Silica-anchored organotin trichloride: a recyclable and clean organotin catalyst for transesterification reactions

A new synthetic scheme towards silica-supported organotrichlorotin derivatives has been developed. It involves the synthesis of (11-triethoxysilyl) undecyltricyclohexyltin, followed by sol-gel processing and, subsequently in the formation of the resulting hybrid silica, by electrophilic substitution of the tricyclohexyltin function by the target grafted trichlorotin using tin tetrachloride. HR-MAS Sn-119 and CP-MAS Si-29 NMR combined with N-2-sorption and TEM measurements evidenced the formation of a mesoporous organic-inorganic hybrid silica including a functionally pure supported-organotrichlorotin species. This silica-grafted organotrichlorotin displays a satisfactory catalytic activity in the transesterification of ethyl acetate by 1-octanol. The catalyst could be recycled four times without significant loss of activity. Furthermore, tin leaching below 10 ppm evidences the benefits of the proposed strategy to limit tin contamination of the final products.