TRANSITION-STATE STRUCTURE FOR THE WATER-CATALYZED HYDROLYSIS OF P-NITROPHENYL TRIFLUOROACETATE IN ACETONITRILE

The neutral hydrolysis of p-nitrophenyl trifluoroacetate in acetonitri le 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 w ater. The reaction is also third order in D2O and in methanol when D2O and methanol replace water as the solvent, The kinetic solvent isotop e effect is (kH(2)O/D2O) = 2.90 +/- 0.12. Proton inventories at each m olarity of water studied are consistent with an eight-membered cyclic transition state model. In this model, three protons undergo bonding c hanges. Such an eight-membered transition state model can easily accom modate linear hydrogen bonds for the three transferred protons. These results are consistent with the experimental findings of Bell and Crit chlow(1) on the reversible addition of water to 1,3-dichloroacetone in dioxane and the theoretical findings of Wolfe and co-workers(2) on th e hydration of formaldehyde.