Different Strategies to Anchor Organotin Methoxides on Silica and Their (Re)Use as Heterogeneous Catalysts for Transesterification Reactions

Catalysts were prepared by the heterogenization of the tributyltin(IV) methoxide (n-Bu3Sn(OMe)) and dibutyltin(IV) dimethoxide (n-Bu2Sn(OMe)2) on silica by two strategies: (i) anchoring of the organotin(IV) compounds on silica and (ii) anchoring of the organotin(IV) compounds on a silica gel functionalized with mercaptopropyl groups (SiO2 – SH). The characterization results showed that, regardless of the method used to anchor the organotin species, the solids contained approximately 7-10% of Sn. The decrease or disappearance of the O – H and S – H stretching signals in the SiO2 and SiO2 – SH spectra after the treatment with the organotin(IV) methoxide derivatives suggest the immobilization via O – Sn or S – Sn covalent bonds. The catalytic performance was evaluated in methanolysis of ethyl acetate, in comparison to the analogous homogeneous systems, and the order of reactivity is n-Bu2Sn(OMe)2> n-Bu3Sn(OMe)> SiO2 – SnBu2> SiO2 – S – SnBu2> SiO2 – SnBu3> SiO2 – S – SnBu3. The solids on which the organotin species were directly immobilized on activated SiO2 showed catalytic efficiencies slightly higher than those immobilized on thiol-functionalized silica. All of the solid catalysts were recovered and reused for recycling studies and characterized again after the reuse tests. A better interaction between n-Bu3Sn(OMe) and both supports was observed, as verified by the low leaching of Sn after the first catalytic reaction.
Source: Journal of the Brazilian Chemical Society - Category: Chemistry Source Type: research