Simple pyrimidines. VII. The fine structure of 4,6-dihydroxypyrimidine

Abstract

The ultraviolet spectrum of 4,6-dihydroxypyrimidine is compared with those of N -, O -, and 5-alkylated derivatives of fixed structures corresponding to possible tautomeric forms. In contrast to earlier suggestions in the literature, it is concluded that an aqueous solution consists essentially of 1,4,5,6-tetrahydro-4,6-dioxopyrimidine in equilibrium with a smaller amount of 1,4-dihydro-6-hydroxy-4-oxo-pyrimidine. The existence of the active 6-methylene grouping within the ring is confirmed chemically by a ready condensation of benzaldehyde with the pyrimidine in aqueous solution.