Ambient-pressure alkoxycarbonylation for sustainable synthesis of ester.

Abstract

Alkoxycarbonylation reactions are common in the chemical industry, yet process sustainability is limited by the inefficient utilization of CO. In this study, we address this issue and demonstrate that significant improvements can be achieved by adopting a heterogeneously catalyzed process, using a Ru/NbO_x catalyst. The Ru/NbO_x catalyst enables the direct synthesis of methyl propionate, a key industrial commodity, with over 98% selectivity from CO, ethylene and methanol, without any ligands or acid/base promoters. Under ambient CO pressure, a high CO utilization efficiency (336 mmol_estermol_CO^-1h^-1) is achieved. Mechanistic investigations reveal that CO undergoes a methoxycarbonyl (COOCH₃) intermediate pathway, attacking the terminal carbon atom of alkene and yielding linear esters. The origins of prevailing linear regioselectivity in esters are revealed. The infrared spectroscopic feature of the key COOCH₃ species is observed at 1750 cm^-1 (C=O vibration) both experimentally and computationally. The broad substrate applicability of Ru/NbO_x catalyst for ester production is demonstrated. This process offers a sustainable and efficient approach with high CO utilization and atom economy for the synthesis of esters.