On the Rate of Ionization in Aqueous Solution of the Carbon-Hydrogen Bond in Aliphatic Compounds

Abstract

The rate at which the carbon-hydrogen bond ionizes to give protons is studied by exchange with deuterium oxide. A base catalyst such as OD- ion is used. A large number of data are correlated in terms of the rate constants k at 25°. In some cases the calculations required to bring the data to comparable conditions are only approximate. The data are restricted to aliphatic compounds and include measurements on nitrohydrocarbons, acetone, acetaldehyde, acetic acid, acetonitrile, methyl sulfonic acid, halogenated compounds and hydroxl compounds. The velocity constants of ionization range from 103 to 10-7, and the order in which the various substituents affect the rate of the CH ionization is given. The influence of substitution on the ionization constants of carboxylic acids has long been studied from the standpoint of thermodynamics. The ionization of CH is a simpler process than the ionization of COOH and it should be possible to learn more of the mechanism through kinetics.