Transesterification catalyzed by lanthanum complex grafted upon hydrotalcite as a macroligand

Abstract

Lanthanum species grafted upon hydrotalcite(HT) catalyzed transesterification of various esters in methanol solution. In this system, HT acted as a macroligand for lanthanum species through the complexation of the surface hydroxyl group of HT. HT-like compound containing La(III) in its brucite layer and simple La(III) salts showed low and/or no catalytic activity for the transesterification. The combined system of lanthanum ion and HT (La/HT) was important for demonstrating the catalytic activity. Moreover, the activity of the La/HT catalyst increased by treatment with aqueous alkaline but decreased by the reaction in anhydrous methanol. Since the hydrophilicity around the surface of La/HT was essential in the reaction for the catalytic activity, the substrate containing hydrophilic function was easily transformed. The structure of the active La/HT catalyst generated upon the HT surface might be a dinuclear lanthanum complex having aqua and hydroxo ligands, which acted as general acid and base, respectively. This catalyst was able to reuse by handling with slightly alkaline water.