DYE-SENSITIZED PHOTO-OXIDATION OF BROMACIL IN WATER

Irradiation of an aerated bromacil (3-sec-butyl-5-bromo-6-methyluracil) aqueous solution (250 ppm), by exposure to direct solar radiation in the presence of different dye-sensitizers and an appropriate pH, led to complete and fast photodecomposition of the title compound. The photoreaction mixture spotted on TLC showed one major intermediate, 3-sec-butyl-2-acetyl-2-hydroxy-hydantoin. GLC showed another, minor, intermediate, the 5,5 prime -dimer photo-product of 3-sec-butyl-6-methyluracil. The most effective dye sensitizers checked were riboflavin (10 ppm) and methylene blue (2 to 5 ppm). The rate of reaction was pH dependent, being faster at alkaline pH and almost negligible in acidic solutions. Under optimal experimental conditions the photooxidation was completed after about 1 hour.