Aerobic Oxidation of Ethylbenzene Co-catalyzed by N-Hydroxyphthalimide and Oxobis(8-Quinolinolato) Vanadium (IV) Complexes

The mediation effect of vanadium compounds on the N-hydroxyphthalimide (NHPI)-catalyzed aerobic oxidation of ethylbenzene (EB) was investigated at 90 °C in benzonitrile. Among the vanadium mediators examined, a series of oxobis(8-quinolinolato) vanadium (IV) complexes (VIVOQ2), which were prepared by the coordination of 8-hydroxyquinoline or its derivatives with oxobis(2,4-pentanedionate) vanadium (IV) (VIV O(acac)2) showed a better mediation effect than VIVO(acac)2, NH4VO3, and V2O5 and they gave about 60%–69% EB conversion and 97% of acetophenone (AcPO) selectivity under optimum reaction conditions. This is due to the dual catalysis effects of these V mediators on the transformation of NHPI to the phthalimide-N-oxyl (PINO) radical and the decomposition of 1-phenylethyl hydroperoxide to AcPO, as supported by UV-Vis spectral characterization.