Hydroxylation of benzene catalyzed by selectively site-substituted vanadium(V) heteropolytungstates in the presence of hydrogen peroxide

Using selectively site-substituted vanadium(V) Keggin and Dawson heteropolytungstates (HPA), the catalytic activities for hydroxylation of benzene in the presence of 30% aqueous H2O2 were examined at room temperature under atmospheric pressure in a two liquid phase, aqueous and organic process. In particular, potassium salts of di- and tri-vanadium(V) substituted Keggin HPAs, alpha-1,2-PW10V2 and alpha-1,2,3-PW9V3, showed catalytic turnovers 0.81 and 8.69 for phenol production with excellent selectivity, respectively, for 48 h reaction under the conditions: 0.1 mmol catalyst, 1 mi (11.3 mmol) benzene, 2 mi of acetonitrile and 2 mi of 30% H2O2. The activity of tri-substituted, PW9V3 HPA was initially high, but it maximized after 48 h and its structure completely decomposed, whereas that of di-substituted, PW10V2 HPA gradually increased and exceeded that of the PW9V3 after 120 h. The polyoxoanion structure of the PW10V2 was maintained even after 576 h. Their activities and stabilities as catalysts were compared with those of vanadium(V)-substituted Dawson HPAs (alpha-P2W17V and alpha-1,2,3-P2W15V3), vanadium(V)-containing isopolyanions (IPA; VW5 and V-10), the Milas reagent (V2O5 and aqueous H2O2), and the picolinato-vanadium(V) oxo peroxo complex.