Ionic liquid initiates and promotes oxidative esterification of alcohols to esters under metal-free conditions in oxygen.

Stable organic nitroxyl radicals are an important class of catalysts for oxidation reactions, but their wide applications are hindered by their steric hinderance, high cost, complex operation, and separation procedures. Herein, NO2 in DMSO is shown to effectively catalyze the aerobic oxidative cleavage of C(OH)−C bonds to form a carboxylic group, and NO2 was generated in situ by decomposition of nitrates. A diverse range of secondary alcohols were selectively converted into acids in excellent yields in this transition‐metal‐free system without any additives. Preliminary results also indicate its applicability to depolymerize recalcitrant macromolecular lignin. Detail studies revealed that NO2 from nitrates promoted the reaction, and NO2 served as hydrogen acceptor and radical initiator for the tandem oxidative reaction.