H2 S-rich aqueous diethanolamine (DEA) solution, which could be obtained from amine treatment units (ATUs) of refineries, was utilized to prepare a value-added chemical, o-anisidine from o-nitroanisole (ONA) with co-production of elemental sulfur. The reduction of ONA was carried out under liquid-liquid mode in presence of phase transfer catalyst (PTC), tetrabutylammonium bromide (TBAB). The effects of DEA concentration and elemental sulfur loading on the conversion of ONA were suitably utilized to establish the stoichiometry and mechanism of the so-called Zinin reduction using H2 S-rich aqueous DEA. The reaction was found to be kinetically controlled with apparent activation energy of 63.6 kJ/mol. The rate of reaction of ONA was also found to be proportional to the concentration of catalyst, to the cube of the concentration of ONA, and to the 1.63 power of the concentration of sulfide. An empirical kinetic model based on experimental observations was developed to correlate the experimentally obtained conversion versus time data. The present work has a very high commercial importance as it can replace the conventional Claus process, which gives elemental sulfur as the only product. © 2006 Elsevier Ltd. All rights reserved.