Proceedings of the Tomsk Polytechnic Institute named after S. S. Kirov, holder of the Order of the October Revolution and the Order of the Red Banner of Labor

Volume 257                                                                                                                                1973

Research in the Chemistry of Carbazole Derivatives

81. Acetylation of Carbazole with Acetyl Chloride in Nitromethane

Yu. G. Yur’ev, V. L. Ivasenko, V. P. Lopatinskii

(Presented by the scientific-methodological seminar of the organic departments and laboratories of TPI)

Continuing our work on the investigation of the acetylation of carbazole [1, 2], we have studied the interaction of the latter with acetyl chloride and aluminum chloride in a nitromethane solution.

It is known that carbazole itself is substituted in positions 3 and 6, even when the amount of acetylating agent is less than equimolecular [3]. Later, however, it was shown that, depending on the nature and amount of the acetylating agent, the catalyst, and the reaction conditions, the main products formed are 9-acetylcarbazole [1, 4] or 3,6-diacetylcarbazole [2]. Under these conditions, 3-acetylcarbazole is obtained only in very small amounts [4].

In studying the rearrangement of 9-acetylcarbazole under the action of aluminum chloride into 1- and 3-acetylcarbazoles, we showed that the initial stage of isomerization is the cleavage of the acetyl group from position 9 and the formation of carbazole, which is then substituted to give C-acetylcarbazoles [5]. The presence of carbazole in the rearrangement product, as an intermediate product, made it possible to suppose that 3-acetylcarbazole could be obtained under the conditions of the rearrangement studied.

Indeed, as the data in the table show, at an equimolecular ratio of the starting reagents the principal product of the reaction is 3-acetylcarbazole, while the content of 3,6-diacetylcarbazole does not exceed 6–8% (see experiments 10–12). Noteworthy is the fact that at the initial moment of the reaction 9-acetylcarbazole is formed, the content of which rapidly decreases as the reaction duration increases. Moreover, with a decrease in temperature

the yield of 9-acetylcarbazole increases, while the content of 3-acetylcarbazole decreases.

When acetyl chloride and catalyst are increased to two moles per 1 mole of carbazole, the content of 3-acetylcarbazole increases only slightly (by 5–7%), whereas the yield of 3,6-diacetylcarbazole increases approximately fourfold (28–30% versus 6–8%). Increasing only the amount of acetyl chloride, on the other hand, increases the yield of 3-acetylcarbazole to a greater extent than that of 3,6-diacetylcarbazole. With an excess of catalyst up to two moles per 1 mole of carbazole, the yields of all reaction products decrease noticeably and they undergo strong resinification.

Thus, having studied the influence of the amounts of acetyl chloride and catalyst, the temperature, and the duration of the reaction on the yields of the products of carbazole acetylation, it may be proposed that under these conditions the reaction proceeds through the formation of 9-acetylcarbazole, which then undergoes the Fries rearrangement. The presence of 3,6-diacetylcarbazole is the result of secondary acetylation of the 3-acetylcarbazole formed.

Experimental Part

Starting reagents: nitromethane, “pure” grade, dried over phosphorus pentoxide and distilled; acetyl chloride, “pure” grade; aluminum chloride, freshly sublimed; carbazole, “pure” grade, recrystallized three times from xylene, with m.p. = 243°.

Acetylation of carbazole. Into a three-necked flask fitted with a reflux condenser with a calcium chloride tube, a stirrer, and a dropping funnel is placed a solution of 1.67 g (0.01 mole) of carbazole in 30 ml of nitromethane, and it is heated to the required temperature. With vigorous stirring, from the dropping funnel is added a solution of 0.72 ml (0.01 mole) of acetyl chloride and 1.33 g (0.01 mole) of aluminum chloride in 10 ml of nitromethane. The contents of the flask are heated under the conditions given in the table, poured into cold water, and the precipitate is filtered off, washed on the filter with water, and dried.

Chromatographic analysis. 100–200 mg of the reaction product is dissolved in a minimum amount of benzene and charged onto a chromatographic column (500 × 15) filled with activated KSK-grade silica gel of 250–500 μ particle size. Carbazole and a mixture of I- and 9-acetylcarbazoles are eluted with benzene; 3-acetyl-

Table I

Reaction conditions and yields of products of acetylation of carbazole

and 3,6-diacetylcarbazole, and with ethanol, the resin. After evaporation of the solvents, the yields of the individual components are determined by weighing. The accuracy of the analysis is 4%. 9-Acetylcarbazole is determined by saponification with an alcoholic alkali solution according to the procedure of [6].

References

1. V. P. Lopatinskii, E. E. Sirotkina, M. I. Sukhoroslova. Methods for Preparing Chemical Reagents and Preparations, issue II. Moscow, 28 (1964).

2. R. P. Lopatinskii, M. M. Anosova, L. P. Konkina. Izvestiya TPI, 136, 15 (1965).

3. S. Plant, R. Rogers, S. Williams. J. Chem. Soc., 1935, 741.

4. E. Funakuba, T. Genma, T. Takahashi, Technol. Repts. Osaka Univ., 12, 177 (1962).

5. Yu. G. Yur’ev, V. P. Lopatinskii, V. L. Ivasenko, I. S. Isaev, M. I. Gorfinkel, ZhOKh, 1971, in press.

6. Yu. P. Shakhirev. Candidate’s dissertation. Tomsk, 1965.