Comparison of oxidation properties of Nb and Sn in mesoporous molecular sieves

Oxidation properties of niobium and tin in mesoporous matrices were investigated in oxidation of cyclic ketones, cyclic olefins and cyclic keto-olefins with hydrogen peroxide as an oxidation agent. Mesoporous molecular sieves of MCM-41 and MCM-48 types were synthesized and niobium and tin were incorporated into the structure. X-ray diffraction and nitrogen sorption isotherms confirmed a high-quality of these mesoporous molecular sieves even after incorporation of Nb and/or Sn. It was shown that niobium selectively oxidizes double bond of the substrates to epoxide followed by further hydration and forms diols and keto-diols in the second step of the reaction. On the other hand, tin carries out Baeyer–Villiger oxidation of cyclic ketones to lactones without further consecutive reactions while Nb is inactive in this reaction. When substrate contains both CC double bond and carbonyl group on the same ring, Nb oxidizes preferentially the double bond with a much higher activity than Sn.

Mesoporous molecular sieves containing Nb and Sn were prepared and used for oxidation of cyclohexene, cyclohexanone and cyclohex-2-en-1-one; Nb oxidizes cyclohexene to epoxide, Sn cyclohexanone to lactone; while Nb oxidizes cyclohex-2-en-1-one preferentially the double bond of cyclohex-2-en-1-one with a much higher activity than Sn. Figure optionsDownload as PowerPoint slide