Stereoelectronic requirement and effect of ring size on silanol elimination: a kinetic study

Abstract

Acid catalyzed elimination of silanol from the cyclic cis-α,β-dihydroxysilanes 3–8 to cycloalkanones was studied at three different temperatures (298, 313 and 328 K). Silyldiols 3–7 hydrolyzed smoothly, while 8 was resistant to hydrolysis. The observed ease of elimination (reflected in the rate constants) was found to be related to the conformational flexibility of the ring and intramolecular hydrogen bonding. The results have confirmed the requirement of perfect antiperiplanar geometry of the eliminating groups, SiMe₃ and β-OH. The quantitation of the hydrolysis products, the cycloalkanones, was done using the gas chromatographic peak area normalization method using an internal standard. The rate data obtained at three different temperatures were employed to calculate ΔH^‡, ΔS^‡, and ΔG^‡. The rate constants and thermodynamic parameters increase with the ring size. There is an interesting demarcation between these two values for common ring silyldiols and the larger ring silyldiols.