Substitution of halobenzenes to aniline or phenol, catalysed by copper-exchanged zeolites. Selectivity improvements and reaction pathway

Copper-containing zeolites (mordenite and L) were tested in vapour-phase halo-benzene substitutions with ammonia to form aniline, and with water to form phenol. To investigate the reaction pathway and find the most suitable range of starting materials, chlorobenzene was compared with bromobenzene. The former compound was found to be more reactive than the latter, which is opposite to what is found for liquid phase substitutions. Rate-limiting in the bromobenzene substitution is the decomposition of copper bromide species, formed after the actual substitution. In the substitution of chlorobenzene, especially with water, significant selectivity improvements can be achieved when carbon dioxide is used as the carrier gas instead of the usual nitrogen.