Oxidation of Aromatic Aldehydes to Esters: A Sulfate Radical Redox System

A mild oxidative esterification of
various aromatic aldehydes by
sulfate radical redox system was presented. In the reaction pathway
exploration, the transiency of MeOSO3– was disclosed, which was generated from esterification between the
in situ generated HSO4– and MeOH, a rate-limiting
step in the process. More importantly, the selectivity-controlling
step was represented by the subsequent nucleophilic displacement between
MeOSO3– and aldehydes. The ionic oxidant 1a ((NH4)2S2O8) with more N–H numbers in the cation, as compared with 1c ((n-Bu4N)2S2O8) and 1d ((PyH)2S2O8), has better performance in the oxidative esterification
of aldehydes.