RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

XIX. SYNTHESIS OF 9-(α-ETHOXY)ETHYLCARBAZOLE

Yu. P. Shekhirev, V. P. Lopatinskii

(Presented by the scientific seminar of the Faculty of Chemical Technology)

In studying the interaction of vinyl acetate with carbazole in the presence of alkalis, we established that at temperatures below 0°C the reaction leads to the formation of the addition product 9-(α-acetoxy)ethylcarbazole. During crystallization from ethyl alcohol, the latter readily exchanges the acetyl group for an ethoxy group, with formation of 9-(α-ethoxy)ethylcarbazole [1]. For definitive identification of the 9-(α-ethoxy)ethylcarbazole thus obtained, it was decided to carry out its synthesis by another route.

Taking into account the high reactivity of halogens in α-haloethyl alkyl ethers, we considered that the interaction of α-chloroethyl ether with carbazole might lead to the formation of the 9-(α-ethoxy)ethylcarbazole of interest to us.

For the synthesis of α-chloroethyl ether, the method proposed by Lloyd and co-workers was used; it consists in passing dry gaseous hydrogen chloride through a mixture of paraldehyde and ethyl alcohol [3].

The first experiments on the interaction of α-chloroethyl ether with carbazole showed that they react vigorously without a catalyst or solvent. However, the reaction is accompanied by strong resinification, which can be explained by secondary processes caused by the hydrogen chloride evolved during the reaction.

In order to bind the hydrogen chloride, the reaction was carried out in methyl ethyl ketone solution in the presence of solid potassium hydroxide. In this way we succeeded in obtaining 9-(α-ethoxy)ethylcarbazole in a yield of up to 55% based on the carbazole that entered into the reaction. The synthesized product has physical constants and properties coinciding with the literature data [1, 2]. The melting point in a mixture with a sample of 9-(α-ethoxy)ethylcarbazole obtained by the exchange reaction between 9-(α-acetoxy)ethylcarbazole and ethanol shows no depression.

Experimental Part

α-Chloroethyl ether. Into a mixture of 62.1 g of paraldehyde and 62 g of ethanol (95.5%), while cooling with a mixture of snow and salt, 67.4 g of gaseous dry hydrogen chloride was passed. The liquid separa-

separated into two layers; the upper layer was separated, dried over $\mathrm{CaCl_2}$, and subjected to fractional distillation. A fraction with a boiling point of 92–96°C was collected. Yield 42.95 g (30% of theoretical), $n_D^{20}$—1.4033 (literature data: b.p. 92–96°C; $n_D^{20}$—1.4053 [3]). 9-(α-Ethoxy)ethylcarbazole. To a suspension of 10 g of carbazole and 3.3 g of solid KOH in 50 ml of methyl ethyl ketone at 20°C and with stirring, 8.5 ml of α-chloroethyl ether was added dropwise over 2 hours. After completion of the reaction, the mass was poured into alkaline water; a yellow oil separated, which gradually turned into a solid precipitate. The precipitate was filtered off and treated with 50 ml of ethanol while heating to 60°C. The unreacted carbazole (4.03 g) was filtered off. On cooling, a white needle-like precipitate crystallized from the alcohol, m.p. 72–74°C; yield 4.73 g (55.3% based on carbazole that entered into reaction). After two recrystallizations from alcohol the product melts at 75–76°C (literature data: m.p. 74–74.5°C [1, 2]). Found, %: N 5.91; 6.08. $\mathrm{C_{16}H_{17}ON}$, calculated, %: N 5.85.

LITERATURE

1. V. P. Lopatinskii, E. E. Sirotkina, Yu. P. Shekhirev, L. F. Kovaleva, A. N. Yushko. Interaction of carbazole and indole with vinyl ethers. Abstracts of reports of the All-Union Conference on the Chemistry of Five-Membered Nitrogen Heterocycles, Publishing House of Rostov-on-Don State University, 8, 1962.
2. J. Flukawa, A. Onishi, T. Tsuruta, J. Org. Chem., 23, 672, 1958.
3. Lloyd, Swallen, Board, J. Am. Chem. Soc., 52, 654, 1930.