Formate to Oxalate: A Crucial Step for the Conversion of Carbon Dioxide into Multi-carbon Compounds

The efficient conversion of formate into oxalate could enable the industrial-scale synthesis of multi-carbon compounds from CO₂ by C−C bond formation. We found conditions for the highly selective catalytic conversion of molten alkali formates into pure solid oxalate salts. Nearly quantitative conversion was accomplished by calcination of sodium formates with sodium hydride. A catalytic mechanism proceeding through a carbonite intermediate, generated upon H₂ evolution, was supported by density functional theory calculations, Raman spectroscopy, and the observed changes in the catalytic performance upon changing the nature of the base or the reaction conditions. Whereas the conversion of formate into oxalate by using a hydroxide ion catalyst was previously studied, hydride ion catalysis and the chain reaction mechanism for the conversion involving a carbonite ion intermediate are reported herein for the first time.