ON THE SYNTHESIS AND ISOLATION OF CHLOROCARBAZOLES OBTAINED BY CHLORINATION OF CARBAZOLES

Carbazole (1) undergoes electrophilic aromatic substitution with vario us chlorinating reagents. Although 3-chlorocarbazole (1b), 3,6-dichlor ocarbazole (1d) and 1,3,6,8-tetrachlorocarbazole (1f) obtained by chlo rination of carbazole were isolated and characterized sometime ago, 1- chlorocarbazole (1a), 1,6-dichlorocarbazole (1c) and 1,3,6-trichloroca rbazole (1e) had never been isolated from the reaction mixtures. The p reparation and subsequent isolation and characterization of 1a, 1b, 1c , 1d, 1e and 1f are reported (mp, t(R), R-f, H-1- and C-13-nmr, ms). P hysical and spectroscopic properties of 1c are compared with those of 1b and 1d in order to show that the former is the major product obtain ed in several chlorinating processes. As chlorinating reagents, chlori ne in glacial acetic acid, sulfuryl chloride, N-chlorosuccinimide, N-c hlorosuccinimide-silica gel, N-chlorobenzotriazole, and N-chlorobenzot riazole-silica gel in dichloromethane and in chloroform have been used and their uses have been compared. The chlorination reaction of diffe rent carbazole derivatives such as 2-hydroxycarbazole (2), 2-acetoxyca rbazole (3), 3-bromocarbazole (4) and 3-nitrocarbazole (5) was also st udied and the corresponding chloro derivatives 2a, 2b, 2c, 2d, 3a, 3b, 3c, 3d, 3e, 3f, 4a, 4b, 4c, 4d, 5a and 5b are described for the first time. Semiempirical PM3 calculations have been performed in order to predict reactivity of carbazole (1), substituted carbazoles 2-5 and ch lorocarbazoles (Scheme 1). Theoretical and experimental results are di scussed briefly.