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KMID : 1059519990430010085
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Journal of the Korean Chemical Society
1999 Volume.43 No. 1 p.85 ~ p.91
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Kinetic Study on the Alkaline Hydrolysis of the Substituted Phenyl N,N-diethyl-P-benzylphosphonamidates
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Shon Kyoung-Hwa
Shin Gap-Cheol
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Abstract
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The second order rate constants for the hydrolysis of substituted phenyl N,N-diethyl-P-benzylphosphonamidates (2,4-(NO2)2, 4-NO2, 4-CN, 4-Cl, 4-H)in 20% dioxane-water (v/v) have been determined by UV/Vis spectrophotometric method at various temperatures. The activation parameters (Ea, ΔH≠, ΔS≠) were calculated from the rate constants and the reaction constant (ρ) was also estimated by Hammett equation. The activation entropies of the title reactions show considerably negative values, this result is not consistent with a dissociative mechanism (EA) in which a positive or a slightly negative value of the entropy of activation should be expected. Further, kinetic evidence for an associative mechanism (AE) was obtained from the linear free energy relationship. By the results of kinetic study for the alkaline hydrolysis of substituted phenyl N,N-diethyl-P-benzylphosphonamidates, it may be concluded that these reactions proceed through an associative mechanism.
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