Oxidation of cyclopentene catalyzed by tungsten-substituted molybdophosphoric acids

Abstract

A series of Keggin type tungsten-substituted molybdophosphoric acids (H3PMo12−nWnO40·XH2O) were synthesized and characterized by ICP-AES, FT-IR, TG-DSC, and XRD. The tungsten substitution extent signifi- cantly affected their catalytic activity in the oxidation of cyclopentene and the selectivity of the resultant products. The tungsten-substituted molybdophosphoric acids with tungsten substitution numbers in a range of 3-6.8 exhibited high catalytic activity in the oxidation of cyclopentene. After reaction for 8 h, the conversion of cyclopentene was up to 97%; the oxidation products mainly consisted of glutaraldehyde, cis-1,2-cyclopentanediol and trans-1,2-cyclopentanediol with the yields of ca. 23%, 27%, and 45%, respectively. Na2WO4·2H2O (99%), Na2MoO4·2H2O (99%), Na2HPO4·12H2O (99%), H2SO4 (98%), diethyl ether, aqueous hydrogen peroxide (50%), 2-propanol (99.7%), and cyclopentene (98%), all reagent grade, were purchased from National Shanghai Chemical Co. Ltd. and used as received. Distilled water was used throughout all of the ex- periments. 2. Catalyst Preparation Tungsten-substituted molybdophosphoric acids were prepared by a modified classical ether extraction method. The preparation of a tungsten-substituted molybdophosphoric acid with a desired for- mula of H3PMo11WO40·XH2O is presented as an example: 8.95 g of Na2HPO4·12H2O and 66.54 g of Na2MoO4·2H2O were dissolved in 50 ml and 100 ml of distilled water, respectively. The above-men- tioned solutions were mixed and heated at 90