Equilibrium constants and rates of dehydration of formaldehyde in buffered solutions of light and heavy water studied at DME

Abstract

By means of d.c. polarography the equilibrium constants of the acid dissociation reaction of formaldehyde in light and heavy water have been determined. The ratio of these constants, KH/KD is equal to 2.5. Using the same method, the product of the equilibrium and rate constants of the formaldehyde dehydration reaction has also been determined in three systems: (1) H2CO in H2O; (2) H2CO in D2O and (3) D2CO in D2O. In order to calculate the rate constants of the formaldehyde dehydration reaction, the equilibrium constants of this reaction have been determined using single sweep voltammetry in both light and heavy water. The ratio of these constants, Kh.H/Kh.D is equal to 1/2.66. With these equilibrium constants the catalytic rate constants of the formaldehyde dehydration reaction have been calculated. The kinetic isotope effects of these constants are: kH2O/kD2O=7.25; kH2BO3−/kD2BO3−=4.7 and kOH−/kOD−=1.5. The values obtained were interpreted considering the dissociation equilibria, zero-point and binding energies, and solvent effects.