: Determinations of the dimethyl sulfoxide (DMSO) phase pKa's for urazole (pKa = 13.1) and various (methylated and phenylated) mono- and disubstituted urazoles indicate that replacement of hydrogen with methyl and/or phenyl acidifies the urazole moiety, indicate that the acidifying effects of these substituents are additive, and suggest that the protons bound to the N-l and N-4 atoms in urazole are of comparable thermodynamic acidity. © 1990, American Chemical Society. All rights reserved.