Kinetics of the Thiazolium Ion-Catalyzed Benzoin Condensation
- 23 June 2001
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 66 (15) , 5124-5131
- https://doi.org/10.1021/jo010244h
Abstract
The formation of benzoin (Ph-CHOH-CO-Ph) from two molecules of benzaldehyde, catalyzed by 3-benzyl-5-(2-hydroxyethyl)-4-methylthiazolium bromide in methanol buffered with Et3N/Et3NH+Cl- has been studied. Initial-rate studies at various concentrations of PhCHO (0.1−1.7 M) showed that the reaction is close to being first order in PhCHO. Following the reaction in deuteriomethanol, 1H NMR spectroscopy allowed rate constants for all three kinetically significant steps to be determined. These show that all three steps are partially rate-determining. A normal deuterium kinetic isotope effect for the overall reaction (kH/kD ≈ 3.4) is observed using PhCDO, and a large inverse solvent isotope effect (kD/kH ≈ 5.9) is observed using deuteriomethanol, consistent with the kinetic scheme presented here.Keywords
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