Dissociation Equilibrium of Nitroform in Polar Solvents Studied by Pulse Radiolysis

Abstract

The dissociation equilibrium C(NO2)3H --- C(NO2)3+Hsol and the related kinetics have been studied for various solvents (alcohols, acetone, and water) by means of pulse radiolysis. Nitroform anions were produced by radiation-chemical reduction of tetranitromethane which was dissolved in these liquids. The dissociation constant K of nitroform decreases with decreasing dielectric constant; its value ranges from 6.3 x 10-1 M for water to 2.5 x 10-7 M for t-butanol. K is essentially controlled by the rate constant kn for the neutralization of C(NO2)3 by solvated protons (3.4 x 104 M-1 s-1 in water and 5.0 x 109 M-1 s-1 in t-butanol), while the rate of dissociation of C(NO2)3H depends relatively little on the nature of the solvent. A linear relationship has been found between log kn and log A'. Nitroform anions arc also neutralized by proton transfer from solvent molecules. The rate constant for this process does not vary much with the properties of the solvent. Equivalent conductivities for C(NO2)3 + Hsol ion pairs have also been determined.