Preparation of proton transfer complex by N-substituted thio barbituric acid with amine bases

The stability constants of proton transfer complex formation of N-phenyl thio barbituric acid (NPTBA). N-o-tolyl thio barbituric acid (NOTTBA). N-m-tolyl thio barbituric acid (NMTTBA) and N-p-tolyl-thio barbituric acid [NPTTBA] with methyl amine dimethyl amine, trimethly amine, ethyl amine, diethyl amine, triethyl amine, n-butyl amine, di-n-butyl amine and tri-n-butyl amine have been determined spectroscopically in 95%(v/v) ethanol-water mixtures. The stabilities of the proton transfer complexes of these N-substituted thio barbituric acids with amine bases have been correlated with the base strength of amines. The composition of proton transfer complexes is determined in solution potentiometrically and spectrophotometrically and substantiated by the element analysis and IR spectra of the isolated complexes. The correlation between mode of enolization in N-substituted thio barbituric acids and the structure of the proton transfer complex is discussed.