Phase-transfer hydroxylation of benzene with H2O2 catalyzed by a nitrile-functionalized pyridinium phosphovanadomolybdate

Abstract

A new nitrile-tethered pyridinium polyoxometalate (POM) was prepared by anion-exchange of the ionic liquid precursor [N-butyronitrile pyridine]Cl ([C 3 CNpy]Cl) with the Keggin phosphovanadomolybdic acid H 5 PMo 10 V 2 O 40 (PMoV 2 ), and the obtained organic POM salt [C 3 CNpy] 4 HPMoV 2 was characterized by XRD, SEM, TG, 1 H NMR, 13 C NMR, ESI-MS, CHN elemental analysis, nitrogen sorption experiment, and melting point measure. When used as a catalyst, [C 3 CNpy] 4 HPMoV 2 causes the first example of reactioncontrolled phase-transfer hydroxylation of benzene with H 2 O 2 , showing high activity and stable reusability. Based on spectral characterizations and comparisons of reaction results, plus the reversible color change between fresh and recovered catalyst, a unique reaction mechanism is proposed for understanding the highly efficient [C 3 CNpy] 4 HPMoV 2 -catalyzed phase-transfer catalysis. The formation of dissolvable active species [VO(O 2 )] + is responsible for the phase-transfer behavior, while the intramolecular charge transfer and the protonated nitrile in cations accelerate the reaction and favor a better catalyst recovery rate.

Metal oxide-triazole hybrids as heterogeneous or reaction-induced self-separating catalysts

“…Herein, we describe an unprecedented behavior for the hybrid material [MoO 3 (trz) 0.5 ] when used in catalytic olefin epoxidation with H 2 O 2 as oxidant. In a manner similar to that reported with polyoxometalate salts [7,[10][11][12][13][14][15][16][17][18][19][20] a solid-liquid-solid phase transfer takes place, with spontaneous reassembly and selfprecipitation of the original molybdenum oxide-triazole solid upon completion of the reaction. Results with the molybdenum(VI) hybrid are compared with those for the corresponding tungsten (VI) compound, and the catalytic performances of both materials have been further examined for the oxidation of benzyl alcohol and benzaldehyde.…”

“…Since the publication of these two landmark papers, progress on self-precipitating transition metal catalysts has been slow. With some exceptions, such as a redox-switchable phase-tagged ruthenium-based catalyst [9], the solid-liquid-solid phase separation procedures are either reaction-controlled [10][11][12][13][14][15][16][17][18][19][20] or thermoregulated [21][22][23][24], and involve polyoxometalate salts of large organic cations [25].…”

The hydroxylation of benzene to phenol over heteropolyacid encapsulated in silica

“…We had developed the polyoxometalate(POM)-ionic hybrid catalysts and used as efficient and reusable catalysts for the hydroxylation of benzene, which gave phenol in 31.4% with 95.8% selectivity [23]. Furthermore, the encapsulated heteropolyacid (HPA) H 3 PW 12 O 40 was reported to be highly active for the esterification [22].…”

Polyoxometalate-based phase transfer catalysis for liquid–solid organic reactions: a review

“…[1][2][3][4][5][6][7] Homogeneous catalysts usually exhibit high activity but have difficulty in separation, recovery and reuse. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Traditionally, the term "phase transfer catalysis" is reserved for catalysts that mediate the transfer of inorganic ions from an aqueous phase into another organic phase where they bring about a reaction. [6][7][8] Alternatively, many efforts have been devoted to Yu Zhou was develop phase transfer catalysts (PTCs), which are homogeneous during the reaction and heterogeneous at the end of the reaction.…”