CeO2-catalysed one-pot selective synthesis of esters from nitriles and alcohols

Abstract

Thirteen kinds of metal oxides were tested for one-pot selective synthesis of esters from nitriles and alcohols. Ceria (CeO₂) showed more than two orders of magnitude higher activity than the other oxides. CeO₂ acted as a reusable and effective catalyst for the ester synthesis from various nitriles and alcohols under neutral and solvent-free conditions at 160 °C. This method provides a rare example for the synthesis of heteroaromatic esters, which have been difficult to synthesize by conventional catalytic esterification methods. Valuable esters such as picolinic acid alkyl esters and niacin benzyl esters were synthesized, demonstrating a practical aspect of the present method. Kinetic studies suggested the following reaction mechanism: (1) H₂O and ROH dissociate on CeO₂, (2) nucleophilic attack of hydroxyl species (OH^δ−) to the adsorbed nitrile on CeO₂, leading to the formation of the primary amide, (3) nucleophilic attack of alkoxide species (OR^δ−) to the amide as the rate-limiting step.