RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

16. Synthesis of Some Acetamides of Carbazole and Arbazole and Its 9-Alkyl-Substituted Derivatives

M. M. Sukhoroslova, V. P. Lopatinskii, E. E. Sirotkina,
L. P. Levchenko, T. F. Turchina

(Presented by the Scientific-Methodological Seminar of the Faculty of Chemical Technology)

Mono- and diacetamides of carbazole and its 9-alkyl-substituted derivatives are of interest for the synthesis of carbazolylacetic acids. The literature describes 2-acetamide- and 3-acetamidocarbazoles [1], obtained by the Willgerodt reaction from 2-acetyl- and 3-acetylcarbazoles in yields of 58 and 85%, respectively.

In the present work, the results are given of a study of the synthesis of 3-monoacetamides and 3,6-diacetamides of 9-alkylcarbazoles and 3,6-diacetamide of carbazole from the corresponding acetyl derivatives. Using the preparation of 3-acetamide-9-methylcarbazole and 3,6-diacetamide-9-methylcarbazole as examples, the influence of the principal factors on the yield of the final products was studied. In these experiments it was established that the optimum conditions for the synthesis of 3-acetamide-9-methylcarbazole are: temperature 178–180°C, heating time 6 h, amounts of reagents (per 1 mole of 3-acetyl-9-methylcarbazole): sulfur 1 mole, ammonia 4.7 moles, solvent 1 liter (Table 1). To obtain ammonium polysulfide, 50 g of hydrogen sulfide was added per 1 mole of sulfur. Under the optimum conditions the yield of crude acetamide reaches 96%, but as a result of losses during purification by double recrystallization (from ethanol and benzene), the yield of pure substance decreases to 55%. Dioxane and ethanol are suitable as solvents; in pyridine the synthesis proceeds less successfully. Under the indicated optimum conditions, 3-acetamides of other 9-alkylcarbazoles were obtained, information on which is given in Table 3.

In studying the influence of the principal factors on the yield of 3,6-diacetamide-9-methylcarbazole, it was established that the best results are obtained under the following conditions (Table 2): temperature 180–182°C, reaction time 8 h, amounts of reagents (per 1 mole of 3,6-diacetyl-9-methylcarbazole): sulfur 6 moles, ammonia 20 moles, solvent 2.5 l. The yield of pure 3,6-diacetamide-9-methylcarbazole reaches 70% of theory (Table 3). Under the indicated optimum conditions, 3,6-diacetamides of carbazole and other 9-alkylcarbazoles were obtained, information on which is given in Table 3.

Experimental Part

The starting 3-acetyl- and 3,6-diacetyl-9-alkylcarbazoles were obtained by methods developed by us earlier \([2—9]\).

3-Acetamido-9-methylcarbazole

Into a glass ampule (or a stainless-steel bomb) are placed 2.23 g (0.01 mol) of 3-acetyl-9-methylcarbazole (m.p. 100—101°C), 3.4 ml of ammonium polysulfide obtained by passing hydrogen sulfide

Table 1

Results of several experiments on the synthesis of 3-acetamido-9-methylcarbazole

through a suspension of 0.32 g (0.01 g-atom) of sulfur in 3 ml of concentrated ammonia solution and 10 ml of dioxane purified from peroxides. The sealed ampule is kept in a thermostat at 178—180°C for 6 h, after which it is cooled together with the thermostat. The precipitated solid is filtered off, washed with a dioxane–water mixture (1 : 3), then with water, and dried. Yield of product: 2.28 g, m.p. 195—200°C. After recrystallization from alcohol and then from benzene, 1.3 g (55% of theoretical) of 3-acetamido-9-methylcarbazole is isolated—colorless fine needles with m.p. 211—212°C. Not described in the literature. Analyses. Found, %: N 11.75; 11.99. C\(_{15}\)H\(_{14}\)ON\(_2\). Calculated, %: N 11.75.

Table 2

Results of several experiments on the synthesis of 3,6-diacetamido-9-methylcarbazole

Table 3

3-Acetamido- and 3,6-diacetamido-9-alkylcarbazoles

The 3-acetamides of 9-n-propyl-, 9-isopropyl-, 9-n-butyl-, 9-n-amyl-, and 9-isoamylcarbazoles were obtained analogously, but were isolated by evaporation of the aqueous dioxane solutions (Table 3).

3,6-Diacetamido-9-methylcarbazole.

Obtained from 2.65 g (0.01 mole) of 3,6-diacetyl-9-methylcarbazole (mp 196.5–197.5°C) and 15 ml of ammonium polysulfide in 25 ml of purified dioxane. From the crude product (2.5 g), recrystallized from dimethylformamide, 2.1 g (70% of theoretical) of 3,6-diacetamido-9-methylcarbazole with mp 281.5–283°C was isolated. Not described in the literature. Analyses. Found, %: N 14.76, C₁₇H₁₇O₂N₃.
Calculated, %: N 14.24.

Under analogous conditions, 3,6-diacetamide of carbazole and 3,6-diacetamides of other 9-alkylcarbazoles were obtained (Table 3).

Conclusions

1. The influence of the principal factors on the synthesis of 3-acetamides and 3,6-diacetamides of 9-alkylcarbazoles has been investigated.

2. Under optimal conditions, 15 carbazole acetamides and its 9-alkyl-substituted derivatives not described in the literature were synthesized.

Literature

1. H. Gilman, S. Avakian. J. Am. Chem. Soc., 68, 2104, 1946.

2. V. P. Lopatinskii, E. E. Sirotkina, M. M. Anosova. Izvestiya TPI, 111, 40, 1961.

3. V. P. Lopatinskii, E. E. Sirotkina, L. I. Misailova. Izvestiya TPI, 112, 39, 1963.

4. V. P. Lopatinskii, E. E. Sirotkina. Author’s certificate 158884 (1963); BI No. 23, 1963.

5. V. P. Lopatinskii, E. E. Sirotkina, M. M. Anosova. Trudy TGU, 170, 49, 1964.

6. V. P. Lopatinskii, E. E. Sirotkina. Izvestiya TPI, 126, 62, 1964.

7. V. P. Lopatinskii, M. M. Anosova, L. P. Konkina. Izvestiya TPI, 136, 15, 1965.

8. V. P. Lopatinskii, E. E. Sirotkina, M. M. Anosova. Izvestiya TPI, 136, 18, 1965.

9. V. P. Lopatinskii, E. E. Sirotkina. Methods for the Preparation of Chemical Reagents and Preparations, IREA, issue II, 31, 1964.