Supported heteropolycompounds as ecofriendly catalysts for 2,6-dimethylphenol oxidation to 2,6-dimethyl-1,4-benzoquinone

Supported catalysts were prepared by in situ deposition of the cesium salt of H4PMo11VO40. Commercial silica was impregnated to incipient wetness with an aqueous solution of CsNO3. The dried and calcined solid was then impregnated an aqueous solution of H4PMo11VO40. Solids with 40% and 7% (w/w) of Cs3HPMo11VO40 were obtained. To compare on behavior catalytic, a catalyst was prepared by silica impregnation with an aqueous solution of H4PMo11VO40 (40%, w/w), using the incipient wetness technique. Impregnated silica particles showed a homogeneous distribution by scanning electron microscope (SEM). The Keggin structure was preserved for the salt in those catalysts according to the FT-IR and DRS characterization. The acidity of the solids with 40% and 7% (w/w) of Cs3HPMo11VO4 was greater than that of the silica but lower than that of bulk salt. The catalysts were used in the oxidation of 2,6-dimethylphenol with aqueous hydrogen peroxide, in acetonitrile at 20 °C. The reaction was followed by UV–vis spectroscopy. The phenol conversion was 35% at 4 h for H4PMo11VO40/SiO2, 20% at 2 h and 29% at 135 h for 7% Cs3HPMo11VO4/SiO2, and 83% at 98 h for 40% Cs3HPMo11VO4/SiO2. The behavior of the latter was also studied by HPLC technique. Similar results were achieved with both techniques. The Cs3HPMo11VO4/SiO2 catalysts were almost totally insoluble in the reaction mixture.

Different heteropolycompounds were used as catalysts in the synthesis of coumarins from phenols and ethyl acetoacetate. Keggin heteropolyacids were supported on silica and the aluminium salts of these heteropolyacids were prepared. The catalytic activity using several phenols were determined and high yield of product was obtained in the case of 4-methyl-7-hydroxycoumarin, 4-methyl-5,7-dimethoxycoumarin and 4-methyl-7,8-benzocoumarin. The use of microwave radiation increases the reaction yield and mainly decreases the reaction time.Figure optionsDownload as PowerPoint slide