Vanadium compounds can efficiently catalyse the oxidation of benzene to phenol with molecular oxygen. The reaction is truly catalytic only in the presence of a reducing agent able to recycle the oxidised catalyst. Among the reducing agents tested, ascorbate afforded the highest selectivity and reactivity to phenol. With other reductants, such as dithioalcohols, high selectivity (>96%) was obtained toward more oxidised products (i.e. hydroquinone). The reactions were performed in the two-phase system formed by mixing water/acetonitrile/benzene which allows a good separation between reactant and product. The reaction rate and product selectivity depend upon the type of ligand interacting with vanadium as well as upon the ascorbate/V molar ratio. ESR measurements confirmed that V-IV species is rapidly formed in the reaction medium after the initial addition Of (VCl3)-Cl-III. Moreover, the observed initial induction period of benzene oxidation can be related to the formation of olicomeric V-IV species, as assessed by ESR analysis, rather than to the slow formation of V-ascorbate complex. (C) 2003 Elsevier Science B.V. All rights reserved.