Alkylation of aniline with methyl-tert-butyl ether (MTBE) and tert-butanol over solid acids: product distribution and kinetics

Abstract

tert-Butylanilines are used in pharmaceuticals, pesticides, plastics, additives and dyes. They are usually prepared by reacting aniline in presence of liquid acid catalysts with pure isobutylene or C₄ fraction from naphtha crackers containing isobutylene. These processes suffer from problems of use of highly corrosive liquid acids and also the source of isobutylene. Both C- and N-alkylation are possible in the case of aniline depending on reaction conditions such as temperature, source of isobutylene and type of catalyst. In the current study, several solid acids, majority of which were heteropolyacids (HPAs) supported on different clays, were evaluated with both methyl tert-butyl ether (MTBE) and tert-butanol as alkylating agents in a pressure reactor under autogenous pressure. Twenty percent (w/w) dodecatungstophosphoric acid/K10 montmorillonite clay (DTP/K10) was found to be the most active for alkylation of aniline with both MTBE and tert-butanol. Only C-alkylated products were obtained. The yield of mono-alkylated products was over 84% with a selectivity of 53% to 2-tert-butylaniline with MTBE at 175 °C. With tert-butanol only the mono-alkylated products are obtained at 150 °C with equal isomer distribution. Effects of various parameters on rates and selectivities are discussed. In the presence of DTP/K10, only C-alkylated products were obtained. A reaction mechanism is also described with a kinetic model.