Vanadate anion catalyses aerobic hydroxylation of hydrocarbons in acetonitrile in the presence of solid ascorbic acid or zinc and with obligatory participation of pyridine, pyrazine-2-carboxylic acid and acetic acid as mediators of proton and electron transfer. If sufficient amount of water is present in the reaction mixture, ascorbic acid is dissolved in aqueous acetonitrile and no hydroxylation occurs in this case. The dependencies of the product yields on the concentrations of the reactants have been studied and a mechanism of the formation of hydroxyl radicals has been proposed. These systems mimic generation of hydroxyl. radicals in certain vanadium-dependent biological processes. (C) 2002 Elsevier Science B.V. All rights reserved.