The Catalytic Actions of Lewis Base on the Esterification of Surface Silanols and on the Hydrolysis of the Esterified Silica Gels

Abstract

The silica gels were effectively treated in an autoclave with n-hexane solution of alcohol in the Presence of the propylamine even at an appreciably lower temperature and pressure than the critical point of n-hexanewhich is the usual conditions for the surface-treatment. Since there was no any characteristic absorption due to amine, but marked surface group absorption in IR spectra of thus surface-treated silica gels, the propylamine was found to enhance catalytically the esterification of a surface silanol with an alcohol. The silica gels treated with alcohol were spreaded over the water surface like an oil on water, but these hydrophobic natures were converted into hydrophilic nature by shaking it in a few hours at room temperature after adding ammonia into water phase. The dissolution of surface group and no any trace of ammonia were found from IR absorption spectra of the silica gels after hydrolysis at room temperature in the presence of ammonia. In the absence of ammonia, the dissolutions of the surface group to the same order as mentioned above were found to be necessary to react almost ten hours at 80 to 90°C. These showed that the ammonia promoted significantly the hydrolysis of esterified silica gels. The relationship between surface areas and the numbers of surface group of the esterified silica gels after hydrolysis indicates the same tendency as that presented previously. The mechanism of these catalytic reactions was discussed.