Journal of Organic Chemistry p. 6454 - 6459 (1992)
Update date:2022-08-25
Topics:
Muscio, Oliver J.
Meng, Jialun
Wang, Haisheng
Shi, Songyuan
Rate constants for the hydrolyses of 2-fluoro-1-methylpyridinium iodide (3), 4-fluoroquinaldine (4), and 2-chloro-1-methylpyrimidinium triflate (5) in 2 * 10-3 M aqueous sulfuric acid, in D2O/D2SO4, and in mixed H2O/H2SO4-D2O/D2SO4 media are reported.Significant solvent deuterium kinetic isotope effects are evident, with kH/kD = 2.07 for 3, 1.62 for 4, and 2.12 for 5.The results of the proton inventories for the hydrolyses of 3 and 5 are best fit by a form of the Gross-Butler equation for three nearly equivalent sites with fractionation factors of 0.78.The proton inventory of 4 does not yield a unique solution to the Gross-Butler equation, but the results are also consistent with three transition state sites with nearly equal fractionation factors of 0.72-0.78, as well as an additional transition-state site with Φ > 1 and a reactant site with Φ = 1.These proton inventories are consistent with mechanisms in which nucleophilic addition of water in the rate-determining step is assisted by proton-transfer to a second water molecule, with development of an "immature hydronium ion" in the transition state.Mechanisms with cyclic proton transfer are also consistent, but are less satisfactory as hydrolysis routes.
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