Kinetics and mechanism of base catalysed hydrolysis of barbituric acid

Abstract

A kinetic study of base catalysed hydrolysis of barbituric acid by 0.02–3.00M-sodium hydroxide solution at different temperatures was found to follow the irreversible first-order consecutive reaction path (i).Barbituric acid [graphic omitted] Malonuric acid [graphic omitted] Ammonia (i)

The observed pseudo-first-order rate constants, k_{1, obs} and k_{2, obs}, showed three regions of hydroxide ion dependence. (a) The reciprocal of the rate constants was linearly dependent on the reciprocal of hydroxide ion concentration at low concentration. (b) At relatively higher concentration of hydroxide ion the rate constants were found to be independent of the concentration of hydroxide ion. (c) At high concentration of hydroxide ion the rate constants were found to follow the general relationship (ii). k_obs, =a+b[OH^–]+c[OH^–]²(ii)

The empirical parameters a—c were evaluated using a least-squares technique. A trianionic tetrahedral intermediate is proposed to account for the second power of hydroxide ion in the relationship.