Carbazole, nitrosation

The N-nitrosation of carbazoles is a well-established process, several more examples of which have been described sodium nitrite in acetic acid is the most frequently used reagent. 

Nitrosocarbazole condenses with 9-aminocarbazole to give the azo compound 122, heating of which produces dimers in a ratio similar to that observed by oxidation of carbazole (see Section II,A,2) it was therefore believed to involve the carbazol-9-yl radical. 3-Nitro-9-nitrosocarbazole was shown to serve as a nitrosating agent for A-methylaniline it converted aziridine to ethene and nitrous oxide. ... 

A mechanistically intriguing transformation resulted when 9-aminocarbazole formed salt 137 via the reaction of its Grignard derivative with dibromo-triphenylphosphorane. Reaction of the salt 137 with ethyl nitrite gave 3-bromocarbazole the authors speculate that nitrosation followed by nitrogen loss generates the carbazol-9-yl cation, attacked in a nucleophilic sense by bromide at C-3. ... 

Carbazoles normally react with electrophiles to yield the 3-monosubstituted and 3,6-disubstituted derivatives. Further reaction may occur at the 1- and the 8-positions. There is evidence that the initial reaction occurs at the 9-position. Thus, nitrosation of carbazole with sodium nitrite in acetic acid yields 9-nitrosocarbazole which, when treated with nitric acid, is converted into 3-nitrocarbazole (09CB3797) and 3,6-dinitrocarbazoIe (46USP2392067). Direct nitration of carbazole with nitric acid (02GEP128853) or with ethyl nitrate also yields the 3-nitro and 3,6-dinitro derivatives, together with 1,3,6,8-tetranitrocarbazole (27CB738). 

Nitrosation, acetonedicarboxylic acid, 96 carbazole, 218 o-cresol, 203 dimethylaniline, 115 ethyl malonate, 153, 156... 

---