t-Butyl Chloride-Aluminum Chloride1

t-BuCl.AlCl3
(t-BuCl)

[507-20-0]  · C4H9Cl  · t-Butyl Chloride-Aluminum Chloride  · (MW 92.57) (AlCl3)

[7446-70-0]  · AlCl3  · t-Butyl Chloride-Aluminum Chloride  · (MW 133.34)

(t-butylating agent;1 hydrocarbon isomerization promoter;1 sludge AlCl3 catalyst3)

Physical Data: t-BuCl: bp 51-52 °C; AlCl3: sublimes at 178 °C.

Solubility: both t-BuCl and AlCl3 sol organic solvents such as CH2Cl2 and CHCl3 as well as CS2.

Form Supplied in: t-BuCl: liquid; AlCl3: solid. Both are commercially available.

Preparative Method: prepared by mixing equimolar amounts of t-BuCl and AlCl3 at -78 °C.2 This compound is a white or pale yellow needle-like crystal, which is stable and can be stored indefinitely at -78 °C. However, it decomposes at about -30 °C to yield a reddish liquid and HCl. In most reactions involving the use of t-BuCl.AlCl3, both t-BuCl and AlCl3 are generally added to the reaction solution independently without premixing. The ratio between t-BuCl and AlCl3 may also vary, depending on the requirement of the specific reaction.

Handling, Storage, and Precautions: t-butyl chloride-aluminum chloride is corrosive and moisture sensitive. Thus it should be handled in an anhydrous atmosphere.

Introduction.

t-Butyl chloride-Aluminum Chloride (1:1 molar ratio) is prepared at -78 °C, but is not stable at -30 °C and decomposes into a reddish liquid,2 which belongs to a family of catalysts called aluminum chloride sludges.3 The sludges are valuable catalysts for commercial-scale alkylation reactions since the liquid state of the catalysts ensures continuous flow operations.3 Sludge catalysts have also found application in hydrocarbon isomerization.3,27 Reagents derived from t-BuCl.AlCl3 are not limited to the 1:1 molar ratio of the components. In many reactions, varying ratios of t-BuCl and AlCl3 may be used, depending on the need of the specific reaction, and the addition of t-BuCl and AlCl3 is generally performed without premixing the two components.

t-Butylation.

t-Butyl chloride-aluminum chloride is primarily used as a t-butylating agent in organic synthesis.1 Efforts have been made to determine the structure and nature of this reagent. 1H NMR analysis showed that the crystalline compound, isolated from the reaction of 1:1 molar equivalent of t-BuCl and AlCl3 at -78 °C, is only a donor-acceptor complex since the complex did not contain any free t-butyl cation. However, t-BuCl was completely ionized to Me3C+Al2Cl7- in anhydrous HCl with excess AlCl3 (eq 1).4

Friedel-Crafts alkylation with t-BuCl.AlCl3 as a t-butylating agent has been well studied.1 Early interest in this reaction was directed toward the mechanism of ionization.1,5 The practical importance of the t-butylation in the perfume industry for the preparation of xylene musk also provided further impetus for examination.1a Recently, this reaction has been employed in organic synthesis to protect certain positions of arenes.6 The t-butyl group introduced can be readily removed later.7 Two important features have been established regarding the use of t-BuCl.AlCl3 as an alkylating agent in aromatic substitution.1a It is difficult to achieve ortho substitution of substituted aromatic compounds, with the exception of fluorine substituted compounds. This is due to the steric bulk of the t-butyl group. Further, due to the strong Lewis acidic character of AlCl3, t-butylation of aromatic compounds using t-BuCl.AlCl3 is always accompanied by isomerization and disproportionation. These side reactions can be suppressed by employing solvents such as MeNO2 and varying the reaction conditions.

Various arenes have been alkylated by t-BuCl.AlCl3 (eq 2). The reaction occurs readily with benzene, monosubstituted benzene (alkyl and halo), o-xylene, and m-xylene as substrates.1,8 However, abnormal reactions were encountered when arenes such as p-xylene and p-chlorotoluene are used as substrates, which only have ortho positions available for the intended t-butylation.9 For example, the principal products from the reaction of p-xylene with t-BuCl.AlCl3 are isobutane, toluene, m- and p-t-butyltoluenes, 3,5-di-t-butyltoluene, 2-(p-methylbenzyl)-p-xylene, and di-p-xylylmethane (eq 3).9a,9b With an excess of t-BuCl, 1,3,5-tri-t-butylbenzene can be prepared from di-t-butylbenzene in good yield (eq 4).10 The t-BuCl.AlCl3 system is able to alkylate phenols, but the best results with these substrates were obtained by use of alkenes and alcohols as alkylating agents.1a t-Butylation of naphthalene and its derivatives is also successfully achieved with t-BuCl.AlCl3.11 In the case of naphthalene, only the thermodynamic product, 2-t-butylnaphthalene, is observed (eq 5).1a When acenaphthene is used in the alkylation, both mono- and disubstitution products are obtained (eq 6).12

t-Butyl chloride-aluminum chloride has also been used for the t-butylation of alkenic substrates. Its reaction with alkenes was widely studied due to its obvious industrial importance.13,14 Although oligomerization of alkenes can occur,13e it is possible to obtain b-t-butylalkyl chlorides as the major addition products of the reaction (eq 7).14a-d Elimination of HCl in situ led to the formation of t-butylated alkenes.13a,14 Silyl enol ethers react with t-BuCl.AlCl3 to yield a-t-butyl ketones or aldehydes (eq 8).15 However, the best Lewis acid for this type of reaction is Titanium(IV) Chloride. Compounds which contain very acidic C-H bonds, such as malononitrile, can be similarly t-butylated, presumably through enolization.16

Silylalkynes react with t-BuCl.AlCl3 to form t-butylated alkynes (eq 9).17

t-Butyl chloride-aluminum chloride has been used to t-butylate PCl3.18 When PCl3 is treated with t-BuCl.AlCl3, t-butylphosphonyl dichloride is obtained upon hydrolysis (eq 10) (Clay reaction). This reaction is also applicable to a number of organophosphorus compounds such as dichlorophenylphosphine (eq 11) and chlorodiphenylphosphine.19 Reaction with diphosphorus pentasulfide leads to the formation of t-butylphosphinothioic acids after hydrolysis.20

Reaction between t-BuCl.AlCl3 and chloroamines was also investigated.21 When trichloroamine is used, 90% t-butylamine is obtained, along with 8% of 2,2-dimethylaziridine as a minor product (eq 12). However, the use of monochloroamine decreased the yield of t-butylamine to a range of only 7-20%.

Hydride Abstraction and Isomerization.

When t-BuCl.AlCl3 reacts with crowded arenes such as p-xylene, abnormal reactions occur.9 This results from initial hydride abstraction by t-BuCl.AlCl3 from the benzylic positions. Similar reactions are observed with p-chlorotoluene and other crowded aromatics. When the t-butylation is conducted in the presence of an isoalkane, not only t-butylated products but also the alkylarenes derived from the isoalkane are observed (eq 13).22 This phenomenon can also be explained by hydride abstraction by t-BuCl.AlCl3 from the alkanes. This hydride abstraction has been elegantly utilized in the preparation of polyalkyltetralins (intermediates in the manufacture of musk aroma compounds, eq 14).23 The polyalkyltetralins are prepared by combining p-cymene with alkenes under the catalysis of t-BuCl.AlCl3. The reaction goes through initial hydride abstraction by t-BuCl.AlCl3 from the p-cymene to generate the cumyl cation, which is subsequently alkylated by an alkene. A concurrent cyclization yields the final product.23 1,1,4,4,5,5,8,8-octamethyl-1,2,3,4,5,6,7,8-octahydroanthracene can be prepared by combining 1,3,5-tri-t-butylbenzene with t-BuCl.AlCl3 (eq 15).24

t-Butyl chloride-aluminum chloride is exploited in the preparation of diamondoid compounds.25 It was found that t-BuCl facilitates the isomerization of trimethylenenorbornane to adamantane by AlCl3 (eq 16). The same reagent is also employed in the isomerization of heptacyclo[8.4.0.02,12.03,8.04,6.05,9.011,13]tetradecane (binor-S).26 Compared to the t-BuBr.AlBr3 system, t-BuCl.AlCl3 is less well documented in the literature for this type of isomerization.27

t-Butyl chloride-aluminum chloride is also found to facilitate the methylation of methylcyclohexane with tetramethylsilane (eq 17).28 Only 5% 1,1-dimethylcyclohexane is obtained when methylcyclohexane was treated with Me4Si.AlCl3. In contrast, 85% 1,1-dimethylcyclohexane was obtained when t-BuCl was added to the reaction system.

Other Reactions.

t-Butyl chloride-aluminum chloride is a good chlorinating agent for isoalkanes. It has been successfully used to selectively chlorinate 2,3-dimethylbutane (eq 18) and methylcyclohexane at the tertiary positions in excellent yields.29 Dehydrochlorination of 2-chloro-2,3-dimethylbutane led to formation of 2,3-dimethylbutenes. When 1-chloro-1-methylcyclohexane was subjected to the same treatment, both 1-methylcyclohexene and methylenecyclohexane were obtained. The two reactions, along with recycling of HCl and isobutene, led to an industrial process for the manufacture of tertiary monoalkenes.29

t-Butyl chloride interacts with AlCl3 to eliminate HCl to form isobutene, which can be polyacetylated by Acetyl Chloride.30 Upon treatment of the reaction mixture with aqueous Ammonia, 2,4,6-trimethylpyridine, 4-acetonyl-2,6-dimethylpyridine, and 1,3,6,8-tetramethyl-2,7-naphthyridine were obtained in total 92% yield with a ratio of 36:40:24, respectively. If liquid ammonia is used, the yield of the reaction remained the same, but the proportion of 1,3,6,8-tetramethyl-2,7-naphthyridine increased to 63%, while only traces of 4-acetonyl-2,6-dimethylpyridine could be detected. The amount of 2,4,6-trimethylpyridine obtained was essentially the same (eq 19).


1. (a) Roberts, R. M.; Khalaf, A. A. Friedel-Crafts Alkylation Chemistry; Dekker: New York, 1984. (b) Olah, G. A. Friedel-Crafts Chemistry; Wiley: New York, 1973. (c) Thomas, C. A. Anhydrous Aluminum Chloride in Organic Chemistry; Reinhold: New York, 1941. (d) Price, C. C. OR 1946, 3, 1.
2. Cesca, S.; Priola, A.; Ferraris, G. Makromol. Chem. 1972, 156, 325.
3. Olah, G. A. In Friedel-Crafts and Related Reactions; Olah, G. A., Ed.; Interscience: New York, 1963; Vol. 1, Chapter 4.
4. Kalchschmid, F.; Mayer, E. AG 1976, 88, 849.
5. DeHaan, F. P.; Chan, W. H.; Chang, J.; Ferrara, D. M.; Wainschell, L. A. JOC 1986, 51, 1591.
6. (a) Tashiro, M.; Koya, K.; Yamato, T. JACS 1982, 104, 3707. (b) Tashiro, M.; Yamato, T. JOC 1979, 44, 3037. (c) Tashiro, M.; Yamato, T. JCS(P1) 1979, 176. (d) Tashiro, M.; Yoshiya, H.; Yamato, T. S 1978, 399. (e) Tashiro, M.; Yamato, T. S 1978, 214. (f) Tashiro, M.; Yamato, T.; Fukata, G. J. JOC 1978, 43, 1413. (g) Tashiro, M.; Fukata, G. J. JOC 1977, 42, 1208.
7. Olah, G. A.; Prakash, G. K. S.; Iyer, P. S.; Tashiro, M.; Yamato, T. JOC 1987, 52, 1881.
8. (a) Bartlett, P. D.; Roha, M.; Stiles, M. JACS 1954, 76, 2349. (b) Olah, G. A.; Flood, S. H.; Moffatt, M. E. JACS 1964, 86, 1060. (c) Olah, G. A.; Flood, S. H.; Moffatt, M. E. JACS 1964, 86, 1065.
9. (a) Friedman, B. S.; Morritz, F. L.; Morrissey, C. J.; Koncos, R. JACS 1958, 80, 5867. (b) Schmerling, L.; Luvisi, J. P.; Welch, R. W. JACS 1959, 81, 2718. (c) Roberts, R. M.; McGuire, S. M. JOC 1970, 35, 102.
10. (a) Watarai, S. BCJ 1963, 36, 747. (b) Myhre, P. C.; Rieger, T.; Stone, J. T. JOC 1966, 31, 3425.
11. (a) Brady, P. A.; Carnduff, J.; Leppard, D. G. TL 1972, 4183. (b) Buu-Hoi, N. P.; LeBihan, H.; Binon, F.; Ryet, P. JOC 1950, 15, 1060. (c) Ferris, R. T.; Hamer, D. JCS 1961, 1409. (d) Rieker, A.; Zeller, N.; Schurr, K.; Muller, E. LA 1966, 697, 1.
12. (a) Peters, A. T. Nature 1965, 205, 170. (b) Illingworth, E.; Peters, A. T. JCS 1952, 2730. (c) Illingworth, E.; Peters, A. T. JCS 1951, 1602. (d) Nursten, H. E.; Peters, A. T. JCS 1950, 729. (e) Peters, A. T. JCS 1947, 742.
13. (a) Soldatova, V. A.; Mekhtiev, S. D.; Sadykhov, S. G.; Sadykhova, F. N.; Brzhezitskaya, L. M. Neftekhimiya 1973, 13, 272. (b) Brandstrom, A. ACS 1959, 13, 963. (c) Schmerling, L. JACS 1947, 69, 1121. (d) Miller, V. A. JACS 1947, 69, 1764. (e) Kabas, G.; Gabler, R. JOC 1965, 30, 1248.
14. Ketslakh, M. M.; Rudkovskii, D. M.; Eppel, F. A. J. Appl. Chem. USSR 1959, 32, 2167.
15. (a) Chan, T. H.; Paterson, I.; Pinsonnault, J. TL 1977, 4183. (b) Reetz, M. T.; Maier, W. F.; Heimbach, H.; Giannis, A.; Anastassious, G. CB 1980, 113, 3734.
16. Boldt, P.; Militzer, H.; Thielecke, W.; Schulz, L. LA 1968, 718, 101.
17. (a) Capozzi, G.; Ottana, R.; Romeo, G.; Marcuzzi, F. G 1985, 115, 311. (b) Capozzi, G.; Romeo, G.; Marcuzzi, F. CC 1982, 959.
18. Clay, J. P. JOC 1951, 16, 892.
19. (a) Kaushik, M. P.; Vaidyanathaswamy, R. IJC(B) 1981, 20B, 932. (b) Petrov, K. A.; Chauzov, V. A.; Agafonov, S. V. JGU 1980, 50, 1227.
20. Murav'ev, I. V.; Fedorovich, I. S. JGU 1975, 45, 1711.
21. (a) Kovacic, P.; Lowery, M. K. JOC 1969, 34, 911. (b) Strand, J. W.; Kovacic, P. JACS 1973, 95, 2977.
22. Schmerling, L. JACS 1975, 79, 6134.
23. Frank, W. C.; Miller, D. M. BCJ 1993, 66, 125.
24. (a) Barclay, L. R. C.; Betts, E. E. JACS 1955, 77, 5735. (b) Barclay, L. R. C.; Betts, E. E. CJC 1955, 33, 672.
25. (a) Kuras, M.; Hala, S.; Landa, S. Sb. Vys. Sk. Chem.-Technol. Praz, Technol. Paliv 1971, 22, 95 (CA 1972, 76, 59 046s). (b) Kafka, Z. Sb. Vys. Sk. Chem.-Technol. Praz, D: Technol. Paliv 1991, D59, 79 (CA 1993, 118, 80 529x).
26. Kafka, Z.; Vodicka, L. CCC 1985, 50, 1212.
27. (a) McKervey, M. A.; Rooney, J. J. In Cage Hydrocarbons; Olah, G. A., Ed.; Wiley: New York, 1990; p 39. (b) Gund, T. M.; Williams, V. Z.; Osawa, E.; Schleyer, P. V. R. TL 1970, 3877.
28. Parnes, Z. N.; Bolestova, G. I.; Shevchenko, N. V.; Vol'pin, M. E. DOK 1991, 317, 406.
29. Vives, V. C.; Kruse, C. W.; Kleinschmidt, R. F. Ind. Eng. Chem., Process. Res. 1969, 8, 432.
30. (a) Erre, C. H.; Roussel, C. BSF(2) 1984, 449. (b) Erre, C.; Pedra, A.; Arnaud, M.; Roussel, C. TL 1984, 25, 515.

George A. Olah, G. K. Surya Prakash, Qi Wang & Xing-ya Li

University of Southern California, Los Angeles, CA, USA



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