Studies on Phenylpyruvic Acid
2014
Tautomerism, | Sciacovelli, O | Dell 'atti, A | De Giglio, A | Cassidei, L | Tautomerism, I Keto-Enol
The tautomerism of phenylpyruvic acid (PPA) and its sodium salt was investigated. The ¹H and ¹³C spectra of PPA in aprotic solvents and in methanol show almost complete prevalence of the enol form, whereas the keto form prevails only in water. The Z configuration was assigned to the sole enol tautomer present on the basis of the value of the vicinal coupling constant | ³J¹H,¹³COOH |=3.7 Hz. A small amount of the hydrated form of PPA (1-phenyl-2,2-dihydroxyl- propanoic acid) was found in the aqueous solution of its sodium salt and in buffer solution (pD =6) of PPA. By means of infrared spectroscopy one can conclude that crystalline PPA is in the enol whereas its sodium salt is in the keto form. The keto-acid was not obtained in the solid state. The colorimetric method for testing PPA traces in urine depends on the formation of a enol-Fe³⁺ complex (2:1) which appears stable in dimethylsulfoxide (DMSO).
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