PHOTOCHEMICAL REACTIONS OF PYRIMIDINE DERIVATIVES WITH ACRYLONITRILE IN AQUEOUS SOLUTIONS

Abstract— Ultraviolet excitation of pyrimidine derivatives in aqueous solutions containing acrylonitrile can lead to polymerisation of acrylonitrile and/or photoaddition reactions of acrylonitrile and the pyrimidine. Polymerisation of acrylonitrile induced by excitation of orotic acid occurs even in aerated solutions and is very likely due to radicals derived from excited orotic acid molecuies. Using ¹⁴C-labelied orotic acid, the polymer is shown to contain the pyrimidine. With other pyrimidine derivatives, polymerisation is observed only in deaerated solutions and its low yield did not allow us to determine whether the polymerisation is induced by radicals or by photosensitisation. The role of the lowest excited singlet and triplet states of the pyrimidine derivatives in the photoaddition reaction is discussed. In the case of orotic acid, photoaddition is shown to proceed entirely by way of the triplet state.