In the picolinic acid (PA) promoted Cr^VI oxidation of dimethyl sulfoxide (DMSO), the Cr^VI–PA complex formed at the pre-equilibrium step undergoes nucleophilic attack by the S of DMSO to form a positively charged reactive intermediate which experiences an oxygen transfer or a ligand coupling to give the products; the anionic surfactant (SDS) accelerates the process while the cationic surfactant (CPC) retards the reaction.