NMR spectroscopy study of 2-methylbenzoxazolium salts hydroxylation in DMSO-d6 solution

2-Methylbenzoxazolium salts showed an unexpected transformation at room temperature, promoted by residual water present in dimethyl sulfoxide. This transformation was followed up inside of an NMR sample tube using DMSO-d6 as solvent, in a series of representative quaternary ammonium salts with carboxymethyl, ethyl, pentyl and decyl N-alkyl chains, resulting in an exclusive product. The corresponding benzothiazolium and benzoselenazolium salts presented a similar behavior after heating at a temperature of 50 °C with the addition of one drop of D2O for the first of these two salts. This reaction could play a very important role in explaining certain secondary reactions occurring in the preparation of compounds where these salts are precursors, classically in cyanine dye synthesis. Four new benzoxazolols were characterized by NMR spectroscopy and HR FAB-MS.