The Chemical Reactivity of Sol−Gel Materials:  Hydrobromination of Ormosils

The chemical reactivity of sol−gel materials prepared via base catalysis from mixtures of Si(OEt) 4 and RSi(OEt) 3, where R is an n -alkenyl group bearing the double bond at the terminal position, was studied through the double-bond hydrobromination addition reaction. The reactivity and kinetics were studied as a function of the length of R and as a function of variations in the material preparation procedure. The initial reaction rates and the total capacity of the materials to act as “bromine sponges” depend inversely on the size of R. This behavior is interpreted, among other parameters, in terms of the formation of early micellar structures of the hydrolyzed RSi(OEt) 3 species. Of the various R residues studied, the most efficient bromine sponge is the allyl residue.