOURS IN TIME +wt time with H+ 60 80

100 120 65

TABLE X

Co-ordination of Aluminum Chloride with Hydrogen Chloride in Toluene at 25°C.

3 Molalities xlO Time correction Corrected Al++* H+ Time, hours Al+++ H+ Al+++ H+

S.3 0.6 21 hours -0.6 -0.3 7.7 0.3 £.4 0.2 21 hours -0.6 -0.3 7.3 -0.1 9.3 1.9 41.5 hours -1.2 -0.6 3.1 1.3 9.6 0.9 41.5 hours -1.2 -0.6 3.4 0.3 15.4 12.5 46.5 hours -1.3 -0.7 14.1 11.8 19.5 19.3 6 5 .O hours -1.3 -0.7 17.6 13.9 13.4 20.4 6 5 .O hours -1.9 -0.9 16.5 19.5 23.7 23.4 71.5 hours -2.0 -1.0 21.7 27.4 26.3 32.3 71.5 hours -2.0 -1.0 24.3 31.3 to O MOLALITY Al+++ x 24 0 2 12 - - OAIY *x 0 * I03 x H* MOLALITY Slope= 0.57 16

OUIIY F LMNM HOIE IN CHLORIDE ALUMINUM OF SOLUBILITY OUN A 2°. S NLECD BY CHLORIDE INFLUENCED HYDROGEN AS 25°C. AT TOLUENE 24 norce fr time for Uncorrected o Tm creto applied correction Time x lp =0. 0 .5 =Slope0 832 28 FIGURE FIGURE 18

of tetrachloroaluminic acid in toluene is 1.32 for the dash ed curve and 1.00 for the time corrected data. G. Mesitylene as Solvent. The data for the work with mesitylene are summarized in Table XI t?o XIII. and Figures 19 and 20. a. No complex without promoter. Table XI and Figure 19 show the effect of time on the system aluminum chloride- mesitylene at 25°C. followed by air addition. There was no co-ordination between aluminum chloride and the solvent until air was admitted and then aluminum chloride dissolved at the rate of 4.05 x 10“^ moles per hour. b. Complex. Table XII and Figure 20 show the effect of the concentration of hydrogen chloride on the solubility of aluminum chloride in mesitylene at 25°C. The first two add itions of hydrogen chloride caused an increase in the solub ility of aluminum chloride, but the third addition resulted in"a marked reduction of the aluminum salt concentration in the body of the solution. Removal of hydrogen chloride by pumping on the system had the effect of replacing a portion of the aluminum chloride in the solution. c. Equilibrium constant. Since the second liquid phase com plicated the system and the indicated ratio for aluminum chloride-hydrogen chloride was greater than unity, no equil ibrium constant was calculated for the mesitylene system. TABLE XI

The Solubility of Aluminum Chloride in Mesit-ylene Versus Time at 25°C. with Subsequent Air Admission.

3 Molalities xlO time, hours

Ai+++ H+

8.4 2.1 5.5 hours 8.2 3.0 5.5 hours 8.7 0.6 5.5 hours 8.5 1.1 20.5 hours 8.9 0.6 20.5 hours 8.3 3.0 20.5 hours 8.5 1.8 29 hours 8.3 0.4 29 hours 8.4 2.7 43.5 hours 12.1 0.6 53 hours 11.1 -0.7 53 hours 17.5 0.2 66 hours 19.9 1.3 66 hours 21.9 1.8 75.5 hours

* Air entered. lO MOLALITY Al + + + x 10 22 20 _ 4 - 4 1 20 050 30 IE N HOURS IN TIME LMNM HOIE N MESITYLENE IN CHLORIDE ALUMINUM I AMSIN - ADMISSION AIR S TM A 2°. IH SUBSEQUENT WITH 25°C. AT TIME VS. 60 FIGURE FIGURE 080 70 19

TABLE XII

Solubility of Aluminum Chloride in Mesitylene at 25°C. as affected by Hydrogen Chloride Addition and Subsequent Removal by Pumping.

Molalities xlO^ Al+++ H+

9.9 1.3 11.7 3.4 13.9 4.3 13.4 4.5 14.0 4.9 7.7 5.3 7.9 5.6 7.7 4.9 7.2 4.9 9.5 2.7 9.7 3.2

A- First Hydrogen Chloride Addition. B- Third Hydrogen Chloride Addition.

C- Pumped on System for 15 Minutes. o G,

ALUMINUM CHLORIDE IN MESITYLENE AT 25°C. WITH ADDED HYDROGEN CHLORIDE, FOLLOWED BY PUMPING

FIGURE 2 0

J______I______I______I______L 2 3 4 5 6

MOLALITY H+ x I03

\ 72 d. Effect of oxygen on aluminum chloride-mesitylene system. Table XIII shows the effect of oxygen concentration on the solubility of aluminum chloride in mesitylene. The addition of oxygen sufficient to make the oxygen concentra tion in mesitylene 0.026# molal caused an increase in the aluminum chloride concentration in mesitylene of 0.0375 moles for a mole ratio of aluminum chloride to oxygen of 1.40. A small amount of a heavier second liquid phase re sulted. A second oxygen addition caused the formation of considerable T,red oil” with a resultant decrease in the -■to that concentration/before any oxygen addition. This decrease had a mole ratio of aluminum chloride to oxygen of -1.00. Pumping on the system to effect a decrease in oxygen con centration caused an increase in the aluminum chloride concentration in the solvent. (Those samples marked x are. doubtful due to the obvious traces of red oil in these samples.) 73

TABLE XIII

Effect of Oxygen on Aluminum Chloride-Mesitylene System at 25°C.

Molality Al+++ x 10^ Molality 0£ x 10^

13.7 0.0 14.5 0.0 13.3 0.0 49.3 26.S 51.7 26.8 x 64.5 26.8 16.5 63.5 x 17.6 63.5 12.7 63.5 — _ _ — — — _____ — * 17.0 (?) x 32.4 (?) x 43.7 (?)

^Pumped on system for 15 minutes. 74

VI. Discussion of Results

Sl* 12. Hydrogen chloride-aluminum chloride addition compound. The inability to form the addition complex, tetrachloroaluminic acid, from aluminum chloride and hydrogen chloride in 1 the absence of a suitable solvent may be explained by the following reasoning. Aluminum chloride is known to exist in 33 both the solid and vapor states as the dimer.

33. Thomas, loc.cit., p. 12-16.

The structure I and II, II being preferred at present, indicate hydrogen chloride would have to rupture the dotted chelate bonds to form HAICI^.

I II Since the dimer is stable even in the vapor state the free energy of formation of the hydrogen chloride addition compound may be insufficient to rupture the strong chelate bonds present in the dimer. b. High aluminum chloride-benzophenenone ratios. A possible explanation for ratios of aluminum chloride to benzophenone greater than unity may be given by either or both of two reasonings. The first is the presence of contaminants that 75

exhibit a promoting effect on complex formations. This is demonstrated by the different initial solubilities of aluminum chloride in benzene and the greater ratios associ ated with those higher initial values. A second explanation is that the complex formed is itself a solvent for aluminum chloride and thus typical of Friedel-Crafts "red oil"\

•X* *X• 0:C::O: + Al:X: 0:C::0:A1:X: A1C1, $ 4:" 4s" — ^

02COA12C16 AlCl^, 02COA13C19 =* etc. c, Inorganic catalytic couples. The highly colored complexes produced when mercury and mercurous and mercuric chlorides were added to mixtures of benzophenone, aluminum chloride, and benzene may indicate a catalytic couple. These systems had abnormally high aluminum chloride concentrations. Numerous couples of aluminum chloride with inorganic halides 39 are known.

39. C. A. Thomas, loc.cit., p. 563-70. d. Repeated sublimation of aluminum chloride. The data of Table II showing the refining effect of repeated sublima tions of aluminum chloride in an inert atmosphere corroborate the work of Stevenson and Beeck2^ and the note by Thomas^0 76

40. G. A. Thomas, loe.cit., p. 73. on the difficulty of obtaining anhydrous aluminum chloride and benzene. j. Importance of promoters. The disproportionation of aro matic hydrocarbons treated with aluminum chloride and hydro- 5 gen chloride as reported by Ipatieff and Komerewsky , and £ Anschutz and Immersdorf may well have been promoted by traces of water or air. The alkylation and isomerization studies of Berry and Reid^, Pines and Wackher2^, Schmerling^, and Lien2^ indi cates the need for a promoter to assist the aluminum chloride- hydrogen chloride couple. Lien notes that although there is a small measureable rate for the isomerization of alkanes by the catalyst couple industrial conditions were employed and the possibility for a small moisture contamination was present. The present study demonstrated that no increased solu bility of aluminum chloride in benzene or mesitylene occurred with hydrogen chloride unless a promoter was added. This is in disagreement with the lower temperature Henry’s law stud ies of Brown and Pearsall^ who claimed complexes of aluminum chloride with hydrogen chloride in toluene. However; they make one open air transfer of their purified aluminum chloride to the apparatus; this is probably sufficient to introduce enough air or moisture for the promoter effect. They may 77

have found the complexes even in the absence of a promoter due to increased thermal stability at the lower tempera tures.

When complexes with promoted hydrogen chloride did

form the data displayed an agreement with that of Brown and Pearsall in toluene. They found a l/l ratio of aluminum chloride to hydrogen chloride at -B0°C. and a 2/1 ratio at -45.5°C. Brown and Pearsall explained these ratios at low temperatures by the formation of the salts ArH A1C1. at o 4 -BO C. and ArH’^A^Cl,.,'" at -45.5-0. They believed this process might be continued to ArH+AlxCl^x+^. The present data indicate a 1/2 ratio of aluminum chloride to hydrogen chloride at 25°G. for toluene. This is in agreement with the concept of greater stability for the complex at lower temperatures.

Since oxygen was found to increase the solubility of aluminum chloride in benzene and mesitylene it is to be inferred that it is also a promoter for complex formation with hydrogen chloride. f . Relative basicity of solvent. An increased tendency for the reaction AlCl-j + HC1 HAICI^ to go to the right in more basic solvents is shown by the aluminum chloride- hydrogen chloride ratios in benzene, toluene, and mesitylene. These were respectively 0.14, 0.50, and 1.12. n

The increased bacisity of the series benzene, toluene, ortho and para xylene, and mesitylene was demonstrated by Benesi and Hildebrand^* by studies of the absorption band

41. H. A. Benesi and J. H. Hildebrand, J. Am. Chem. Soc., 71, 2703 (1949). ~n. " "" _ ~ l_ “ ~ spectra on the l/l mole ratio complexes of these aromatic molecules with iodine. The iodine-mesitylene complex was found to be the most stable and the iodine-benzene complex the least stable. Condon found that the rates of alkylation and halogen- ation of the alkyl substituted benzenes to be in line with hf the increased basicity of the higher substituted derivatives/

42. F. E. Condon, J. Am. Chem. Soc., 70, 1963, 2265 (194#). il‘ The role of water and oxygen. The specific role of water and oxygen in influencing the catalytic behavior of aluminum chloride and complex formation is still unknown. Three possible explanations are offered. 1. The role is that of a catalyst which is necessary to over come the energy of activation for the formation of the complex Information that seems to indicate this is the data shown in Figure 14. The ratios of aluminum chloride to hydrogen chloride were almost identical before and after the addition of small amounts of water, but the actual concentration of 79

aluminum chloride was increased by the addition of water. 2. The role may be that of the formation of a new cataly- 29 tic species. This is supported by the data of Beeck and the possibility of the catalytic species Al2Cl^__n jOHn , (l-n-5). The hydrate formation by an acid-base mechanism / also supports the changed catalytic species view. 3. The role might well be a combination of the two mentioned above.

Jj. Ternary complexes. The complexes found in the present work between hydrogen chloride and aluminum chloride may be interpreted to involve the solvent as pictured by Brown\ The equilibrium constants found would be unaltered by this consideration, however, due to the large excess of the solvent. The concentration of the solvent would be essentially unchanged by the small amount of complex formed and would therefor be represented in the mass action expression by unity as is solid aluminum chloride. lL* Evidence for hydrates. Table VIII and Figure 1$ demonstrat ed that there was no marked increase in hydrogen chloride concentration in benzene accompanying the increased aluminum chloride concentration caused by the addition of water. This 26c verifies data of Pines and Wackher who found that the addition of moisture formed some HOAlClg which promoted catalytic activity, but all the hydrogen chloride predicted by stoichiometry was not evolved. Some hydrate formation by go

an acid-base mechanism is indicated.

H:0: + Al:X: H:0 : Al:X: # :X: "* H :X: *'

J_. Evidence for dimer. From the toluene-aluminum chloride time study it seems probable that aluminum chloride dissolves in these aromatic solvents as the dimer. Table IX indicates that aluminum chloride dissolves in toluene at the rate of 2.£6 x 10”5 moles per hour. This resulted in a concomitant increase in hydrogen chloride concentration, but the rate _ 5 was 1.47 x 10 ^ moles per hour. The same type of study in mesitylene, Table XI, show ed no increased solubility until moist air was admitted. In the toluene run the aluminum ion concentration increased and the hydrogen ion concentration decreased between the first two sets of samples. An increase in aluminum ion with an accompanying decrease in hydrogen ion concentration has been shown to be an effect typical of moisture. This system may therefore have been contaminated in the first sampling. The solubilizing effect of the promoter might then be A ^ C l ^ ^ + H. pro. pro. AlgCl^ + HG1, the combined effect of the promoter and hydrogen halide effecting further solution.

T,Re(* oil" complication. In the later stages of the ben zene runs the surface of the solid aluminum chloride became d i

darker and the bulk of the solution assumed an amber hue. In toluene the aluminum chloride acquired a yellow tint upon the introduction of the solvent. In time the body of the solution became yellow gold in color and a small amount of a dark, oily phase was formed. The solution acquired a deep yellow color when mesitylene was added to aluminum chloride. The color of the solution became darker as the run progressed and about one tenth of the liquid was a dark, red-brown, second phase. The colors of the solutions are probably due to partial solution of the "red oil" in the aromatic hydro carbon. These red oils are evidently ternary complexes between aluminum chloride, hydrogen chloride, and the solvent. Table XII and Figure 20 demonstrate this to be the case for the mesitylene system and indicate a distribution of aluminum chloride between the solution and the red oil. I. Distribution of aluminum chloride. As hydrogen chloride was added to the mesitylene-aluminum chloride slurry the ternary complex started to form and increased the concentra tion of aluminum chloride in the solution. When more hydro gen chloride was added more of the red oil was formed and the ternary complex was a better solvent for aluminum chloride than thedmesitylene. Then when part of the hydrogen chloride was removed by pumping off the system part of the complex was destroyed and some of the aluminum chloride so released went 32

back into the mesitylene solution. A1G1- ^ AlClo complex ' jg* A1C1 complex ■*(solid) (sol'n) ^ (red oil). This is substantiated by the work of Ulich and Heyne^.

43. H. Ulich and A. Heyne, Z. Elekrochem., 41, 509 (1935).

In alkylations they reasoned that since aluminum chloride is so difficulty soluble in aromatic hydrocarbons the reaction may proceed slowly on the surface of the aluminum chloride. The reaction products so formed dissolve aluminum chloride more effectively than the hydrocarbon with the resultant formation of a second liquid phase which contains aluminum chloride in the foim of a molecular compound with the re action products. The aluminum chloride so dissolved has a high catalytic activity and may catalyse the reaction with an alkyl halide-aluminum chloride complex,

m. Effect of oxygen on aluminum chloride-mesitylene system.

The effect of oxygen was first to increase the concentration of aluminum chloride in the solvent and then reduce it; removal of oxygen by pumping on the system had the effect of increasing the aluminum chloride concentration in mesitylene, This is apparant evidence for the triple equilibrium:

A1C13(S) ^ A1013-°2-SOlTen‘solutlon) ^ A 1 0 1 3 -62. so}vent (red oil). VIII. Future Problems

One of the more intriguing aspects of the present work was the appearance of a separate phase, particularly in the toluene and mesitylene systems. The composition and utilization of these "red oil" complexes has not been thoroughly investigated. Means to separate and investigate them would be useful. The use of absorption spectra might be efficacious as an analytical device on systems of the type encountered in this work. Evidence for stoichiometric combinations in the composition of the complexes might be found more effec tively in this than in any other way; however, cryoscopic studies on the complexes could be very helpful. A study of homogeneous alkylations using the aromatic hydrocarbonusolutions of aluminum chloride and / or aluminum chloride complexes might prove fruitful. A closely controlled study on the effect of moisture or oxygen in promoting the catalytic effect of aluminum chloride for alkylations or isomerizations should be of interest. Realizing the tremendous influence of moisture or air on aluminum chloride catalysed systems it might be well to reinvestigate conductivity studies of systems containing the aluminum halides. Since al'aminum bromide is more soluble in aromatic 34 hydrocarbons than the chloride, a similar study using the aluminum bromide, hydrogen bromide couple might prove simpler from an experimental standpoint. 35

IX. Summary

The equilibria of aluminum chloride and hydrogen chloride in benzene, toluene, and mesitylene have been studied.

There is no co-ordination between aluminum chloride and hydrogen chloride in benzene unless some promoter, (proton acceptor), such as water is added. The tendency for an aluminum chloride-hydrogen chloride-aromatic hydrocarbon ternary complex to form increases with increased basicity of the solvent. The effect of moisture and oxygen on the solubility of aluminum chloride in the aromatic hydrocarbons has been demonstrated. The ratios of aluminum chloride to hydrogen chloride in benzene, toluene, and mesitylene have been found to be 0.14> 0.50, 1.12, respectively. Equilibrium constants for the formation of tetrachloroaluminic acid (or complex of the solvent with the acid) are therefore 0.16 for benzene and 1.00 for toluene. The rapid disproportionation of mesitylene that occurs in the presence of aluminum chloride at the reflux tempera ture does not appear at room temperature over a period of several days in the absence of humid air. AUTOBIOGRAPHY

I, Lewis Delmar Swan, was born in Kansas City, Missouri, December 11, 1921. I received my secondary school education in the public schools of Xenia, Ohio. My undergraduate training was obtained at Miami Univer sity, from which I received the degree Bachelor of Arts in 1943. Following three years in the United States Army I returned to Miami University and was employed as a graduate assistant in the Department of Chemistry. By a liason program between Miami University and The Ohio State University I received the degree Master of Science from the latter institution in 194&. While completing the requirements for the degree Doctor of Philosophy I held appointments as Assistant and as Assistant Instructor in the Department of Chemistry at The Ohio State University and also held United States Navy, Office of Naval Research and du Pont Company fellowships.