Solid acid catalysts for converting alkenes and alkanols to carboxylic acids Original Research Article

Tertiary carboxylic acids are presently manufactured by hydrocarboxylation of branched alkenes in the presence of CO, water and a corrosive homogeneous acid. Acidic ion-exchange resins also catalyse the hydrocarboxylation reaction when operated under specific conditions. Critical factors are the use of a moderately polar, non-basic solvent and the maintenance of a very low alkanol or alkene/water concentration in the reactor. Consistently, very good performances were achieved when using the carboxylic acid product as solvent and operating the reaction in a continuous stirred tank reactor (CSTR). The best resins included the Nafion NR50 as well as styrene-based sulphonated resins with high content of acid sites (>4.5 mmol/g) and moderate divinyl-benzene content (8–12%), such as the Amberlyst 15 and 36. By contrast, inorganic solid acids, such as zeolites, sulphated zirconia or heteropoly acids showed marginal activity.