Thermodynamics of dissociation of some barbituric acids in aqueous solution

Abstract

Values of pK_a for barbituric acid and five of its alkyl and aryl derivatives have been determined spectrophotometrically at selected temperatures in the range 15–50°. From these values, ΔG°, ΔH, and ΔS° have been calculated at each temperature by use of a FORTRAN computer programme. Equations are given which enable pK_a to be calculated at intermediate temperatures. The relative acid strengths are discussed in terms of inductive effects.