Effects of hydrophobic interaction on the kinetics of the reactions of long chain alkylamines with long chain carboxylic esters of 4-nitrophenol

Abstract

The kinetics of the reactions of some long chain alkylamines with long chain carboxylic esters of 4-nitrophenol have been studied. Hydrophobic interactions caused large increases (up to 10⁷-fold) in the rate of the amine-catalysed (termolecular) reaction, compared with the corresponding reaction of ethylamine with 4-nitrophenyl acetate. In aqueous ethanol, the maximum effect from hydrophobic interaction occurred when the composition of the mixed solvent coincided with the maximum development of structure. In those cases where the hydrocarbon chain of the amine was at least as long as that of the ester, the decrease in the free energy of activation was that predicted from theoretical calculations of the free energy supplied to the transition state by the hydrophobic interaction.