Sulfo-functionalized
siloxane gels with a variety of surface hydrophobicities
were fabricated to elucidate the effect of the environment surrounding
the Brønsted acid site on their catalytic activity for the hydrolysis
of organic molecules. A detailed structural analysis of these siloxane
gels by elemental analysis, X-ray photoelectron spectroscopy, Fourier-transformed
infrared (FT-IR), and 29Si MAS NMR revealed the formation
of gel catalysts with a highly condensed siloxane network, which enabled
us to quantitatively evaluate the hydrophobicity of the environment
surrounding the catalytically active sulfo-functionality. A sulfo
group in a highly hydrophobic environment exhibited excellent catalytic
turnover frequency for the hydrolysis of acetate esters with a long
alkyl chain, whereas not only conventional solid acid catalysts but
also liquid acids showed quite low catalytic activity. Detailed kinetic
studies corroborated that the adsorption of oleophilic esters at the
Brønsted acid site was facilitated by the surrounding hydrophobic
environment, thus significantly promoting hydrolysis under aqueous
conditions. Furthermore, sulfo-functionalized siloxane gels with a
highly hydrophobic surface showed excellent catalytic activity for
the hydrolytic deprotection of silyl ethers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.