Kinetics of Reduction of Nitrochlorobenzenes by Aqueous Ammonium Sulfide under Liquid Liquid-Phase Transfer Catalysis

Abstract

The reduction of nitrochlorobenzenes (NCBs) by aqueous ammonium sulfide to the corresponding chloroanilines (CANs) was carried out in an organic solvent, toluene, under liquid-liquid mode with phase transfer catalyst, tetrabutylammonium bromide (TBAB). The selectivity of CANs was found to be 100%. The reaction rate of m-nitrochlorobenzene (MNCB) was found to be highest among the three NCBs followed by o- and p- nitrochlorobenzene (ONCB and PNCB). The reaction was found to be kinetically controlled with apparent activation energies of 22.8, 19.6 and 9.4 kcal/mol for ONCB, PNCB and MNCB, respectively. The effects of different parameters such as TBAB concentration, concentration of NCB, sulfide concentration, ammonia concentration, and elemental sulfur loading on the reaction rate and conversion were studied to establish the mechanism of the reaction. The rate of reaction of NCBs was found to be proportional to the concentration of catalyst and NCBs and to the cube of the concentration of sulfide.