Lacunary silicotungstic heteropoly salts as high-performance catalysts in oxidation of cyclopentene

Abstract

• Development of lacunary Keggin heteropoly anions by one-pot simplified process. • Functionalized ionic liquid-based catalysts for efficient oxidation of cyclopentene. • The di-lacunary heteropoly anions shows higher intramolecular oxidative capacity and stability. • In situ FT-IR reveals the reaction trend of intermediates and active species. The development of polyoxometalates for olefin oxidation is critical to achieving the green chemical process of the C5 fraction further processing. Di-lacunary silicotungstic anions were easily obtained by continuously adjusting the pH instead of the traditional step-by-step method, which exhibited excellent performance in the catalytic oxidation of cyclopentene to aldehydes or alcohols. The 93.69% CPE conversion and 97.15% total product selectivity (41.38% for GA and 55.77% for 1,2-diol) were achieved by using H 2 O 2 as the oxidant and acetonitrile as the solvent. Through complementary characterization, it was found that the optimized di-lacunary silicotungstic polyoxometalate retained a complete Keggin structure, and exhibited better catalytic activity and stability than the mono-lacunary or saturated silicodecatungstate because it exposed more catalytic active centers. Furthermore, in situ FT-IR spectra was utilized to monitor the reaction process, revealing the formation of the active species W(O 2 ) on the di-lacunary silicotungstic polyoxometalate and the intermediate epoxycyclopentane during the catalytic oxidation of cyclopentene.