The isomerization of [H2O–CO]+ and [HC(O)OH]+ into [HO–C–OH]+: proton-transport catalysis by CO

Mass spectrometry based experiments show that the m/z 46 ion generated in chemical ionization experiments of CO with a trace of water is not the previously proposed formic acid ion, HC(O)OH+ (1). Instead, the more stable dihydroxycarbene ion, HO–C–OH+ (2) is formed. A mechanistic analysis using the CBS-QB3 model chemistry supports the reaction sequence: (CO)2+ + H2O → H2O–CO+ (3), followed by the CO catalyzed isomerization: 3 + CO → 2 + CO. Solitary ions 1 and 2 do not interconvert, but theory and experiment agree that CO also efficiently catalyzes the conversion 1 → 2.