The hydrogenation of m-dinitrobenzene to m-phenylenediamine was carried out as a model hydrogenation reaction of importance to the pharmaceutical and fine chemicals industries with the aim of investigating the kinetics of the reaction. The effect of different conditions: hydrogen pressure, m-dinitrobenzene concentration, reaction temperature, and weight of catalyst on the conversion of m-dinitrobenzene and the yield of m-phenylenediamine were studied using Pt/TiO2 catalyst. During the kinetic study, the intermediate m-nitroaniline was detected. Therefore, the overall reaction was treated as consecutive reactions: first the reduction of m-dinitrobenzene to m-nitroaniline and then, the reduction of m-nitroaniline to m-phenylenediamine. The apparent activation energies of the reaction were determined in each step, to be 33.4 ± 0.4 and 39.8 ± 0.6 kJ/mol. Those results indicated that the hydrogenation of m-nitroaniline toward m-phenylenediamine is the rate determining step in the hydrogenation of m-dinitrobenzene. Two rate equations assuming Langmuir–Hinshelwood mechanism provided the best fit to the experimental data.
1. Dovell, F, Ferguson, W, Greenfield, H1970Ind Eng Chem Prod Res Dev9:224–229.