Kinetics And Mechanism Of Reaction Of Barbituric-Acids With Para-Dimethylaminobenzaldehyde And N,N-Dimethyl-Para-Nitrosoaniline

The condensation reactions of barbituric acid (I) and thiobarbituric acid (II) with p-dimethylaminobenzaldehyde (III) and N,N-dimethyl-p-nitrosoaniline (IV) in methanolic medium have been investigated spectrophotometrically at 10-55-degrees-C. These reactions follow overall second order kinetics, first order each in reactants. The rate-determining step involves dehydration of the aldol intermediate (XI). From the dependence of the rate constants on temperature activation parameters have been calculated. The solvent effect on the reaction rate has been investigated and the rate decreases with decrease in dielectric constant.