Epoxidation of alpha-isophorone with amine-modified titania-silica hybrid aerogel: Evidence for Ti-amine interaction

The epoxidation of isophorone with TBHP over unmodified and dimethylaminopr opyl-modified titania-silica aerogels is studied. Organic modification dimi nishes the epoxidation activity of titania-silica, but it also eliminates t he activity in acid-catalyzed side reactions, such as epoxide and peroxide decomposition. Addition of MeOH to an unmodified aerogel has a similar effe ct. These catalytic experiments suggest that (i) electron donation by the a lkylamino groups or MeOH to the Ti active site (Lewis acid) suppresses its acidity and thus the rate of acid-catalyzed oxidation and isomerization rea ctions, and (ii) the surface Si-OH groups (Bronsted sites) of titania-silic a are poor catalysts for epoxide decomposition. (C) 2000 Academic Press.