Reversible and Irreversible ElcB Mechanisms in the Hydrolysis of 2,2,2-Trifluoroethanesulfonyl Chloride: Carbanion Intermediates in Aqueous Acid
Hydrolysis of 2,2,2-trifluoroethanesulfonyl chloride (1) is shown to take place by way of the sulfene (CF3CH=SO2), formed by (a) an irreversible E1cB process over the pH range 1.8-5 with water acting as the carbanion-forming base in the lower pH range and hydroxide anion at higher pH, and (b) a reversible E1cB reaction in dilute acid.
King, James F.,Gill, Manjinder Singh
p. 808 - 811
(2007/10/03)
Evidence for a concerted mechanism in the solvolysis of phenyldimethylsilyl ethers
The trifluoroethoxide-catalyzed trifluoroethanolysis and the hydroxide-catalyzed hydrolysis of a series of phenyldimethylsilyl ethers were examined. A Bronsted plot of the logarithm of the second-order rate constant KTFE for reaction with trifluoroethanol against the pKLG is not linear. The nonlinear plot might be taken as evidence for a change in rate-determining step of a reaction that proceeds through a pentavalent intermediate. However, the Bronsted plot for the hydroxide-catalyzed hydrolysis, where all the leaving groups are of lower pKa than hydroxide, has an identical shape as the Bronsted plot for the trifluoroethanolysis reaction. Therefore, the unusual shape of the Bronsted plots is not due to a change in rate-determining step. It is suggested that the results are most consistent with a one-step concerted mechanism and not with a mechanism involving a pentavalent intermediate.
Xu, Yiying,Dietze, Paul E.
p. 10722 - 10727
(2007/10/02)
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