Proceedings of the Tomsk Order of the Red Banner of Labor Polytechnic Institute named after S. M. Kirov

Volume 175　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1971

RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

45. Synthesis of the Diallyl Ester of 9-Ethylcarbazole-3,6-dicarboxylic Acid

V. P. Lopatinskii, E. E. Sirotkina, L. A. Ionova, B. F. Nazarov

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

Diallyl esters of aromatic dicarboxylic acids are used for the preparation of heat-resistant polymers. The preparation and polymerization of some of them, for example diallyl phthalate, have been well studied and are of great practical importance [1].

A further increase in the heat resistance of polymers of diallyl esters may be expected if, instead of an aromatic dicarboxylic acid, dicarboxylic acids of the carbazole series are used.

In the present work, data are given on the synthesis of 9-ethylcarbazole-3,6-dicarboxylic acid and its diallyl ester. It should be noted that this acid was first described by Buu-Hoi and Roy [2]; however, the authors do not give the yield values or a number of other details of the synthesis.

9-Ethylcarbazole-3,6-dicarboxylic acid was obtained by us by oxidizing 9-ethyl-3,6-diacetylcarbazole with sodium hypobromite in dioxane, with a yield of more than 90% of theory. Its diallyl ester was synthesized by treating a suspension of the acid in an aromatic solvent (best of all, benzene) with an excess of phosphorus pentachloride, followed by addition of allyl alcohol and heating to 80°C. The yield of the ester reaches 70–75% of theory.

Experimental Part

Starting materials. 9-Ethyl-3,6-diacetylcarbazole was prepared by the method developed by us [3] and had a melting point of 182°C. The sodium hypobromite solution was prepared by mixing, at 0°C, 28 ml of bromine with a mixture of 160 ml of distilled water, 54 g of caustic soda, and 200 g of ice. All other reagents were of “pure” grade.

9-Ethylcarbazole-3,6-dicarboxylic Acid

To a suspension of 20 g of 9-ethyl-3,6-diacetylcarbazole in 600 ml of dioxane, with thorough stirring, the entire quantity of the sodium hypobromite solution indicated above is carefully added in small portions. The mixture is heated at 60°C until the acetyl derivative has completely dissolved and is left overnight. The aqueous layer is separated from the dioxane layer, acidified with hydrochloric acid, and the precipitate of 9-ethylcarbazole-3,6-dicarboxylic acid is filtered off and reprecipitated from a 10% solution of Na₂CO₃. This gives 18.2 g of a substance (91% yield), yellowish-cream in color, melting indistinctly above 320°C.

Analyses, %. Found: N 4.92. \(\mathrm{C}_{16}\mathrm{H}_{13}\mathrm{O}_{4}\mathrm{N}\). Calculated: N 4.90.

Diallyl ester of 9-ethylcarbazole-3,6-dicarboxylic acid

Into a round-bottom flask equipped with a reflux condenser and a stirrer are charged 5 g of 9-ethylcarbazole-3,6-dicarboxylic acid, 250 ml of benzene, and 10 g of phosphorus pentachloride. After 15 minutes the reaction mixture is heated to 70°C and kept at this temperature for 2 hours. All the acid passes into solution; 15 ml of allyl alcohol is added to it from a dropping funnel, and the mixture is heated for 1.5 hours at 80°C. After completion of the reaction, the main quantity of benzene (200 ml) is distilled off, and from the residue 4.75 g of the diallyl ester of 9-ethylcarbazole-3,6-dicarboxylic acid is crystallized (74% of theory). It consists of colorless plate-like crystals with m.p. 138°C. It is readily soluble in acetone, benzene, carbon tetrachloride, and other aromatic solvents. Analyses, %. Found: N 3.87; 3.80. \(\mathrm{C}_{22}\mathrm{H}_{21}\mathrm{O}_{4}\mathrm{N}\). Calculated: N 3.86. Unsaturation (by Martin [4]) is 99.0%.

The monomer obtained polymerizes in the presence of benzoyl peroxide in bulk and in solution, and also copolymerizes with styrene. The study of its polymerization and copolymerization is continuing.

Conclusions

1. The synthesis of the diallyl ester of 9-ethylcarbazole-3,6-dicarboxylic acid has been carried out.

References

1. P. Vatsulik. Chemistry of Monomers. Vol. 1. IL, 1960.
2. N. Bui-Hoi, R. Royer. J. Org. Chem., 15, 123, 1950.
3. V. P. Lopatin’skii, E. E. Sirotkina, L. I. Misailova. Izvestiya TPI, 112, 39, 1963.
4. R. Martin. Anal. Chem., 21, 921, 1949.