Intermediates in the Reduction of 5-Halouracils by eaq-1

Article abstract of DOI:10.1021/j100243a034

The radical anions of 5-bromo- and 5-iodouracil produced by the reaction of e_aq^- with the halouracils have been observed in nanosecundum pulse radiolysis experiments by their optical absorption at 330 nm.They decay with half-periods of 7.0 +/- 0.5 and 1.7 +/- 0.3 ns.These short lifetimes contrast with the much longer periods observed for the electron adducts to 5-chloro- and 5-fluorouracil (4.9 and > 15 μs).The uracilyl radical produced by halide elimination from the radical anions has an extinction coefficient not greater than 150 M^-1 cm^-1 at 330 nm and no appreciable absorption at wawelengths longer than 310 nm but reacts with 5-bromouracil to form an addition product which has a broad absorption at 365 nm.The rate constant for this latter reaction, (2.66 +/- 0.09) * 10⁸ M^-1 s^-1, provides a reference against which to compare the rates of competing reactions.The absolute rate constant for abstraction of hydrogen from tert-butyl alcohol by uracilyl radical has been determined to be (2.3 +/- 0.2) * 10⁷ M^-1 s^-1.It is clear that uracilyl radical reacts very rapidly by both addition and abstraction processes, reflecting the ? character of this radical.