On the synthesis and isolation of chlorocarbazoles obtained by chlorination of carbazoles

Abstract

Carbazole (1) undergoes electrophilic aromatic substitution with various chlorinating reagents. Although 3‐chlorocarbazole (1b), 3,6‐dichlorocarbazole (1d) and 1,3,6,8‐tetrachlorocarbazole (1f) obtained by chlorination of carbazole were isolated and characterized sometime ago, 1‐chlorocarbazole (1a), 1,6‐dichlorocarbazole (1c) and 1,3,6‐trichlorocarbazole (1e) had never been isolated from the reaction mixtures. The preparation and subsequent isolation and characterization of 1a, 1b, 1c, 1d, 1e and 1f are reported (mp, tR, Rf, 1H‐ and 13C‐nmr, ms). Physical and spectroscopic properties of 1c are compared with those of 1b and 1d in order to show that the former is the major product obtained in several chlorinating processes. As chlorinating reagents, chlorine in glacial acetic acid, sulfuryl chloride, N‐chlorosuccinimide, N‐chlorosuccinimide‐silica gel, N‐chlorobenzotriazole, and N‐chlorobenzotriazole‐silica gel in dichloromethane and in chloroform have been used and their uses have been compared. The chlorination reaction of different carbazole derivatives such as 2‐hydroxycarbazole (2), 2‐acetoxycarbazole (3), 3‐bromocarbazole (4) and 3‐nitrocarbazole (5) was also studied 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 chlorocarbazoles (Scheme 1). Theoretical and experimental results are discussed briefly.

Photochemistry of 2,6‐D'ichlorodiphenylamine and 1‐Chlorocarbazole, the Photoactive Chromophores of Diclofenac, Meclofenamic Acid and Their Major Photoproducts

“…Compounds 2a, 3a, 3b, 312, 3d and 3e (Chart 1) have been previously described and characterized by their spectral properties (28,29). In our experiments, 'H-NMR and HPLC-MS analyses were used to confirm their structures.…”

A study of substituent effect on 1H and 13C nmr spectra of N‐ and C‐substituted carbazoles

“…[40]. N-Acetylcarbazole (1 e) [41], N-benzoylcarbazole (1 f) [23], Nbenzylcarbazole (1c) [42], 1-bromocarbazole (2c) and 3-bromocarbazole (3 c) [30], 1-nitrocarbazole (2 f) and 3-nitrocarbazole (3f) [26], 1-benzoylcarbazole (2e) and 3-benzoylcarbazole (3e) [23], 1-chlorocarbazole (2 b), 3-chlorocarbazole (3 b) and 3chloro-2-hydroxycarbazole (4 b) [24] and 1-iodocarbazole (2 d) and 3-iodocarbazole (3 d) [25] were prepared according to the procedures described in the literature. 3-Acetyl (4d), 3-benzoyl (4e) and 3-benzenesulphonyl-2-hydroxycarbazole (4f) were prepared by the photo-Fries rearrangement [28].…”

“…Besides, in previous papers we also reported 1 H and 1 3 C nmr data for some C-substituted [23][24][25][26] and N-s u b-stituted carbazoles [27,28] without any substituent chemical shift analysis.…”

“…Faulkner et al [30] have introduced the N-bromosuccinimide -silica gel reagent as a convenient reagent system for the bromination of carbazole and related compounds. Also, we have introduced the N-chlorobenzotriazole -silica gel reagent as a useful chlorination method for carbazole and C-substituted carbazoles [24]. Nevertheless, when we performed the bromination reaction of 2-hydroxycarbazole according to the general procedure in the presence of silica -gel (1 g), the reaction became slower and no improvement on the chemical yield was observed.…”

Convenient Chlorination of Some Special Aromatic Compounds Using N-Chlorosuccinimide

“…The 9H-carbazole was selectively chlorinated at the 3-position; polar solvents (such as DMF, DMSO, MeCN) and a higher temperature might contribute to activation of the position para to the electron-donating NH functional group, favoring the formation of 3-chloro-9H-carbazole in a more satisfactory yield. 5 Interestingly, Bonesi and Erra-Balsells 12 have reported the preparation of 3-chloro-9H-carbazole in fairly low yields (0-37%) through straightforward chlorination with NCS in different solvent systems (NCS in glacial AcOH, NCS in CH 2 Cl 2 and NCS-silica gel in CH 2 Cl 2 ).…”