关键词: Keggin杂多化合物, Venturello-Ishii催化体系, 混合配位, 降解, ³¹P NMR谱

This paper reported a series of Keggin HPA catalyzed epoxidation reaction of cyclopentene with aqueous hydrogen peroxide. Among them, a catalyst of divacant lacunary [γ-SiW₁₀(H₂O)₂O₃₄](Bu₄N)₄ exhibited the highest activity with a conversion of 90% and a selectivity of 98%. UV-vis and FT-IR spectra suggested the maintenance of the γ-Keggin framework of [γ-SiW₁₀(H₂O)₂O₃₄](Bu₄N)₄ in the recovered catalyst. Among HPA compounds with central heteroatom being phosphorus combined with cetylpyridinium bromide as a phase transfer reagent, H₃PMo_12－nW_nO₄₀•mH₂O (n＝1～11) of mixed coordination showed better activity than H₃PW₁₂O₄₀•mH₂O and H₃PMo₁₂O₄₀•mH₂O. But among heteropoly acids H₃PMo_12－n- W_nO₄₀•mH₂O with mixed addendum atoms of Mo and W, H₃PMo₆W₆O₄₀•mH₂O exhibited the highest activity. The fresh catalyst and the catalyst under reaction conditions were characterized by UV-vis, FT IR and ³¹P NMR spectroscopy methods. Under the action of 50 equiv. of H₂O₂, H₃PMo₆W₆O₄₀•mH₂O could be degraded completely to form several new phosphorus-containing species, which may be the catalytic active matter for this reaction. While under the same reaction condition, most of the H₃PW₁₂O₄₀•mH₂O still kept the Keggin structure. Only part of H₃PW₁₂O₄₀•mH₂O was degraded to form one phosphorus-containing species, which is a new tungstophosphate compound and not the {PO₄[WO(O₂)₂]₄}^3－ anion known as the active species in Venturello-Ishii system.

Key words: Keggin HPA, Venturello-Ishii system, mixed coordination, degradation, ³¹P NMR