Kinetics of the acetic acid-catalysed ring-opening reaction of 2-phenyl-4,4-dimethyl-2-oxazolin-5-one with some aminoacid ethyl esters in carbon tetrachloride

Abstract

The kinetic behaviour of the acetic acid-catalysed reaction of 2-phenyl-4,4-dimethyl-2-oxazolin-5-one ( 1) with the ethyl esters of glycine ( 2), dl-α-aminobutyric acid ( 4), α-aminoisobutyric acid ( 5), dl-norvaline ( 6), dl-valine ( 7), dl-leucine ( 8) and dl-phenylalanine ( 9) has been investigated. Within the concentration ranges employed the reactions follow second order kinetics, with no dependence of the experimental rate constant on the initial concentration of 1, just as found previously for the ethyl ester of dl-alanine. To explain the function of the catalyst a cyclic intermediate has been compared with other intermediates proposed for similar reactions. A good correlation has been obtained between the rate constant for the catalysed reaction and Taft's σ* values, showing that the effects of the substituents on the esters are mainly polar and supporting the structure of the proposed intermediate.