Photochemistry of uracils in halogenated solvents

Abstract

The photochemistry of uracil and 1-substituted and 1,3-disubstituted uracils in CHBr₃–CH₂Cl₂ is investigated. Photolysis of uracil leads to the formation of 5,6-dibromo-5,6-dihydrouracil as the main product, with 5-bromouracil as the by-product. In contrast with this the 5-bromouracils are formed as the main products by the photolysis of 1-substituted and 1,3-disubstituted uracils, with the corresponding 5,6-dihydro- and 5-bromo-5,6-dihydrouracils as the by-products. The kinetics of the bromination reaction have also been investigated and based on these results a free radical mechanism is proposed.