Abnormal bis-NHC mediated aerial oxidation of arylaldehydes: highly efficient transformation of arylaldehydes to the corresponding carboxylic acids catalyzed by organic catalysts

Three bis-zwitterionic imidazolium salts (bis-NHCs) bearing different alkyl chains and two 2,4,6-trimethylphenyl groups on their imidazole rings have been synthesized and characterized by NMR, electrospray ionization mass spectrometry (ESI-MS) and X-ray diffraction analysis. A convenient and highly efficient reaction catalyzed by the bis-NHC complexes has been discovered for the oxidation of arylaldehydes to the corresponding carboxylic acids in good yields, under ambient pressure in air and under mild reaction conditions, with excellent functional group tolerance, including halide, ether, alkyl and nitro groups.