Kinetics of the pH-Independent Hydrolysis of Bis(2,4-dinitrophenyl) Carbonate in Acetonitrile−Water Mixtures: Effects of the Structure of the Solvent

• DOI: 10.1021/jo970070x
• Publication Date: 2002-07-26T05:11:30Z
• Authors: Omar A. El Seoud; Monica I. El Seoud; João P. S. Farah
• Keywords: 01 natural sciences; 0104 chemical sciences

The pH-independent hydrolysis of bis(2,4-dinitrophenyl) carbonate, DNPC, in aqueous acetonitrile was studied spectrophotometrically from 20 to 45 °C. The binary solvent composition covers [H2O] from 0.02 to 51.39 M, corresponding to the water mole fraction, χw, from 0.100 to 0.971. The dependence of log (kobs), the observed rate constant, on χw is sigmoidal and is similar to the dependence of the solvent polarity scale ET(30) on χw for the same solvent mixture. As a function of decreasing χw, the Gibbs free energy of activation gradually increases, but ΔH⧧ and ΔS⧧ show a complex, quasi-mirror image dependence on χw. Plots of log (kobs) versus log [water] do not allow calculation of a single kinetic order with respect to water over the entire range of [water]. The structure of the transition state was probed by a proton inventory study carried out at χw = 0.453, 0.783, and 0.871, respectively. Plots of observed rate constants versus the atom fraction of deuterium in the solvent curve downward, and the resu...