Traditional catalysts for the esterification of carboxylic acids such as sulfuric acid and hydrochloric acid, are corrosive and often difficult to remove.'Several new types of catalysts andor methods have been explored, and include hafnium salts, 2 zirconium salts,'scandium salts: diphenylammonium triflate (DPAT), 5 aluminium salts, 6 tetraalkylammonium fluorides,'lanthanide salts, x ion exchange resins,'polyaniline salts,“'zeolites,'','* heteropoly ...
