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 MeOSO was disclosed, which was generated from esterification between the in situ generated HSO and MeOH, a rate-limiting step in the process. More importantly, the selectivity-controlling step was represented by the subsequent nucleophilic displacement between MeOSO and aldehydes. The ionic oxidant 1a ((NH)SO) with more N-H numbers in the cation, as compared with 1c ((n-BuN)SO) and 1d ((PyH)SO), has better performance in the oxidative esterification of aldehydes.