Kinetics and mechanism of the hydrogenation of m-dinitrobenzene to m-phenylenediamine Hugo Rojas • Gloria Borda • Marı ´a Brijaldo • Patricio Reyes • Jesu ´ s Valencia Received: 4 July 2011 / Accepted: 25 September 2011 / Published online: 7 October 2011 Ó Akade ´miai Kiado ´, Budapest, Hungary 2011 Abstract 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/TiO 2 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. Keywords m-Dinitrobenzene  Hydrogenation  Catalyst  Initial rate  Kinetic study H. Rojas (&)  G. Borda  M. Brijaldo Grupo de Cata ´lisis (GC-UPTC) Universidad Pedago ´gica y Tecnolo ´gica de Colombia, Escuela de Quı ´mica, Facultad de Ciencias, Av. Norte, Tunja, Colombia e-mail: hurojas@udec.cl P. Reyes Facultad de Ciencias Quı ´micas, Universidad de Concepcio ´n, Casilla 160-C, Concepcio ´n, Chile e-mail: preyes@udec.cl J. Valencia Centro de Cata ´lisis Heteroge ´nea, Departamento de Quı ´mica, Facultad de Ciencias, Universidad Nacional de Colombia, Bogota ´, Colombia e-mail: jsvalencia@unal.edu.co 123 Reac Kinet Mech Cat (2012) 105:271–284 DOI 10.1007/s11144-011-0380-6