Kinetics of reduction of m-iodonitrobenzene by aqueous ammonium sulfide under liquid-liquid phase transfer catalysis

Hydrogen sulfide generated during hydrotreatment of sour crude oil fractions could be absorbed into aqueous ammonium hydroxide to produce ammonium sulfide. This ammonium sulfide can then be utilized to produce commercially valuable aromatic amino compounds by reducing the corresponding nitro compounds. In this work, the reduction of m-iodonitrobenzene (m-INB) to m-iodoaniline (m-IA) was performed by aqueous ammonium sulfide using a phase transfer catalyst, tetrabutylammonium bromide (TBAB). The study scrutinized the influences of various parameters such as concentrations of TBAB and m-INB, as well as initial sulfide and ammonia concentrations, on the rate of reaction of m-INB. An 11-fold increase in reaction rate was obtained with only 0.09 kmol of catalyst TBAB per cubic meter of the organic phase. The selectivity of m-IA was found to be100%. The reaction was found to be kinetically controlled with an activation energy of 40.0 kJ/mol. The rate of reaction of m-INB was observed to be directly proportional to the concentrations of m-INB, initial sulfide, and catalyst. A pseudo-first order kinetic model was developed to correlate the conversion versus time data and an excellent agreement between observed and predicted reaction rates was obtained. The present work has very high commercial importance as it could be a viable alternative to the traditional Claus process to arrest H2S released by petroleum refineries.