Catalysis by sulfur-promoted superacidic zirconia: condensation reactions of hydroquinone with aniline and substituted anilines

Abstract

Industrially important condensation reactions of hydroquinone with aniline and substituted anilines were carried out with a reusable and easily separable heterogeneous catalyst, namely, sulfur-promoted superacidic zirconia. Detailed kinetic data for these reactions are reported. A comprehensive model accounting mass transfer and kinetic resistances was used to interpret the data. The reactions were found to be overall second-order (first-order with respect to each component). The activation energies for both steps of the reaction between hydroquinone and aniline, and for the first step of the reaction with o-toluidine were found to be 89.40, 60.31 and 46.94 kJ/mol, respectively. The order of reactivity for substituted anilines was p-toluidine > aniline >o-toluidine.