Direct Hydroxylation of Benzene to Phenol with Molecular Oxygen over Phase Transfer Catalysts: Cyclodextrins Complexes with Vanadium-Substituted Heteropoly Acids

Abstract

Cyclodextrins (CyDs) complexes with vanadium-substituted heteropoly acids (PMoV n -b-CyDs, n = 1, 2) were prepared by simple mixing and their structures were characterized by FT-IR. Among various catalysts, PMoV 1 -b-CyDs, an efficient phase transfer catalyst, exhibited the highest yield (13.1%) of phenol without observing the formation of catechol, hydroquinone and benzoquinone in direct hydroxylation of benzene to phenol in 80 vol% aqueous acetic acid with molecular oxygen and ascorbic acid used as the oxidant and the reducing reagent, respectively. The influences of the reaction temperature, the pressure of oxygen, the amount of ascorbic acid, the amount of catalyst, and the reaction time on the yield of phenol were investigated to obtain the optimal reaction conditions for phenol formation.

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

“…Various organic units such as aliphatic amines [16], metalloporphyrins [17], and bipyrimidinylplatinum [18] were doped into Keggin heteropolyacids to modify their catalytic performances in oxidation reactions. Recently, we observed the promotion effects of cyclodextrin [19] and pyridine [20,21] in the hydroxylation of benzene to phenol by molecular oxygen and/or hydrogen peroxide when anchoring them to Keggin heteropolyacids.…”

Direct Hydroxylation of Benzene to Phenol with Molecular Oxygen over Pyridine-modified Vanadium-substituted Heteropoly Acids

“…We have attempted the liquid-phase oxidation of benzene to phenol catalyzed by vanadium-substituted heteropoly acids using H 2 O 2 as the oxidant [26] and by phase transfer catalysts (cyclodextrins complexes with vanadiumsubstituted heteropoly acids) using molecular oxygen as the oxidant [27], respectively. In this work, we consider that the secondary structure of the heteropoly acid manifests itself to exhibit an extremely high proton mobility and a ''pseudo-liquid phase'' [28][29][30] that can be facile used in the design of catalysts.…”

Preparation of VO2(B) Nanoflake with Glycerol as Reductant Agent and its Catalytic Application in the Aerobic Oxidation of Benzene to Phenol

“…Many efforts have been made for the process, but the yield for phenol was not satisfactory so far [38,39]. In many reported catalysts systems, such as LaOx/HZSM-5 [40], PMoV 1 -b-CyDs [41], Cu/ZnO [42], etc., some co-reducing agent, such as ascorbic acid, was necessary to achieve the conversion of phenol. The phenol yield is almost negligible without using reducing regent.…”