Studies of the Solvolytic Reactions of Some Carbinyl Chlorides.

Abstract

In the present investigation, an attempt is being made to study the effect of the benzyl group as a para-substituent upon the rates of solvolysis of both phenyl dimethyl carbinyl chloride and I-phenyl ethyl chloride. The two carbinyl chlorides were prepared from the corresponding carbinols by saturation with dry hydrogen chloride gas according to the method of Brown and his co-worker. The two carbinols, being new compounds, were also prepared from p-acetyl diphenyl methane. The two carbinyl chlorides, being unstable, were utilised for rate measurements without any further putification. The rate measurements were made in solvents prepared by mixing the appropriate quantities (v/v) of pure dry acetone and boiled-out distilled water. The volumes of acetone and water were adjusted to give a value of K = 12.60 ± 0.2 x 10-5 sec-1 for phenyl dimethyl carbinyl chloride which is almost identical with that obtained by Brown and his co-workers for the same compound. The rate constants were calculated utilising the equation.

The Kinetic measurements were mode at three different temperatures and from the relation, k = Ae-E/RT, the activation energies for the two compounds were calculated. From the comparative study of the rate constants and the application of the Hammet treatment in its modified form, it could be concluded that the benzyl group should be able to stabilise the transition state for solvolytic reactions, but to a lesser extent than methyl because of the electron withdrawing inductive effect of the phenyl group. Calculations based upon the modified Hammett equation gave a value of -0.1970 for + p–benzyl. By comparison with the value of -0.311 for p–methyl, it is concluded that the methyl group is more superior in stabilising the transition state in these solvolytic displacements than the p-benzyl group. The utility of + values for correlation of reactivities in electrophilic aromatic substitution which has been previously established by Brown and co-workers when applied to our present results establish the activating effect of the p-benzyl group in electrophilic aromatic substitution reactions. These conclusions are in good agreement with the results which are recorded for toluene and diphenyl methane. The two carbinyl chlorides were hydrolysed separately at 25o and the percentage conversion into the corresponding olefins and carbinols were calculated.