A Study of Effects of Temperature and Medium on Reaction of Triethylamine with Ethyl Bromide

Abstract

The rate constants of reaction of triethylamine with ethyl bromide have been measured in 13 solvents at the temperatures of 293, 313, 333, and 373 K. The activation entropies in the individual solvents increase when going from nonpolar to dipolar aprotic and polar protic solvents, which is explained by dominant solvation of the basic triethylamine and by formation of highly ordered associates without solvent in the activated complex in nonpolar solvent media. No isokinetic relationship has been found between the activation entropy and activation enthalpy, which indicates different solvent effects on the two quantities. The activation enthalpy and entropy of the reaction investigated are close to those of the reaction of triethylamine with ethyl iodide. Three methods have been used to evaluate the effect of medium at all the temperatures, their success being decreased in the order: Pytela's method - Kamlet-Taft - Koppel-Palm. Irrespective of the temperature, all the methods indicate that the reaction is accelerated by the solvent polarity, the significance of other effects being reflected differently depending on the temperature and the correlation equation used. A complex evaluation involving also the interpretation of the entropy and enthalpy components by means of empiric solvent parameters has shown that the resulting Gibbs energy represents a superposition of different effects of solvents on the two thermodynamic quantities, the solvent effect upon the activation entropy being predominant at the higher temperatures.