Pyrimidine N-oxides. V. Ionization constants of N-hydroxybarbiturates

Abstract

The ionization constants, pK_a, of a number of N-hydroxy 5-substituted barbituric acids and their O-and N-alkylated derivatives are reported. For practical comparisons under physiological conditions, pK_a values were also determined at I 0.15 M KNO₃ and 37º for the clinically useful barbiturates metharbital, phenobarbital and veronal, and for their mono-N-hydroxy derivatives. The pK_a values for N,N?-dihydroxyphenobarbital and the corresponding veronal were also measured.