Abstract: Under UV irradiation the photoreaction of pyrimidine bases in aqueous solution has involved three types of reactions, (1) namely nucleophilic addition of water, ethanol, or hydrogen cyanide at the 5,6-double bond; (2) dimerization by addition at the same double bond; (3) ring cleavage. It was reported that the presence of phosphates altered the course of the photolysis process of pyrimidine bases and derivatives under the irradiation of low pressure mercury lamp(LPML, 254 nm), but the role of phosphate in the mechanism was not clear. In previous papers we found a new type of the photoreaction(replacement reaction) of pyrimidine bases in phosphate aqueous solutions under the irradiation of medium pressure mercury lamp(MPML). The photoreaction of 1.0×10^-4 mol/L uracil in 0.05 mol/L phosphate solution by irradiation of MPML was reported and the photoreactive enhancement of uracil by adding phosphate was found, which produced a novel compound. The composition and structure of the compound was identified by elemental analysis, EI-MS, UV, IR, ¹H NMR, ¹³C NMR,³¹P NMR. Filter experiments demonstrate that the wavelengths(190—220 nm) in the spectrum of MPML are responsible for the phosphate-induced enhancement.

Key words: UV irradiation, Uracil, Phosphates, Photolysis product