PMR study of reactivity and mechanism of H/D exchange in 5-hydroxypyrimidine-1-oxide series

1. A study has been made of the influence of temperature on the pH of aqueous solutions of 5-hydroxypyrimidine-1-oxide and 4,6-dimethyl-5-hydroxypyrimidine-1-oxide in the pH range 0.5–10.0, at 25–90‡. 2. In the rEaction of H/D exchange of the ring protons in 5-hydroxypyrimidine-1-oxide and 4,6-dimethyl-5-hydroxypyrimidine-1-oxide at 160‡ in the pD interval 0.5–10.0, the anionic; and neutral forms are the most reactive; with pD > 6, the reaction proceeds more readily through the SE1 mechanism, and at lower levels of pD through the SE2 mechanism. In the reaction of 4,6-dimethyl-5-hydroxypyrimidine-1-oxide along the SE2 path, the cationic form also participates. 3. Values have been determined for the rate constants of H/D exchange of ring protons, characterizing the contributions of different forms of these compounds to the reaction of isotope exchange of the ring protons.