RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

XXIII. SYNTHESIS OF 3-CHLORO- AND 3,6-DICHLORO-9-VINYLCARBAZOLES

V. P. Lopatinskii, I. P. Zherebtsov

(Presented by the scientific seminar of the problem laboratories of the Chemical-Technological Faculty)

It is known that polymers and copolymers of 9-vinylcarbazole possess valuable technical properties [1,2]. The synthesis of 9-vinylcarbazoles with substituents in the benzene rings of carbazole was of interest for the subsequent study of their influence on the properties of the monomers and polymers.

The present communication describes the synthesis of 3-chloro- and 3,6-dichloro-9-vinylcarbazoles.

3-Chloro-9-vinylcarbazole was previously obtained by vinylation of carbazole with acetylene [3] and is described as a substance with m.p. 69°C. However, the severe conditions of Reppe vinylation and, as our observations have shown, the high tendency of the monomer thus obtained toward thermal polymerization make this method of synthesis of little practical acceptability. Another route for the synthesis of 3-chloro-9-vinylcarbazole consists in using 3-chloro-9-(β-hydroxy)ethylcarbazole as an intermediate product. Preliminary experiments showed that dehydration of 3-chloro-9-(β-hydroxy)ethylcarbazole over caustic potash under the conditions for dehydration of 9-(β-hydroxy)ethylcarbazole [4] leads to the formation of only insignificant amounts of monomer contaminated with by-products. Therefore we chose a method for synthesizing 3-chloro-9-vinylcarbazole by replacing the hydroxyl group with chlorine in 3-chloro-9-(β-hydroxy)ethylcarbazole by the action of phosphorus pentachloride, followed by dehydrochlorination of 3-chloro-9-(β-chloro)ethylcarbazole with caustic potash in methanol, analogous to the method of Klemo and Perkin [5] described for 9-vinylcarbazole. 3,6-Dichloro-9-vinylcarbazole was synthesized by us in an analogous manner. The substances obtained were identified from the data of elemental analysis and by determination of double bonds by the method of hydrogenation over platinum.

Experimental Part

The starting 3-chloro- and 3,6-dichloro-9-(β-hydroxy)ethylcarbazoles were obtained by the methods described in the preceding communication [6].

3-Chloro-9-(β-chloro)ethylcarbazole

Into a flask equipped with a reflux condenser and a gas outlet tube were charged 10 g of 3-chloro-9-(β-hydroxy)ethylcarbazole, 250 ml of carbon tetrachloride, and 8.2 g of phosphorus pentachloride. The mixture was heated on a water bath for 3 hours. After this the cooled solution

washed with a 5% solution of soda and then with water. The solution was dried over calcium chloride, the solvent was distilled off, and the residue was distilled in vacuo. At 215–220°C (5 mm Hg), 8.1 g of an oil was distilled off, which crystallized on standing. After recrystallization from methanol, 5.65 g (48.5% of theoretical) of fine needles with m.p. 82–83°C was obtained. Recrystallization from hexane raises the m.p. to 86°C. Analyses: found, %: C 63.60; H 4.09; Cl 26.48; N 5.46. Molecular weight (cryoscopy in benzene): 265. C₁₄H₁₂NCl. Calculated, %: C 63.6; H 4.16; Cl 26.9; N 5.36. Molecular weight: 264.06.

3-Chloro-9-vinylcarbazole

To a mixture of 3 g of 3-chloro-9-(β-chloro)ethylcarbazole and 6 g of caustic potash, 50 ml of methanol was added, and the mixture was boiled for 4 h on a water bath with a reflux condenser. On cooling, an oily liquid separated, crystallizing on standing into colorless needles. After two recrystallizations from methanol, the yield of 3-chloro-9-vinylcarbazole with m.p. 68–69°C was 1.95 g (75% of theoretical).

3-Chloro-9-vinylcarbazole is readily soluble in aromatic hydrocarbons and carbon tetrachloride, less soluble in methanol and ethanol and in aliphatic hydrocarbons, and insoluble in water. Analyses: found, %: C 73.82; 73.62; H 3.76; 3.67; N 5.87; 5.77; Cl 15.3. C₁₄H₁₀NCl. Calculated, %: C 73.78; H 3.4; N 6.15; Cl 15.6. Molecular weight (cryoscopy) found: 226.9; calculated: 227.7. Determination of double bonds by hydrogenation over platinum showed that the monomer obtained has a purity of 98%.

On recrystallization of 3-chloro-9-vinylcarbazole from hexane, needles are obtained which do not have a sharp m.p. Softening begins at about 68–70°C and ends at about 200°C, which indicates rapid thermal polymerization. According to literature data [3], 3-chloro-9-vinylcarbazole melts at 69°C.

3,6-Dichloro-9-(β-chloro)ethylcarbazole

Into a flask equipped with a reflux condenser and a gas outlet tube were charged 6 g of 3,6-dichloro-9-(β-hydroxy)ethylcarbazole, 100 ml of carbon tetrachloride, and 4.47 g of phosphorus pentachloride. The mixture was boiled on a water bath for 3 h, washed with water to remove phosphorus oxychloride, and dried over calcium chloride. After removal of the solvent by distillation and repeated recrystallization from alcohol, 2.7 g (42.2% of theoretical) of the substance was obtained in the form of fine needles with m.p. 132°C. Analyses: found, %: C 56.50; H 3.58; Cl 35.26. C₁₄H₁₀NCl₃. Calculated, %: C 56.40; H 3.36; Cl 35.76.

3,6-Dichloro-9-vinylcarbazole

To 2.5 g of 3,6-dichloro-9-(β-chloro)ethylcarbazole were added 10 g of caustic potash and 65 ml of methanol. The mixture was boiled with a reflux condenser for 5 h, during which the substance remained in suspension throughout. After cooling, the precipitate was washed with water and dried. 1.8 g (82% of theoretical) of a substance with m.p. 132°C was obtained. A mixed sample with 3,6-dichloro-9-(β-chloro)ethylcarbazole melts at 110–118°C. The pure substance (from aqueous acetone) consists of shiny scales with m.p. 136°C. Analyses: found, %: C 64.37; H 3.23; N 5.38. C₁₄H₉NCl₂. Calculated, %: C 64.2; H 3.32; N 5.34.

Determination of double bonds by hydrogenation over platinum showed that the monomer has a purity of 97%.

Conclusion

A method has been developed for obtaining 3-chloro- and 3,6-dichloro-9-vinylcarbazoles from 3-chloro- and 3,6-dichloro-9-(β-hydroxy)ethylcarbazoles via the corresponding 9-(β-chloro)ethyl derivatives.

Literature

1. Monomers, collection 2. Izdatinlit, 1953.
2. P. Vashchuk. Chemistry of Monomers, vol. I, Izdatinlit, 1960.
3. Chemistry of Acetylene. Izdatinlit, 1954.
4. V. P. Lopatinskii, E. E. Sirotkina, I. P. Zherebtsov, M. A. Leiman. Proceedings of Tomsk State University, 170, 29, 1964.
5. G. Clemo, W. Perkin, J. Chem. Soc., 125, 1804, 1924.
6. V. P. Lopatinskii, I. P. Zherebtsov, E. E. Sirotkina, S. K. Vereshchagina. Bulletin of the Tomsk Polytechnic Institute, 136, 1964.