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Transition State Structure for the Water-Catalyzed Hydrolysis of p -Nitrophenyl Trifluoroacetate in Acetonitrile

1998; American Chemical Society; Volume: 63; Issue: 18 Linguagem: Inglês

10.1021/jo972027f

1520-6904

Kunisi S. Venkatasubban, Melissa Bush, Eileen Ross, Michael K. Schultz, O. T. GARZA,

Advanced Chemical Physics Studies

The neutral hydrolysis of p-nitrophenyl trifluoroacetate in acetonitrile solvent has been studied by varying the molarities of water from 1.0 to 5.0 at 25 degrees C. The reaction is found to be third order in water. The reaction is also third order in D(2)O and in methanol when D(2)O and methanol replace water as the solvent. The kinetic solvent isotope effect is (kH(2)O/kD(2)O) = 2.90 +/- 0.12. Proton inventories at each molarity of water studied are consistent with an eight-membered cyclic transition state model. In this model, three protons undergo bonding changes. Such an eight-membered transition state model can easily accommodate linear hydrogen bonds for the three transferred protons. These results are consistent with the experimental findings of Bell and Critchlow(1) on the reversible addition of water to 1,3-dichloroacetone in dioxane and the theoretical findings of Wolfe and co-workers(2) on the hydration of formaldehyde.