Catalytic synthesis of isocyanates by carbonylation of nitro compounds in the presence of [Rh(CO)2 Cl]2 promoted by pyridine and pyridine hydrochloride

Abstract

1. Pyridine and pyridine hydrochloride activate [Rh(CO)2Cl]2 in the synthesis of isocyanates by the carbonylation of aromatic nitro compounds; in the presence of the catalyst [Rh(CO)2 Cl]2-Py-PyHCl (weight ratio 1–2∶18∶5), at 205°, a CO pressure of 50 atm, and a time of 40 min, nitrobenzene, 3-nitrotoluene, 4-chloro-nitrobenzene, and 4-methoxynitrobenzene are converted to the corresponding isocyanates in 36–90% yield. 2. The activating effect of Py and Py·HCl apparently consists in the formation from [Rh(CO)2Cl]2 of catalytically active monomeric rhodium complexes, which contain Py, Cl−, and CO as ligands.