[CONTRIBUTION FROM
THE
NOYES CHEMICAL LABORATORY, UNIVERSITY OF ILLINOIS]
T H E DIALKYLATION OF NAPHTHALENE. 1, 4-DICYCLOHEXYLNAPHTHALENE CHARLES C. PRICE, HENRY M. SHAFER, MITCHELL F. HUBER, CARL BERNSTEIN
AND
Received July iY, i9.@
Although many dialkylated derivatives of naphthalene have been reported from Friedel-Crafts type alkylations, many of the products have not been separated into pure chemical components, and even for those few dialkylnaphthalenes which have been isolated as pure crystalline compounds, the structure has in no case been established. The dialkylnaphthalenes most readily obtained in crystalline form are t,he di-t-butyl derivatives (1, 2). Fractional distillation of the product from the reaction of naphthalene with 2-butyl or isobutyl chloride and aluminum chloride (1, 2) or with 2-butyl alcohol and boron fluoride (3) or hydrogen fluoride (4, 5)' gave solid mixtures of di-t-butylnaphthalenes. This mixture contained varying proportions of an isomer (I) which crystallized as stout, flat needles melting a t 145-146', and which could be converted to the corresponding quinone by chromic oxide in acetic acid (2), but could not be converted into a picrate. The residue remaining after separation of this high-melting isomer gave a beautifully crystalline picrate, m.p. 156-156.5'. This picrate, which was not previously analyzed successfully (2), has now been shown to be composed of three moles of hydrocarbon and two of picric acid. Furthermore, the hydrocarbon recovered from the purified picrate, which crystallized from alcohol as fine, cottony needles melting unsharply a t 80-82", has been shown to be a mixture of two isomers. Careful fractional recrystallization from alcohol or acetic acid yielded fine needles (11) melting sharply a t 103-104". A mixture of this substance (2 parts) with the higher-melting isomer (I) (1 part) melted a t 80-82' and was identical with the material recovered from the picrate. Evidently the picrate contains one molecule of I, two molecules of I1 and two of picric acid. CioHe(C4H& m.p. 146" L-
I
+ 2CioH6(C4&)2 m.p. 104' I1
A
m.p. 80-82'
2C~H3Ns07
4
NH40H
'
Picrate (3C1dh 4- 2C6H3H3o7) m.p. 156-156.5'
All attempts to establish the structure of these two hydrocarbons by degradation have failed. Oxidation with dilute nitric acid gave no naphthalic acids. Oxidation of either isomer I or I1 with mercuric sulfate and sulfuric acid yielded Tsukervanik and Terent'eva (5), using t-butyl alcohol and aluminum chloride, report a di-t-butylnaphthalene, m.p. 132", picrate, m.p. 99", which differs from any product isolated by any other procedure. 517
518
PRICE, SHAFER, HUBER, AND BERXSTEIN
small amounts of phthalic anhydride. This evidence may not signify the presence of both alkyl groups in one ring, however, since the sulfuric acid may have catalyzed the elimination of a t-butyl group during the oxidation (6). A synthetic approach also failed, since the reaction of p-di-t-butylbenzene with succinic or maleic anhydrides was found to result in almost complete elimination of one t-butyl group, the principal product from the two reactions consisting principally of p-t-butylbenzoylpropionic and acrylic acids, respectively.
co / \ CHz
(CHJ)~C\J /-\C(CH~)J -
+[
CH,
\ / co
\ 0- A'CIL (CHd /
0
#A,=---
$XX32CH,COOH
A similar elimination of a t-butyl group of p-di-t-butylbenzene has been previously observed for acetylation by Koch and Steinbrink ( 7 ) . From the alkylation of naphthalene with cyclohexanol and aluminum chloride, Bodroux (8) obtained a crystalline dicyclohexylnaphthalene, m.p. 151",as well as a liquid isomer. Using cyclohexene as the alkylating agent, Pokrovskaya and Stepantseva (9) obtained similar products. The crystalline isomer was dehydrogenated to a diphenylnaphthalene (9), m.p. 230', melting much higher than any previously reported diphenylnaphthalene. By alkylation of naphthalene with cyclohexanol and boron fluoride, we have obtained a new crystalline dicyclohexylnaphthalene, m.p. 83", accompanied by an isomeric liquid. Dehydrogenation of the new crystalline isomer by heating with selenium gave 1,4-diphenyInaphthalene,m.p. 132-133", identical with an authentic specimen. Similar dehydrogenation of the liquid material yielded only traces of a crystalline product, which melted at 231' and is evidently identical with the diphenylnaphthalene of unknown structure obtained by Pokrovskaya and Stepantseva (9). It was undoubtedly formed from traces of the high-melting (151') isomer present in the liquid in amounts too small to isolate. It thus appears that the alkylation of naphthalene with cyclohexanol yields at least three isomeric dicyclohexylnaphthalenes. The crystalline isomer melting at 83', isolated from the boron fluoride-catalyzed reaction, has been definitely identified as 1 ,4-dicyclohexylnaphthalene. The most likely structure for the crystalline isomer melting at 151' is that of 2,6-dicyclohexylnaphthalene. The liquid material is an isomer (or isomers) as yet unidentified.
EXPERIMENTAL^ E-t-butylnaphthulenes. The reaction of naphthalene (118 g.) with two moles of t-butyl chloride in 100 cc. of carbon disulfide proceeded vigorously on the addition of 8 g. of alu2
Analyses by Charles W. Beazley, L. G. Fauble, Mary Kreger, and Margaret McCarthy.
DIALKYLATION OF NAPHTHALENE
519
minum chloride with stirring. Hydrolysis and distillation yielded a solid mixture of di-tbutylnaphthalenes (88-95%), boiling a t about 200" (20 mm.). Approximately 10% of this mixture could be obtained as stout, flat needles by careful fractional recrystallization from methyl or ethyl alcohol, m.p. 145-146". The residue formed fine, cottony needles melting unsharply a t about 80-82". This latter material formed a picrate crystallizing from alcohol as lustrous, orange needles, m.p. 156-156.5", for which the analytical data indicate the formula (C,sHz4),(CeHsOlNa)z. Anal. Calc'd for CsaH~sNsOtr:C, 67.18; H, 6.67; N, 7.13. Found: C,67.09; H, 6.71; N, 7.20. Decomposition of the picrate regenerated the hydrocarbon as fine needles, m.p. 80-82". Careful recrystallization of this substance from acetic acid or alcohol yielded needles melting sharply a t 103-104". A mixture of this compound (2 parts) and the higher-melting isomer (1 part) melted a t 80-82" and was identical with the material recovered from the picrate. The higher-melting isomer was readily converted to the corresponding quinone, m.p. 8343.5" (2), but all attempts to prepare a quinone from the lower-melting isomer or the low-melting mixture by oxidation with chromic acid in acetic acid have yielded red oils from which no crystalline material could be isolated. Reductive acetylation of the oily oxidation product by heating with zinc dust in acetic anhydride gave an oil from which a small amount of white needles, m.p. 139-140°, was obtained by recrystallization from alcohol. These needles are evidently the diacetate of the hydroquinone derived from the high-melting hydrocarbon. Anal. Calc'd for CzzHZ8Oa: C, 74.13; H, 7.92. Found: C, 73.76, 74.44; H, 7.78, 8.00. Oxidation of either di-t-butylnaphthalene with mercuric sulfate in concentrated sulfuric acid yielded only phthalic acid. Either the t-butyl groups are on the same ring or, very probably, the sulfuric acid caused dealkylation ( 6 ) . p-Di-t-butylbenzene and succinic anhydride in carbon disulfide solution were treated with an equivalent amount of aluminum chloride at -15" for twelve hours. Hydrolysis, followed by extraction with sodium bicarbonate yielded a large amount of acid. This material was almost entirely p-t-butylbenzoylpropionic acid, m.p. 126" (2), identified further by permanganate oxidation to p-t-butylbenzoic acid, m.p. 162" (2). By careful fractional crystallization from methanol, a small portion (3.5%) of the crude product was isolated as colorless tetragonal crystals, m.p. 176-177". This acid was isolated more readily by converting the crude acid mixture to its benzylthiuronium salt with a limited quantity of benzylthiuronium chloride (10). The salt, m.p. 142-143", was decomposed by dissolving in hot acetic acid; the free acid crystallized on cooling. This acid had the proper neutral equivalent for a di-t-butylbenzoylpropionic acid but the analysis indicated two too few hydrogen atoms. The product gave a negative test for unsaturation with bromine and with permanganate. Anal. Calc'd for ClsH~aOa:C , 74.43; H, 9.03; N.E., 290. Calc'd for C18H2408: C, 74.95; H, 8.39; N. E., 288. Found: C, 74.96; 74.98, 75.03; H, 8.29, 8.30, 8.58; N. E., 286, 284, 288. Oxidation with permanganate (11) has yielded two crystalline oxidation products. One, lustrous pearly plates, m.p. 194-196", is apparently the normal oxidation product, since the analysis and neutral equivalent indicated a product with two less hydrogen atoms than di-2-butylbenzoic acid. Anal. Calc'd for CISH2202: C, 76.88; H, 9.47; N. E., 234. Calc'd for C1SH2002: C, 77.55; H, 8.68; N. E., 232. Found: C, 77.53; H, 8.69; N. E., 231. A second oxidation product, m.p. 217-218', had the same neutral equivalent (233) but contained 71.41% carbon and 7.33% hydrogen. p-Di-t-butylbenzene and maleic anhydride were condensed by the same procedure as that used for succinic anhydride. The only product which could be isolated was p-t-butyl-
520
PRICE, SHAFER, HUBER, AND BERNSTEIN
benzoylacrylic acid, which crystallized from benzene-ligroin as yellow-green plates, m.p. 123", or yellow-green needles, m.p. 128". Anal. Calc'd for CI4HlsOa:C, 72.38; H, 6.93; X. E., 232. Found (123"): C, 72.44; H, 7.09; N. E., 231. Found (128'): C, 72.21; H, 7.06; Tu'. E., 233. Both forms gave positive tests for unsaturation with bromine and with permanganate, and yielded p-t-butylbenzoic acid on oxidation. Dicyclohexylnaphthalene. Boron fluoride was found to be a much more convenient catalyst for alkylation of naphthalene with alcohols (3) than aluminum chloride. The reaction is carried out very simply b y passing boron fluoride through a suspension of naphthalene in alcohol at room temperature. I n several reactions cooled to 0" there was no apparent reaction for half a n hour or so and then the reaction proceeded so vigorously that all stoppers were blown out of the apparatus and a considerable portion of the reaction mixture was lost. Apparently, when the alkylation mixture is cooled, the boron fluoride dissolves without reacting and then suddenly, all the dissolved catalyst reacts at once, whereas, at room temperature, the reaction proceeds smoothly as the boron fluoride is passed into the mixture. To prepare dicyclohexylnaphthalenes, 128 g. (1 mole) of naphthalene was suspended in 220 g. (2.1 moles) of cyclohexanol in a 1-liter flask. Boron fluoride was passed in rapidly for thirty minutes; the mixture was allowed to warm up from the heat of reaction. The dark red reaction mixture separated into two layers and, after standing for one day a t room temperature, i t was washed with dilute alkali and water; 300 cc. of benzene was added to facilitate the washing process. The pale tan benzene solution was dried and distilled. The dicyclohexylnaphthalene fraction, 55 g. (19%), b.p. 240-260" (6 mm.), was a pale yellow oil. The oil was dissolved in the minimum amount of ligroin and cooled in a solid carbon dioxide-alcohol bath to induce crystallization. After three weeks a t O", 7 g. of crystalline material had separated. Recrystallization from ligroin and from alcohol yielded 1,Q-dicyclohexylnaphthalene,m.p. 8343.5". Anal. Calc'd for C22H28: C, 90.35; H, 9.65. Found: C, 90.15; H, 9.61. Dehydrogenation. The position of the dicyclohexyl groups was demonstrated by dehydrogenation of 7 g. of the hydrocarbon with 14 g. of selenium a t 350" for sixty hours. Distillation of the product, followed by recrystallization from alcohol, gave a substantial yield of 1 ,$-diphenylnaphthalene, clusters of needles, m.p. 132-133". The identity was checked by a mixed melting point determination with an authentic specimen. The liquid dicyclohexylnaphthalene mixture recovered from the first crystallization of the 1,4-isomer was subjected to the same treatment with selenium. Only a minute amount of diphenylnaphthalene was recovered; i t crystallized from alcohol as shiny plates, m.p. 231". It is evidently identical with the diphenylnaphthalene Pokrovskaya and Stepantseva (9) obtained by dehydrogenation of the dicyclohexylnaphthalene melting at 151'. I n view of the high melting point of these two compounds, in comparison with isomers of known structure, i t seems highly probable that the phenyl and cyclohexyl groups are in the 2,6-position. SUMMARY
A new di-t-butylnaphthalene, m.p. 104', has been isolated from the mixture formed by the alkylation of naphthalene. The dialkylated material melting a t about 80-82' has been shown to be a mixture of two parts of this new isomer and one part of the isomer melting a t 146'. These two isomers form a mixed picrate composed of one mole of the high-melting (146') di-t-butylnaphthalene, two of the low-melting (104') isomer and two of picric acid. The principal product of the reaction of p-di-t-butylbenzene with succinic
DIALKYLATION OF NAPHTHALENE
521
anhydride was p-t-butylbenzoylpropionic acid, accompanied by small amounts of a saturated acid of unknown structure containing two less hydrogen atoms than di-t-butylbenzoylpropionic acid. From the boron fluoride-catalyzed alkylation of naphthalene with cyclohexan01 a new crystalline dicyclohexylnaphthalene, m.p. 83-83.5’, has been isolated. Since dehydrogenation yielded 1,4-diphenylnaphthalene, this compound must be 1,4-dicyclohexylnaphthalene. URBANA,ILL. REFERENCES
(1) GUMP,J. Am. Chem. SOC.,63, 380 (1931). (2) FIESERAND PRICE, J. Am. Chem. SOC.,68, 1838 (1936). (3) PRICEAND CISKOWSKI, J.Am. Chem. SOC.,60,2499 (1938). TINKER, AND WEINMAYR, J. Am. Chem. SOC.,61, 1013 (1939). (4) CALCOTT, (5) TSUKERV-4NIK AND TERENT’EVA, J. Gen. Chem. (U.S.S.R), 7, 637 (1937). (6) IPATIEFF AND CORSON, J. Am. Chem. SOC.,69, 1417 (1937). Brennstof-chem., 19, 277 (1938). (7) KOCHAND STEINBRINK, (8) BODROUX, Ann. Chim., (10)11, 511 (1929). AND STEPANTSEVA, J. Gen. Chem. (U.S.S.R.), 9, 1953 (1939). (9) POKROVSKAYA (10) DONLEAVY, J. Am. Chem. SOC.,68,1004 (1936). (11) SRRINERAND FUSON, “The Systematic Identification of Organic Compounds,” John Wiley and Sons, Inc., New York, 1940, p. 164.
