ZrOCl2·8H2O catalysts for the esterification of long chain aliphatic carboxylic acids and alcohols. The enhancement of catalytic performance by supporting on ordered mesoporous silica

Abstract

ZrOCl₂·8H₂O is an efficient catalyst for the esterification of long chain carboxylic acids with long chain primary and secondary alcohols. Supporting ZrOCl₂·8H₂O on ordered mesoporous silica enhances the catalytic activity of the esterification. The esters of C₁₀–C₁₈ normal acid and alcohol are obtained in high yield by supported ZrOCl₂·8H₂O on MCM-41 although the yield of the esters decreases with the chain length of acids and alcohols. The esterification of less reactive branched acids and secondary alcohols gives excellent to good yield of the corresponding esters over supported catalysts. Zirconium cation cluster [Zr₄(OH)₈(H₂O)₁₆]⁸⁺ is suggested as the catalytic active species. The enhancement of catalytic performance by supporting on MCM-41 is due to increased contact between substrate and catalyst because the cation cluster is highly dispersed over MCM-41 with high surface area. The hydrophobic properties of mesoporous silica accelerate the removal of water during the esterification by controlling hydrated water in the cluster. The catalyst is recyclable without significant loss of activity.