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

Abstract

Pyridine(Py)-modified Keggin-type mono-vanadium-substituted heteropoly acids (Py n PMo 11 V, n = 1-4) were prepared by a precipitation method as organic/inorganic hybrid catalysts for direct hydroxylation of benzene to phenol in a pressured batch reactor and their structures were characterized by FT-IR. Among various catalysts, Py 4 PMo 11 V exhibited the highest catalytic activity (yield of phenol 9.0%) with the high selectivity for phenol, without observing the formation of catechol, hydroquinone and benzoquinone in the reaction with 80 vol% aqueous acetic acid, molecular oxygen and ascorbic acid used as the solvent, oxidant and 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. Pyridine can greatly promote the catalytic activity of the Py-free catalyst (H 4 PMo 11 VO 40 ), mostly because the organic p electrons in the hydrid catalyst may extend their conjugation to the inorganic framework of heteropoly acid and thus dramatically modify the redox properties.

Variable products in dielectric-barrier discharge assisted benzene oxidation

“…Keeping into perspective the report of phenol production in some previous condensed phase studies [5,[25][26][27][28][29][30][31][32] the same was verified first. In Fig.…”

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

“…H 4 PMo 11 VO 40 (PMoV) was prepared according to the procedure described in our previous report [20]. MoO 3 (17.77 g, 120 mmol) and V 2 O 5 (1.02 g, 5.61 mmol) were added to 250 mL of deionized water.…”

“…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.…”

Liquid phase hydroxylation of benzene to phenol over vanadyl acetylacetonate supported on amine functionalized SBA-15

“…For example, in the work of Kharat et al [20], SBA-15 was first modified by APTES, and the Keggin type vanadium substituted molybdophosphoric acid was then supported on the amine functionalized SBA-15, which showed good activity and stability in the direct hydroxylation of benzene to phenol, owing to strong acidbase interaction between heteropoly anions and amine group. For improving the stability of the POM catalysts, organic units such as ionic liquids and organic polymers have been used to prepare POM based organic-inorganic hybrid heterogeneous catalysts, such as L-Mn-PMoV [23], PMoV n -b-CyDs [24] and Py n PMo 11 V [25]. Although high activity and convenient recoverability were achieved, complex steps and a serial of solvents were required [26].…”