Graphene oxide supported chlorostannate (IV) ionic liquid: Brønsted-Lewis acidic combined catalyst for highly efficient Baeyer-Villiger oxidation in water

Lewis acidic chlorostannate(IV)-based imidazolium ionic liquid ([PmimCl][SnCl 4 ] x IL) was post-grafted on graphene oxide (GO) nanosheets through a silylation process. Characterization results suggested the coexistence of intrinsic carboxylic acid on GO edges and the post-grafted Lewis acidic IL on GO planes in the catalysts. The Brønsted-Lewis acidic combined catalysts of GO/[PmimCl][SnCl4] were highly efficient and universal in Baeyer-Villiger (BV) oxidation in water due to the high water-dispersion, diminished diffusion limitation, enriched surface acid sites, as well as the concerted effects between Brønsted and Lewis acid sites. Only 3.0 mol% of GO/[PmimCl][SnCl4]x ( x = 0.5, 1.0, 1.5) was sufficient for affording almost quantitative yield of a wide range of lactones in water without the need of any organic solvents and cocatalysts, whereas Lewis acidic IL of [PmimCl][SnCl 4 ] 1.0 itself was far less efficient. More importantly, the heterogeneous catalysts were perfectly stable and could be reused several times without significant loss of activity and selectivity.