Production Methods
Carboxazole is typically produced through either coal tar extraction or synthetic organic reactions. Industrially, carbazole is isolated from coal tar, where it concentrates in the anthracene distillate. It is separated using selective crystallisation or precipitation techniques involving polar solvents like ketones. In laboratory synthesis, one classic method is the Borsche–Drechsel cyclization, which begins with the condensation of phenylhydrazine and cyclohexanone to form an imine. This intermediate undergoes acid-catalyzed rearrangement and ring closure to yield tetrahydrocarbazole, which is then oxidised, commonly with red lead, to produce carbazole.
