Ortho-Effect of Reaction of Triethylammonium Ortho-Substituted Benzoates with Phenacyl Bromide

Abstract

The kinetics of the reaction of phenacyl bromide with ortho-substituted

benzoic acids in the presence of triethylamine at 25º,30º

and 35ºC in acetone have been studied. The reaction follows second

order kinetics, first order with respect to phenacyl bromide and first

order with respect to carboxylate. The attacking nucleophile is

assumed to be triethylammonium benzoate ion-pair. Electronreleasing

groups accelerate the reaction, while electron-withdrawing

groups retard the reaction. The large negative entropy of activation

indicates a rigid cyclic transition state. The existence of isokinetic

relationship indicates that the same mechanism operates in the

whole series. The rate data do not obey Bronsted relationship; the

Taft's polar substituent constants and inductive effects of the

ortho-substituents are found to be insignificant. The steric factors

of the ortho-substituents are found to be less important while the

resonance effect for this system is found to be more important in

the reaction series.