RESEARCH IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

78. Maleates of 9-(2-hydroxy)-ethylcarbazoles

I. P. ZHEREBTSOV, N. I. KOPYLOVA, V. P. LOPATINSKII

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

Unsaturated esters of 9-(2-hydroxy)-ethylcarbazoles are of interest as monomers, and some of them have already been synthesized [1, 2].

The present communication describes the synthesis of maleates of 9-(2-hydroxy)-ethylcarbazoles, as well as the preparation of one of the fumarates of this series.

The maleates were obtained by heating maleic anhydride with the corresponding alcohol in a solvent, with azeotropic removal of the water formed, in the presence of an acid catalyst—p-toluenesulfonic acid. The fumarate of 9-(2-hydroxy)-ethylcarbazole is formed when a mixture of maleic anhydride and 9-(2-hydroxy)-ethylcarbazole is heated in the presence of p-toluenesulfonic acid; however, this requires a higher temperature than in the synthesis of the maleates, which permits the conclusion that the maleate isomerizes into the fumarate during the synthesis process.

Experimental Part

Starting materials and reagents. 9-(2-Hydroxy)-ethylcarbazoles were synthesized by the action of ethylene chlorohydrin or ethylene oxide on the corresponding substituted carbazoles. One of them—3-nitro-9-(2-hydroxy)-ethylcarbazole—was obtained by nitration of 9-(2-hydroxy)-ethylcarbazole. The synthesis procedures are given in [3, 4, 5].

Substances having the melting points reported in the literature were used. The remaining reagents had reagent-grade or analytical-grade purity.

Thin-layer chromatography (TLC). Silica gel G according to Stahl [6] was used as the sorbent, and chloroform as the solvent. Chromatography was carried out in a saturated chamber. Spots were detected by observation in UV light and by treatment with iodine vapors.

Synthesis of maleates. To develop the conditions for the synthesis of the maleates, 0.0475 mole of 9-(2-hydroxy)-ethylcarbazole or its substituted derivative, 0.02375 mole of maleic anhydride, and 0.5 g of p-toluenesulfonic acid, dissolved in 100 ml of benzene, were boiled with a reflux condenser equipped with a Dean–Stark trap. Every 2 hours a sample was taken for determination of the acid number and for TLC. It was established that after 6 hours of boiling the acid number ceases to decrease and remains at a constant level. TLC shows that in this case a small amount of 9-(2-hydroxy)-ethylcarbazole is present in the reaction mixture. The facts presented indicate that equilibrium has been established.

Table 1

Effect of boiling time on the acid number in the synthesis of maleates in the presence of a catalyst

Note to Table 1: a) without catalyst,
b) with catalyst.

Similar experiments were also carried out with 3-chloro-9-(2-hydroxy)-ethylcarbazole and 3-nitro-9-(2-hydroxy)-ethylcarbazole. It was observed that the reaction of maleic anhydride with 9-(2-hydroxy)-ethylcarbazole begins rapidly after the reagents are mixed (on the chromatogram the spot of maleic anhydride disappears and a spot corresponding to the acid ester appears). The duration of the reaction is determined by the time required to establish equilibrium in the esterification of the acid ester.

On the basis of the experiments performed, the synthesis of the maleates of 9-(2-hydroxy)-ethylcarbazoles is carried out by boiling the indicated amounts of reagents for 6 hours. The mixture was cooled, washed with a 5% solution of caustic potassium hydroxide, dried over anhydrous sodium sulfate, the solvent was removed by distillation, and the residue was recrystallized from chloroform or chlorobenzene (for the maleate of 3-nitro-9-(2-hydroxy)-ethylcarbazole).

The results of the synthesis of the maleates are presented in Table 2.

Synthesis of the fumarate of 9-(2-hydroxy)-ethylcarbazole. Method 1. In a flask fitted with a reflux condenser and a Dean–Stark trap, 0.0475 mole of 9-(2-hydroxy)-ethylcarbazole, 0.02375 mole of fumaric acid, and 0.5 g of p-toluenesulfonic acid are heated until a homogeneous melt is formed (temperature about 160°C), which is accompanied by vigorous evolution of water vapor. After 10 min, 50 ml of xylene is added to the mixture and boiling is continued for 30 min, after which the cooled mixture is filtered and the precipitate is recrystallized

Table 2

Products obtained

from chlorobenzene, obtaining 9-(2-hydroxy)-ethylcarbazole fumarate in the form of light-green crystals that did not disappear upon repeated recrystallizations with the addition of activated charcoal.

Method 2. A mixture of 9-(2-hydroxy)-ethylcarbazole (0.475 mole) and maleic anhydride (0.02375 mole) with 0.5 g of p-toluenesulfonic acid is fused under the conditions indicated above for method 1 for 1.5 hours (more prolonged heating leads to resinification) and is then treated as in method 1.

The results of the experiments are presented in Table 2.

9-(2-Hydroxy)-ethylcarbazole fumarate differs from its isomeric maleate by very poor solubility in ordinary organic solvents, a high melting point, and an X-ray diffraction pattern. Changes are also observed in the IR spectrum and in its behavior on TLC.

Conclusions

1. Maleates of 9-(2-hydroxy)-ethylcarbazoles have been synthesized.
2. The possibility of isomerizing 9-(2-hydroxy)-ethylcarbazole maleate into the fumarate has been demonstrated.

References

1. G. Natta, P. Longi, E. Pellino, Macr. chem. 71, 212, 1964.
2. V. P. Lopatinskii, I. P. Zherebtsov. Author’s Certificate 181118, B. I. No. 9, 1966.
3. V. P. Lopatinskii, I. P. Zherebtsov, E. E. Sirotkina, S. K. Vereshchagina. Izv. TPI, 136, 11, 1965.
4. V. P. Lopatinskii, I. P. Zherebtsov, N. V. Khomyakova, L. S. Alaberdina. Izv. TPI (in press).
5. V. P. Lopatinskii, I. P. Zherebtsov. Author’s Certificate 183209, B. I. No. 13, 1966.
6. Thin-Layer Chromatography. Edited by E. Stahl. “Mir,” 1965.