The Nature of the Reactions between Chlorine and Purine and Pyrimidine Bases: Products and Kinetics

The reactions between chlorine and the bases uracil, cytosine and caffeine in aqueous solutions are under investigation. Caffeine yields a complex array of ring cleavage and rearrangement products in a relatively slow reaction. True ring chlorination with the production of 8-chlorocaffeine occurred in these systems but was a relatively minor process. The reaction was fairly slow, highly pH dependant, and yielded an array of labile combined chlorine species and chloride. Chlorine species analysis gave little evidence of the formation of carbon chlorine bonds. Uracil reacted rapidly with chlorine undergoing considerable true chlorination with the formation of a product consistant in character with 5-chlorouracil. Kinetically, the reaction was strongly pH dependant. While small quantities of chloramines were produced they were labile arising most likely as a result of ring cleavage. Cytosine produced a complex array of products including chromatographable organic chloramines. Fifty percent of chlorine added to cytosine was manifested as combined chlorine of high stability. Evidence for various N-chlorocytosines is presented.