Esterification of Long-Chain Acids and Alcohols Catalyzed by Ferric Chloride Hexahydrate

A variety of multivalent metal salt, many of them are hydrates, were screened as catalysts for the esterification of fatty acids and alcohols. These salts included chlorides, nitrates, sulfates, and acetates of Fe3+, Al3+, Ga3+, In3+, ZrO2+, HfO2+, Zn2+, Co2+, Ni2+, Mn3+, Cr3+, and Cu2+. Ferric salts, particularly, FeCl3 center dot 6H(2)O, were the most active among the salts screened. The esters of primary C10-C18 fatty acids and alcohols were obtained quantitatively from equimolar mixtures in the presence of FeCl3 center dot 6H(2)O (substrate/catalyst (S/C; mol/mol) = 200, reaction period = 6 h, in refluxing mesitylene). Esters of isostearic acid and C10-C18 fatty alcohols were obtained with large quantities and prolonged reaction periods. The esters of aromatic carboxylic acids with cetyl alcohol and bulky steroid alcohols, including cholesterol, with C8-C18 fatty acids, were obtained in high yield. The cationic cluster formed by hydrolysis of the ferric cation is proposed to be the catalytically active species. Such a catalysis is proposed to occur through the activation of the carboxylic acid by ligand exchange from water to the carboxylate moiety, followed by addition of the alcohol.