Reduction of nitrobenzene catalyzed by immobilized copper catalyst under carbon monoxide and water

Catalytic activity for reduction of nitrobenzene to aniline (98%) and azobenzene (2%) using a poly(4-vinylpyridine)-immobilized Cu catalyst [Cu(II)/P(4-VP)] under a CO atmosphere in aqueous 2-ethoxyethanol was studied as a function of the various reaction parameters ([Cu], P(CO), T, and nitrobenzene/Cu molar ratio). Reaction rates were first-order in [Cu]tot over 1.0–12.0 wt.% range and in P(CO) over the 6.8–27.2 atm range. The catalytic activity proved to be non-linear in nitrobenzene/Cu ratio over 41–500 molar ratio range. These results suggest that the rate-limiting step is preceded by reversible coordination of nitrobenzene to a carbonyl–Cu(I) immobilized species. A catalytic mechanism consistent with the data is proposed.