RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

XXIX. On the Action of Sulfuryl Chloride on Carbazole and Its Derivatives

V. P. LOPATINSKII, I. P. ZHEREBTSOV, S. F. ZELINSKAYA

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

Maccara and Lamberti-Zanardi [1] showed that the action of sulfuryl chloride on carbazole leads to the formation of mono- and dichloro derivatives of carbazole, depending on the ratio of the reagents. They also established that 9-benzoylcarbazole, under the conditions they adopted, is not chlorinated.

Subsequently, chlorination with sulfuryl chloride was extended to 9-alkyl-substituted carbazoles, and it proved possible to introduce three chlorine atoms into the carbazole nucleus [2, 3].

In addition to chloroform, recommended as the medium for carrying out the reaction, carbon tetrachloride [4], glacial acetic acid [5], and its mixture with acetic anhydride [6] were used as solvents. It was found that the purest 3-chlorocarbazole is obtained when dichloroethane is used as the solvent [7].

However, in all known methods of chlorinating carbazole with sulfuryl chloride, the yields of both 3-chloro- and 3,6-dichlorocarbazole are relatively low, which is explained by the formation of isomers and products of deeper chlorination, as well as by losses associated with purification [7, 8]. Therefore, the search for methods that make it possible to obtain the purest chlorocarbazoles, as well as products of deep chlorination, is of definite interest.

The aim of our work was to obtain tetrachlorocarbazole by the action of sulfuryl chloride on carbazole, and also to find conditions under which chlorination of 9-benzoylcarbazole and 3-nitrocarbazole is possible, which is of interest for elucidating the influence of substituents on the reactivity of carbazole derivatives.

As the experimental results showed, the action of four moles of sulfuryl chloride on carbazole in chloroform gives tetrachlorocarbazole with m.p. 213°C, probably identical with the substance obtained in works [9] and [10].

However, even prolonged heating with an excess of sulfuryl chloride of 9-acetylcarbazole, 9-benzoylcarbazole, and 3-nitrocarbazole in carbon tetrachloride, chloroform, dichloroethane, or glacial acetic acid does not lead to chlorination of these substances; i.e., electron-acceptor groups in the 9 position, as well as a nitro group in position 3 of the carbazole molecule, hinder chlorination.

Considering the chlorination of carbazole by sulfuryl chloride as a process of electrophilic substitution, it should have been assumed that the intro-

introduction into the proton-acceptor system accelerates the process in accordance with the generally accepted mechanism of electrophilic substitution [11].

Indeed, the use of pyridine as a catalyst in the chlorination of 9-benzoylcarbazole makes it possible to introduce 2 chlorine atoms into its molecule; however, the 3,6-dichloro-9-benzoylcarbazole obtained further is not chlorinated, which is consistent with the fact of its reduced reactivity in other reactions [12].

Under the action of an excess of sulfuryl chloride in the presence of catalytic amounts of pyridine, 3-nitrocarbazole is smoothly converted into a monochloro derivative, probably 3-chloro-6-nitrocarbazole, previously obtained by another route [13].

The catalytic action of pyridine is also manifested in the reaction of sulfuryl chloride with carbazole, facilitating the course of the reaction under mild conditions and sharply reducing the reaction time. Owing to this, it becomes possible to obtain, for example, 3,6-dichlorocarbazole in a much higher yield than usual [8], since the reaction product does not require further purification.

Experimental Part

Tetrachlorocarbazole. A mixture of 20 g of carbazole, 200 ml of chloroform, and 33 ml of sulfuryl chloride is boiled with a reflux condenser for 1 hour with stirring. After the mixture is cooled to room temperature, the precipitated solid is filtered off, dried, and recrystallized from ethyl alcohol. The yield of substance with m.p. 213°C is 16.3 g (60% of theory).

Analyses:
Found, %: C 46.9; H 1.50; Cl 46.1. C₁₂H₅NCl₄.
Calculated, %: C 47.2; H 1.64; Cl 46.6.

3,6-Dichloro-9-benzoylcarbazole. To 20 g of 9-benzoylcarbazole in 100 ml of chloroform are added 16.1 ml of sulfuryl chloride and 5 ml of a 10% (by volume) solution of pyridine in chloroform. The mixture is heated to 45°C and kept at this temperature with stirring for one hour.

The precipitate formed on cooling is recrystallized twice from dichloroethane, giving 12.7 g (50% of theory) of 3,6-dichloro-9-benzoylcarbazole with m.p. 204°C.

Analyses.
Found, %: Cl 20.02; 20.09. C₁₉H₁₁ONCl₂.
Calculated, %: Cl 19.88.

According to the literature [12], 3,6-dichloro-9-benzoylcarbazole melts at 204°C.

Saponification of the substance obtained with an alcoholic solution of potassium hydroxide gives 3,6-dichlorocarbazole with m.p. 202–203°C; a mixture of this substance with an authentic sample of 3,6-dichlorocarbazole shows no depression of the melting point.

3-Nitro-6-chlorocarbazole. 5 g of 3-nitrocarbazole with m.p. 213°C, suspended in 75 ml of carbon tetrachloride, is mixed with 5 ml of sulfuryl chloride, and 10 drops of pyridine are added to the mixture. After boiling with a reflux condenser for one hour and cooling the mixture, the precipitate is filtered off. They obtain 5.7 g (98% of theory) of chloro-nitrocarbazole, melting in the range 270–280°C. After recrystallization from aqueous dimethylformamide, 3.76 g of substance is obtained in the form of thin yellow needles with m.p. 282°C (on a block). According to the literature, 3-nitro-6-chlorocarbazole melts at 284°C [13].

Analyses.
Found, %: Cl 14.0; 14.25; N 10.95; 11.40; C₁₂H₇O₂N₂Cl.
Calculated, %: Cl 14.36; N 11.32.

Dichlorocarbazoles. To 66.8 g of carbazole in 600 ml of chloroform at room temperature are added 65 ml of sulfuryl chloride and, after thorough stirring, 2 ml of a 10% solution of pyridine in chloroform, after which a spontaneous reaction begins with evolution of gases. The reaction mixture is cooled, the precipitated solid is filtered off and dried, giving 46.5 g of 3,6-dichlorocarbazole with m.p. 202–203°C.

The filtrate is evaporated to 1/3 of the original volume, and an additional amount (9.8 g) of 3,6-dichlorocarbazole with m.p. 198–200°C is isolated by cooling and filtering off the precipitated solid.

From the remaining filtrate the solvent is removed completely, and the residue is distilled under vacuum, collecting the fraction boiling at 220–222°C (6–7 mm Hg). This gives 18.9 g of a substance melting at about 89°C. After three successive recrystallizations from 95% aqueous ethanol and petroleum ether (b.p. 70–100°C), and again from petroleum ether, 3.0 g (3.28% of theory) of a substance is obtained, crystallizing in the form of small plates, with m.p. 113–114.5°C, and representing a dichlorocarbazole of undetermined structure.

The total yield of 3,6-dichlorocarbazole is 56.3 g (61.5% of theory).

Analyses.
3,6-Dichlorocarbazole, found %: C 60.92; H 3.24; Cl 29.95; C₁₂H₇NCl₂.
Dichlorocarbazole (m.p. 113–114.5), found %: C 61.24; H 3.50; Cl 30.06; C₁₂H₇NCl₂. Calculated %: C 61.04; H 2.96; Cl 30.05.

Conclusions

1. It has been shown that carbazole is chlorinated to tetrachlorocarbazole under the action of four moles of sulfuryl chloride.

2. It has been found that pyridine is an effective catalyst for the chlorination of carbazole with sulfuryl chloride, and also of some of its derivatives that are not chlorinated without the use of catalysts.

LITERATURE

1. G. Mazzara, E. Lamberti-Zanardi, Gazz. chim. ital., 26, II, 238, 1896.
2. N. Bun-Hoi, R. Royer, J. Org. Chem., 17, 1198, 1951.
3. N. Bun-Hoi, R. Royer, J. Org. Chem., 15, 123, 1950.
4. I. Ya. Postovskii, R. O. Masevosyan, A. K. Chirkov. ZhOKh, 30, 3190, 1960.
5. G. List, German Patent 275833; C. II, 162, 1914.
6. K. Sugimoto, J. Chem. Soc. Jap., P. C. S., 71, 524, 1950; C. A. 45, 6383, 1951.
7. V. P. Lopatinskii, I. P. Zherebtsov. Methods for the Preparation of Chemical Reagents and Preparations. IREA, 11, 102, 1964.
8. V. P. Lopatinskii, I. P. Zherebtsov, S. K. Vereshchatina. Methods for the Preparation of Chemical Reagents and Preparations. IREA, 11, 56, 1964.
9. P. Chabrier, Ann. chim., 17, 353, 1940; C. A. 38, 3256, 1944.
10. P. Chabrier, Bouigault, Compt. rend., 213, 400, 1941; C. A. 37, 1010, 1943.
11. G. Bekker. Introduction to the Electronic Theory of Organic Reactions. “Mir,” 1965.
12. S. Plant, J. Powell, J. Chem. Soc., 9379, 1947.
13. G. Coker, S. Plant, P. Turner, J. Chem. Soc., 110, 1951.