The nitrobenzene (Nb) carbonylation to carbamate with carbon monoxide in the presence of the PdCl2/Fe/I-2/Py (Py: pyridine) catalyst system is a multi-stage reaction. A number of selected reactions were carried out to elucidate successfully, the nitrobenzene transformations at individual stages of the reaction. Nitrobenzene is used up in the following two reactions, viz. it is reduced to aniline by the ethanol hydrogen, and it performs as an oxidant in the aniline to diphenylurea carbonylation. Carbamate is produced in a reaction of dipherylurea with ethanol. (C) 2004 Elsevier B.V. All rights reserved.