Abstract 1 H-, 13 C -NMR , IR, UV-Vis, and MS spectra of p-hydroxyphenylpyruvic acid (pH PPA) have been recorded and fully interpreted. pHPPA exists in solution as a mixture of interconverting forms: keto, hydrated keto and only one enol tautomer to which the Z configuration has been assigned according to the value (3.7 Hz) of the vicinal IH-C = C- 13 COOH coupling constant. In organic solvents the enol isomer is far more stable whereas in aqueous solutions the keto form predominates. The tautomeric equilibrium is pH-dependent and the anion is present as keto form not only in aqueous solution but also in H 2 O-DMSO mixtures with a high content of DMSO. The Z enol tautomer does form a coloured complex (λ max = 680 nm) with Fe +3 ions. The complex decomposes rapidly in all considered solvents except DMSO. In view of a possible use of H 2 O-DMSO mixtures for clinical analysis purpose, the enol fraction of pHPPA and the stability of the pH PPA -FeCl 3 com plex in H 2 O-DMSÒ mixtures have been examined. Our results suggest that a solvent com position containing at least 80 vol.% in DM SO could be an appropriate solvent for pH PPA determination by FeCl 3 method.
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Cassidei et al. (1980) studied this question.