Esterification of acetic acid with butanol over sulfonic acid-functionalized hybrid silicas

Sulfonic acid-functionalized hybrid silicas with different loading of organic moieties were synthesized by grafting and co-condensation followed by oxidation of the precursor thiol groups with hydrogen peroxide or by in situ oxidation methods involving the oxidation by hydrogen peroxide during the condensation reaction. As determined by photoelectron spectroscopy (XPS) complete oxidation of the thiol groups in the differently prepared materials was achieved at room temperature. In the esterification reaction of acetic acid with butanol the samples prepared by the in situ oxidation method exhibited the best catalytic activity. During recycling test with a selected sample, in spite of some sulfur leaching, stable activity was observed.