PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC
INSTITUTE named after S. M. KIROV

Vol. 136　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1965

RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

32. SYNTHESIS AND CERTAIN TRANSFORMATIONS OF 9-($\alpha$-ACETOXYETHYL)CARBAZOLE

V. P. LOPATINSKII, Yu. P. SHEKHIREV

The introduction of an ester group into the carbazole molecule is of great practical interest, since the products formed in this process may serve as starting materials for the synthesis of vinyl derivatives of carbazole. Usually the synthesis of esters in the carbazole series is carried out in two stages: first an alkoxy group is introduced into the carbazole molecule, and then it is esterified. Taking into account the ability of complex vinyl ethers to add various compounds at the double bond, we decided to carry out this synthesis in one stage by adding vinyl acetate to carbazole.

According to the literature, an analogous reaction was carried out between vinyl acetate and phthalimide on heating to 160–170°C in the presence of caustic potash [1] or without a catalyst [2]. In the latter work it was indicated that, under similar conditions, carbazole does not react with vinyl acetate.

Our investigations show that if the reaction of carbazole with vinyl acetate is carried out in acetone or methyl ethyl ketone solution in the presence of 5–10% (by weight of carbazole) of solid caustic potash or caustic soda, carbazole very readily reacts with vinyl acetate. Examination of the products formed established that under these conditions the reaction proceeds simultaneously in two directions: with formation of the product of addition of carbazole to vinyl acetate—9-($\alpha$-acetoxyethyl)carbazole—and with formation of an acetyl derivative of carbazole—9-acetylcarbazole.

The content of these two substances in the reaction products depends above all on the temperature conditions under which the process is carried out; moreover, it proved that in order to attain high yields of the addition product it is necessary to maintain the reaction temperature in the range 10–20°C below zero. Under these conditions it is possible to obtain a yield of 9-($\alpha$-acetoxyethyl)carbazole averaging about 80% of theory. As the temperature is raised, the yield of the acetyl derivative increases.

The 9-($\alpha$-acetoxyethyl)carbazole synthesized by us is an isomer of the 9-($\beta$-acetoxyethyl)carbazole described in the literature [3], but differs sharply from the latter in its chemical properties. Thus, on heating with water, aqueous solutions of acids and alkalis, it readily decomposes with formation of carbazole, acetaldehyde, and acetic acid, whereas its $\beta$-isomer is hydrolyzed only on heating with aqueous alkali solutions, to 9-($\beta$-oxyethyl)carbazole. Noticeable

decomposition of 9-(α-acetoxyethyl)carbazole also occurs when it is stored in air. We used the reaction of its decomposition by water in acetone solution on heating for the quantitative determination of this compound.

The acetyl group in the compound described possesses great mobility and can readily be replaced by other groups, for example an alkoxyl group. This replacement is easily effected by simply heating 9-(α-acetoxyethyl)carbazole with alcohols for 5–10 min. In this way we succeeded in obtaining a series of simple ethers of 9-(α-oxyethyl)carbazole in good yields. With an increase in the heating time, the resulting 9-(α-alkoxyethyl)carbazoles decompose to carbazole under the action of the acetic acid liberated as a result of the reaction. Therefore, for purification of 9-(α-acetoxyethyl)carbazole by recrystallization, solvents containing hydroxyl groups cannot be used. Under analogous conditions its β-isomer does not react with alcohols.

On distillation in vacuum, 9-(α-acetoxyethyl)carbazole decomposes with liberation of acetic acid, 9-vinylcarbazole, and carbazole; in our experiments the yield of the vinyl derivative did not exceed 37% of theory. According to literature data, decomposition of 9-(β-acetoxyethyl)carbazole occurs under much harsher conditions (500–600°C) and gives a yield of the vinyl derivative of 23% [3].

In the course of the present investigation we have also shown that various carbazole derivatives, for example 3-chloro- and 3-nitrocarbazoles, also enter into reaction with vinyl acetate, with formation of the corresponding 9-(α-acetoxyethyl)carbazoles, the properties of which are currently being studied.

Experimental Part

9-(α-Acetoxyethyl)carbazole. Into a three-necked flask equipped with a stirrer, thermometer, and dropping funnel are successively charged 10 g of carbazole, 0.5 g of finely powdered caustic potash, and 50 ml of acetone. The flask is placed in a cryostat at a temperature of 10–20°C below zero. When the indicated temperature has been reached in the reaction mass, 8.4 ml of freshly distilled vinyl acetate is added dropwise to the contents of the flask over 40 min. The carbazole gradually passes into solution. After all the vinyl acetate has been added, the reaction mixture is kept at the indicated temperature for another 20 min, then filtered from the catalyst and subjected to removal of the solvent. The remaining yellow oil is dissolved in petroleum ether. On cooling, 9-(α-acetoxyethyl)carbazole crystallizes from the solution, m.p. 85–87°C. Yield 12.8 g (84.3% of theory). For purification, the product is crystallized from a mixture of hexane and benzene (3:1). The product is very readily soluble in aromatic hydrocarbons, aliphatic ketones, and ether.

Methyl and ethyl ethers of 9-(α-oxyethyl)carbazole. To 13.5 g of 9-(α-acetoxyethyl)carbazole (I) are added 65 ml of methyl alcohol, and the mixture is boiled with a reflux condenser for 10 min. On cooling, 8.55 g (71.2% of theory) of 9-(α-methoxyethyl)carbazole crystallizes, m.p. 87–89°C.

By an analogous procedure, from 7.6 g and 30 ml of ethanol, first 1.25 g of carbazole crystallizes; it is filtered off, and then 3.96 g (56% of theory) of 9-(α-ethoxyethyl)carbazole crystallizes, m.p. 71–72°C.

Propyl and butyl ethers of 9-(α-oxyethyl)carbazole. The indicated ethers crystallize with difficulty from the corresponding

Ethers of 9-(α-hydroxyethyl)carbazole

Table 1

of the corresponding alcohols; therefore, the following procedure was developed for their isolation.

A mixture of 15.2 g of 1 and 60 ml of propyl alcohol is boiled for 10 minutes. The carbazole that separates on cooling of the solution is filtered off, and the filtrate is neutralized with 40% aqueous alkali solution to an alkaline reaction with phenolphthalein. The aqueous layer is separated, and the solvent is distilled off from the alcoholic layer. The remaining oil is distilled in vacuo; yield 5.9 g (38.8% of theory), m.p. 39–42°C.

Similarly, from 7.6 g of 1 and 30 ml of butanol, 2.9 g (36% of theory) of 9-(α-butoxyethyl)carbazole, m.p. 50–51°C, was obtained.

Further purification of all the ethers was carried out by crystallization from methanol. The properties of all the compounds synthesized by us are given in Table 1.

Conclusions

1. It has been shown that vinyl acetate adds to carbazole in the presence of alkalis, with formation of 9-(α-acetoxy)ethylcarbazole in good yield.

2. Some chemical transformations of 9-(α-acetoxyethyl)carbazole have been studied.

3. A series of ethers of 9-(α-hydroxyethyl)carbazole has been synthesized.

LITERATURE

1. T. Yoshida, H. Hirakawa, J. Chem. Soc. Japan, Ind. Chem. Sec., 55, 83, 1952.

2. J. Furukawa, A. Onishi, T. Tsuruta, J. Chem. Soc. Japan, Ind. Chem. Sec., 60, 170, 1957.

3. R. Flowers, H. Miller, L. Flowers, J. Am. Chem. Soc., 70, 3019, 1948.