Journal of the Chemical Society. Perkin transactions II p. 1777 - 1780 (1984)
Update date:2022-08-04
Topics:
Schuchmann, Man Nien
Al-Sheikhly, Mohamed
Sonntag, Clemens von
Garner, Anthony
Scholes, George
Isopyrimidines are formed as a result of the oxidation of the 6-yl radicals derived by .OH attack on pyrimidines and dihydropyrimidines.The kinetics of the rearrangement of the isopyrimidines into the corresponding pyrimidines has been followed by pulse radiolysis.The rearrangement of isouracil into uracil is proton-catalysed (k 1.8E7 l mol-1 s-1).Around pH 7 a spontaneous reaction, k 3000 s-1, is observed.On increasing the pH the isouracil deprotonates at N(3) (pKa ca. 9.4).The spontaneous rearrangement of the isouracil anion is considerably slower (k -1).At pH > 10.5 an OH(1-)-catalysed reaction sets in (k 4.9E5 l mol-1 s-1) which involves a second deprotonation, at C(5).Similar results have been obtained for the rearrangement of 5-hydroxyisouracil into isobarbituric acid.On blocking the N(3) position as in 3-methylisouracil, the OH(1-)-induced rearrangement sets in at a much lower pH (pH-1 s-1) than that observed in the other two systems.
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