Investigation of trialkoxysilane hydrolysis kinetics using liquid chromatography with inductively coupled plasma atomic emission spectrometric detection and non-linear regression modeling

A novel approach is demonstrated for measuring rates of the consecutive acid-base catalyzed hydrolysis reactions of (3-glycidoxypropyl)trimethoxysilane (GPTMS) and (3-aminopropyl)triethoxysilane (APTES) in dilute aqueous solution using liquid chromatography with inductively coupled plasma atomic emission spectrometric (ICP-AES) detection. The hydrolysis reactions are monitored by sampling kinetic solutions in a timewise manner and performing liquid chromatographic separations of the parent silane and organosilicon hydrolysis products. The column effluent is fed into the ICP through a direct injection nebulizer for online monitoring of silicon atomic emission at 251.611 nm, producing a series of silicon chromatograms for each kinetic run. Reversed phase separations are effected using acetonitrile-water gradients and are complete in 6 min or less. The systematic changes in peak areas provide information from which the rate constants of the consecutive hydrolysis reactions (k₁, k₂, and k₃) are obtained by non-linear regression modeling. Using a quenching scheme, hydrolysis half-lives as brief as 3 min for the parent silane can be monitored. For each compound, a series of rate constants are obtained over a range of pH and buffer concentration, permitting estimation of the catalytic constants k_H3O⁺ and k_OH⁻ for the consecutive acid-base catalyzed hydrolysis reactions by multiple regression analysis.