Acid-base properties and keto-enol equilibrium of a 5-substituted derivative of 1,3-diethyl-2-thiobarbituric acid

Abstract

This article deals with spectrophotometric and ab initio studies of 1,3-diethyl-7-hydroxy-5,5,7-trimethyl-2-thioxo-1,2,3,5,6,7-hexahydro-4Hpyrano[2,3-d]pyrimidin-4-one (HDEAC). Acid-base properties for I = 0.25 and in a strongly acidic solution of HCl (I -> 0) were investigated. The obtained value of pK(a) (5.79 +/- 0.02) and -pK(H) (1.68 +/- 0.03) show that this compound is a weaker acid than thiobarbituric acid. For interpretation of the spectrophotometric data the ab initio methods with density functional theory at level PBE0/cc-pVDZ/SMD were used. The most energetically favorable structures for neutral and cationic forms of HDEAC were proposed.