[CONTRIBUTION FROM THE KEDZIE CHEMICAL LABORATORY hfICHIGAN STATE COLLEGE]
CONDENSATION OF ALIPHATIC ALCOHOLS WITH AROMATIC COMPOUNDS IN THE PRESENCE OF ALUMINUM CHLORIDE. 11. TERTIARY ALIPHATIC ALCOHOLS AND BENZENE R. C. HUSTON, W. B. FOX,
AND
M. N. BINDER
Received July 10, 1937; revised May 2, 1938
It has been shown that unsaturation of the alpha carbon atom of alcohols favors condensation of these compounds with aromatic hydrocarbons or phenols in the presence of anhydrous aluminum chloride. The unsaturation may be due to an aromatic ring1, a simple double bond2, or strain in a polymethylene ring3. A second factor which was found to influence the ease with which an alcoholic hydroxyl will combine with the hydrogen of an aromatic ring is the accumulation of alkyl radicals on the carbinol carbon. Under the experimental conditions described saturated primary aliphatic alcohols do not condense, simple secondary alcohols give a 25-30 per cent. yield of the secondary alkyl benzene, while tert.-butyl alcohol gives a 60-70 per cent. yield of trii~~ethylphenylmethane~. 5. The following alcohols were condensed with benzene : tert.-butyl alcohol, tert.-amyl alcohol, the three led-hexyl alcohols, and the seven tert.-heptyl alcohols. Physical constants were carefully determined and are discussed in their relationship to structure. EXPERIMENTAL
The technique used in all condensations was similar to t h a t described in an earlier paper4. One-eighth of a mole (0.5 equivalent) of AlCla (c.P. white) was suspended in 1.25 mole (5 equivalents) of thiophene-free benzene in a three-necked roundbottomed flask provided with mercury-sealed mechanical stirrer, a reflux condenser, and a dropping funnel. The mixture was vigorously stirred while0.25mole(l equivalent) of the carbinol was added drop by drop. The temperature was maintained at 20-30". The usual reaction phenomena were exhibited: hydrochloric acid was evolved, and the reaction mixture turned a deep red. After standing overnight, the mixture was decomposed with ice and a little hydrochloric acid. The benzene layer was removed, and the aqueous portion was extracted with ether. 1 HUSTON AND FRIEDEMANN, J . Am. Chem. Xoc., 38, 2527 (1916); 40, 785 (1918); HUSTON,ibid., 46, 2775 (1924). 2 HUSTON AND SAGER, ibid., 48, 1955 (1926). 3 HUSTONAND GOODEMOOT, ibid., 66, 2432 (1934). 4 HUSTON AND HSIEH,ibid., 68, 439 (1936). TZUKERWANIK, J . Gen. Chem. (U. S. S. R.), 6, 117,764, 767 (1935). 251
252
R. C. HUSTON, W. B. FOX, AND M. N. BINDER
Ether and benzene were removed from the combined extract by distillation and the residue was fractionated through a 30-cm. column, generally under reduced pressure. Trimethylcarbino1.-Yield of 2-methyl-2-phenylpropane,66570%. The residues from several condensations, boiling above 170", were combined and fractionated. T h a t portion which came over at 230-240" (736 mm.) solidified, and melted after recrystallization from alcohol a t 77-78' (white plates). It was identified as p-di-tert.-butylbenzene. Dimethylethylcarbino1.-After about half of the alcohol had been added, there was formed a dark-colored coagulum which made stirring difficult. When the temperature was allowed to rise to 30-32" this mass broke up, and the reaction proceeded with the elimination of much hydrochloric acid. The yield of 2-methyl-2phenylbutane' was approximately 60%. The small residue did not yield a constantboiling fraction. Dimethyl-n-propylcarbino1.-The 2-methyl-2-phenylpentane8, was collected a t 86-88' (15 mm.) in a yield of approximately 55%. At atmospheric pressure (745 mm.) i t boiled a t 205206". Dimethylisopropylcarbino1'J.-Fractionation was carried out a t 15 mm. A somewhat smaller yield of condensation product, 2-3-dimethyl-2-phenylbutane(b. p. 86-87' 15 mm.), was obtained (35%). This decrease in yield is attributed t o the accumulation of radicals on a carbon adjacent to the carbinol carbon. Anal. Calc'd for C12H18: C, 88.81; H, 11.19; mol. wt., 162. Found: C, 88.69; H, 11.13; mol. wt., 165. Methyldiethylcarbino1.-This carbinol was prepared from ethylmagnesium bromide and ethyl acetatelo. Condensation with benzene gave a 40% yield of 3-methyl3-phenylpentane11 which came over at 86-88" (15 mm.). Dimethyl-n-butylcarbinol1~.-Duringthe extraction of the aqueous portion of the reaction product with ether an emulsion was formed, which was broken up by the addition of hydrochloric acid. After removal of the ether and benzene from the combined extracts, fractionation was carried out at 20 mm. The first fraction (30-106") gave positive tests for unsaturation and for chloride. From i t was isolated a small amount of 2-chloro-2-methylhexane13; b.p. 132' (740 mm.), 39-40" (20 mm.); n:, 1.4210. As a check the chloride was prepared from the carbinol by saturation with dry hydrochloric acid. The main product of the condensation, 2-methyl-2-phenylhexane1came over a t 106-109" (20 mm.); yield 45%. Anal. Calc'd for ClaHzo: C, 88.63; HI 11.37; mol. wt., 176. Found: C, 88.61; H, 11.44; mol. wt., 169. Dimethylisobutylcarbin011~.-A considerable fraction came over a t 33-40' (20 mm.). 6 VERLEY,Bull. SOC. chim., [3], 19, 72 (1898); BOEDTKER, ibid., [3], 31, 966 (1904); SCHRAMM, Monatsh., 9,615 (1888);SHOESMITH ANDMACKIE, J . Chem. Soc., 2334 (1938). 7 GLEDITSCH, Bull. SOC. chim., [3], 36, 1094 (1906). 8 SCHREINER, J . prakt. Chem., [2], 82, 293 (1910). 9 DELACRE, Bull. acad. roy. Belg., 1906, 7; LINDER,Monatsh., 32, 419 (1911). 10 HENRY,Rec. trav. chim., 26, 94 (1907). 11 SCHREINER, J . prakt. Chem., [2], 82, 295 (1910). 12 WHITMORE AXD CHURCH, J . Am. Chem. Soe., 66, 1119 (1933). 1: DEWAEL, Bull. acad. TOY. Belg., 1908, 957. 14 EDGAR, CALINGAERT, AND MARKER, J . Am. Chem. Soc., 61, 1483 (1929).
TERTIARY ALIPHATIC ALCOHOLS AND BENZENE
253
This gave a posithe test for unsaturation but consisted for the most part of 2-chloro2,4-dimethylpentane which boiled after repeated fractionation at 33-34' (20 mm.). When boiled a t atmospheric pressure i t decomposedls, liberating hydrochloric acid; n:) 1.4239. The condensation product of the carbinol and benzene came over at 100-102" (20 mm.), 216-218" (746 mm.); n?', 1.4940. The yield of 2,4-dimethyl2-phenylpentane16 was approximately 30%. Dirnethyl-sec.-butyl-carbinol~4.-From the first fraction, which contained some unsaturated compounds, there was isolated 2-chloro-2,3-dimethylpentaneboiling a t 38-39' (20 mm.); n:, 1.4264; yield, 10%. The main product of condensation, 2,3-dimethyl-2-phenylpentane,came over a t 105-107" (20 mm.); yield, 20%. Anal. Calc'd for C13H20: C, 88.63; H, 11.37; mol. wt. 176. Found: C, 88.03; H, 11.33; mol. wt. 167. Dimethyl-tert.-butyl~arbinol~~.-Between 60" and 104" (20 mm.), a considerable fraction came over which gave positive tests for unsaturation and chloride. The condensation product, 2,3,3-trimethyl-2-phenylbutanewas formed in the smallest yield (7%) of any of the isomers. It came over a t 105-108" (20 mm.), and was purified with difficulty. Anal. Calc'd for C12HZ0: C, 88.63; H, 11.37; mol. wt., 176. Found: C, 88.34; H, 11.47; mol. wt., 169. Mefhylethyl-n-propylc~rbinol~~.-Asmall amount (3 9.) of 2-chloro-2-ethylpentane18 was isolated from the low-boiling unsaturated fraction; b. p. 41" (20 mm.); n:, 1.4283. This was also prepared from the carbinol and hydrochloric acid. 2-Ethyl-2-phenylpentane was produced in 40% yield; b.p. 100" (15 mm.); 106107" (20 mm.); n:, 1.4964; n t , 1.4985. Since these constants do not agree with those given in the literature19 the compound was analyzed. Anal. Calc'd for C13H20: C, 88.63; H, 11.37. Found: C, 88.23; H, 11.44. Mefhylethylisopropylcarbinol20.-A 14% yield of 3-chloro-2,3-dimethylpentane21 was isolated from the low-boiling fraction; b. p. 41-42" (20 mm.). A 22% yield of 2,3-dimethyl-2-phenylpentane came over a t 105-107' (20 mm.). Anal. Calc'd for C13HZO: C, 88.63; H, 11.37; mol. wt., 176. Found: C, 88.26; H, 11.42; mol. wt., 166. TrimethylcarbinoP.-A small amount of 3-chloro-3-ethy1pentanez3 (2%) was recovered; b.p. 43-44' (20 mm.); n:, 1.4320. The condensation product, 3-ethyl-3-phenylpentane, came over a t 107-108" (20 mm.). I t boiled a t 225-226" (745 mm.); n:, 1.4975; n:, 1.4953. These constants do not agree with those given by SchreineP. The yield was 40%. Anal. Calc'd for C13H20: C, 88.63; H, 11.37. Found: C, 88.37; H, 11.41. SCHREINER, J . prakt. Chent., [2], 82, 294 (1910). SCHREINER, ibid., [2], 82, 294 (1910). 17 WHITMOREAND BADERTSCHER, J. Am. Chem. SOC.,66, 1559 (1933). 18 SCHREINER, J. prakt. Chem., [2], 82, 296 (1910). 19 HALSE,ibid., [2], 89, 452 (1914). 20 WHITMORE AND EVERS, J . Am. Chem. SOC.,66,812 (1933). 21 KASCHIRSKY, J. Russ. Phys.-Chem. SOC.,13, 90 (1883). 22 &TOYER AND hfARVEL, Organic Synthesis, VOl. XI, p. 98. 23 SCHREINER, J . prakt. Chem., [2], 82, 296 (1910).
'1
l6
254
R. C. HUSTON,
W. B. FOX, AND M. N.
BINDER
TABLE I BOILINGPOINTS,DENSITIESAND MOLECULAR VOLUMES VM YIELD
B.P.
Calo'd
Found
168-170 " 740 mm.
,8659
155.68
154.87
70
189-191 O 740 mm.
.8720
171.95
169.88
60
205-206" 745 mm.
.8718
188.22
185.97
55
209-210" 745 mm.
.8814
188.22
183.95
35
205-206 O 745 mm.
.8778
188.22
184.71
40
223.5-224.5' 745.6 mm. 107-107.5" 20 mm.
.8737
204.49
201.44
45
216-217" 745.7 mm. 101-102" 20 mm.
.8724
204.49
201.74
30
222-223" 745 mm. 105-107" 20 mm.
.8801
204.49
199.97
20
224-226" 746 mm. 107-108" 20 mm.
.8867
204.49
198.78
7
%
255
TERTIARY ALIPHATIC ALCOHOLS AND BENZENE
TABLE I-Concluded VM B.P.
YIELD
Calc'd
Found
224-226" 745.6 mm. 106-107" 20 mm.
.8786
204.49
200.32
40
224-226' 745 mm. 105-107" 20 mm.
.8803
204.49
199.93
22
225-226" 745.6 mm. 107:5O 20 mm.
.a807
204.49
199.83
40
%
DISCUSSION
A comparison of yields of condensation products obtained from the isomeric tert.-hexyl and heptyl alcohols would seem to indicate that the accumulation of alkyl groups on the carbon atom adjacent to the carbinol carbon has a marked depressing influence on the condensing capability of the compound. The same structural character appears to favor the formation of unsaturated compounds and te&-alkyl chlorides. Boiling points, densities and molecular volumes.-These constants were accurately determined and are assembled in Table I. The molecular volumes are calculated by the formulae developed by KauffmanZ4for unbranched homologues of benzene. I n the n-alkyldimethylphenylmethanes, the difference between calculated and observed values may be taken as the effect of the accumulation of two methyl groups on the carbon atom adjacent to a ring carbon, which is also an accumulation center. This effect appears to increase slightly as the length of the normal chain increases. A comparison of the molecular volumes of the isomeric propyldimethylphenylmethanes and the butyldimethylphenylmethanes gives a clear-cut picture of the effect of accumulation of radicals on adjacent and on nonadjacent carbons. These same groups show the highest boiling points in the compounds of greatest density and the lowest boiling points in the compounds having 2 4 KAUFFMAN, "Beziehungen zwischen physikalischen Eigenschaften und chemisher Konstitution," Verlag F. Enke, Stuttgart, Germany, 1920, p. 98.
256
R. C. HUSTON, W. B. FOX, AND M. N. BINDER
TABLE I1 SURFACE TENSIONS AND PARACHORS SURFACE TENSION BUB0TANCE
PARACHOR
Drop-wt.
DuNouy Tenaiometer
Calc'd
Drop-wt.
DuNouy Tensiometer
28.04
28.52
356.4
.356.4
357.9
28.88
29.73
396.4
393.9
396.6
28.95
30.54
436.4
431.4
437.1
29.59
31.82
436.4
429.
436.8
29.30
31.16
436.4
429.7
436.4
29.45
31.52
476.4
469.36
476.5
28.63
30.80
473.4
466.6
475.3
29.26
31.52
473.4
465.2
473.2
31.84
470.4
CHs
I
CHI-C-CeHs I
I
471.9
257
TERTIARY ALIPHATIC ALCOHOLS AND BENZENE
TABLE 11-Concluded BURFACB TENSION BURBTANCE
PARACEOR
DuNouy Tensiometer
DuNouy Tensiometer
Calc'd
29.60
31.93
476.4
466.6
476.1
29.47
31.83
473.4
465.8
474.8
29.66
32.13
476.4
464.0
475.8
Drop-wt.
Drop-wt.
___.
the smallest density. This relationship between density and boiling point is not clear-cut in the other isomers. Surface tension and parachor.-Surface tension was determined by the drop-weight method of Harkins, and by means of the DuNouy tensiometer, both a t 20". In calculating parachors, the constants of Mumford and Phillips2swere used, together with the suggested decrement of -3.0 for branched groups of the type - CHRz and double this value for the group - CR,. In addition a decrement of -3.0 was used for the attachment of the alkyl group on the benzene ring. The agreement between the calculated values and those determined by means of the tensiometer are very close. The greatest deviation is found in the case of 2 ,4-dimethyl-2-phenylpentane, in which case the density is relatively low. It is noteworthy that, although this compound has a higher V , than 2-methyl-2-phenylhexane, its parachor is slightly lower. Index of refraction and molecular refraction.-Indices of refraction were determined by the Abbe refractometer. Molecular refractions were calculated from the Lorentz-Lorenz formula. To eliminate any doubt as to the correctness of the formulae assigned to the tert.-alkylbenzenes attention is called to the following: ( a ) All alcohols were prepared by standard methods and were checked as to properties with the literature. ( b ) I n the rearrangement of alkyl groups during processes of condensa26
MUMFORD AND PHILLIPS, J . Chem. Soc., 33, 2112 (1929).
258
R. C. HUSTON, W. B. FOX, AND M. N. BINDER
TABLE I11 INDICESOF REFRACTION AND MOLECULAR REFRACTIONS Cala'd
Found
1.4923
44.79
44.94
1.4924
49.40
49.29
1,4934
54.02
54.02
1.4988
54.02
54.00
1.4955
54.02
53.99
1.4943
58.65
58.68
1.4928
58.65
58.67
1.4966
58.65
58.48
1.5019
58.65
58.62
259
TERTIARY ALIPHATIC ALCOHOLS AND BENZENE
TABLE 111-Concluded MR; 8UBUTANCB
Calo'd
Found
1.4964
58.65
58.53
1.4974
58.65
58.54
1.4975
58.65
58.53
CHs
\
CzHs-C-CsHs
/
CsH7 CHs
CHs
tion, primary groups may change to secondary or tertiary, and secondary groups may change to tertiary26. We were unable to find instances of the reverse processes in which appreciable yields of primary or secondary groups are formed from groups of higher branching. It was found that isobutyl alcohol does not condense with benzene in the presence of aluminum chloride at room temperature; above 50°, it reacts to form tert.-butylbenzenez7. ( c ) The properties of tert.-butyl- and tert.-amylbenzenes agree with those recorded in the literatures$7, The three possible tert.-hexylbenzenes were prepared, two of which have been prepared by other methods*, 11, All seven possible tert.-heptylbenzenes were prepared, three of which are recorded16 * 24. (d) Differences in the physical properties of the isomeric tert.-alkylbenzenes, as recorded in the tables are in accord with accepted rules. (e) All tert.-alkylbenzenes listed have been used in the preparation of p-tert.-alkylphenols of different and characteristic properties4 28. 9
26 KONOWALOW, J . Russ. Phys.-Chem. SOC.,27, 457 (1896); ESTREICHER, Ber., 33, 439 (1900); SCHRAMM, Monatsh., 9, 613, 615 (1888);GROSSIN,Bull. SOC. chim., [2], 41,446 (1884);VERLEY,ibid., [3],19, 72 (1898);MEYERAND BERNHAUER, Monatsh., 63,721 (1929);GILMAN AND CALLOWAY, J . Am. Chem. SOC.,66,4197(1933);LAUGHLIN, ibid., 66, 1395 (1934); IPATIEFF,PINES,AND SCHMERLING, NASH,AND WHITEMORE, ibid., 60, 353, (1938), etc. 27 TCHITCHIBABINE, Bull. soc. chim., [5e],2, 498 (1935). 2 8 HUSTON AND HEDRICK, J . Am. Chem. SOC.,69, 2001 (1937).
260
R. C. HUSTON, W. B. FOX, AND M . N. BINDER
Attempts to prepare the alkylbenzenes by the Wurtz-Fittig method gave only diphenyl and dialkyl. Part,ial oxidation of the tert.-alkyl side-chains did not yield information helpful in the determination of structure. SUMMARY
1. Tertiary aliphatic alcohols up to and including the isomeric heptyl alcohols were condensed with benzene by means of aluminum chloride to form tert.-alkylbenzenes. 2. The straight-chain carbinols, such as dimethyl-n-butylcarbinol, methylethyl-n-propylcarbinol and triethylcarbinol, condense readily to give good yields of t,he corresponding hydrocarbons. 3. Branched-chain carbinols, especially those in which branching occurs on the carbon adjacent to the carbinol carbon, condense much less readily. In these compounds there is a greater tendency to form unsaturated compounds and tert.-alkyl chlorides. 4. Boiling points, densities, indices of refraction, and surface tensions were determined. Molecular volumes, molecular refractions, and parachors were calculated.
