Hydroxylation of Benzene to Phenol by Molecular Oxygen over an Organic-Inorganic Hybrid Catalyst: Schiff Base Manganese Complex Attached to Molybdovanadophosphoric Heteropolyacid

摘要

The organic-inorganic hybrid catalyst L-Mn-PMoV was prepared simply by combining a schiff base Mn complex (L-Mn, L: N,N'-disalicylidene-1, 6-hexanedi-arnine) with the Keggm-structured molybdovanadophosphoric heteropolyacid (PMoV). The proposed composition and structure of the catalyst were evidenced by TG, elemental analysis, FT-IR, and UV-Vis characterizations. Its catalytic performance was evaluated in the direct hydroxylation of benzene to phenol by molecular oxygen with ascorbic acid as the reducing agent. Various reaction parameters were changed to attain the optimal conditions. The hybrid catalyst has a formula [{Mn(C_(20)H_(22)N2 O2)(Cl)}2(H4PMo_(11)VO_(40))], with the two terminal oxygen atoms in the PMoV Keggin structure coordinately linked to the two Mn(III) ions in two L-Mn units, respectively. It exhibits a remarkably enhanced yield to phenol compared to the pure PMoV due to the synergy effect between the Schiff-base manganese complex and PMoV.