Equilibrium acidity constants have been determined for 1, 2, 4-triazolidine-3, 5-dione (urazole), several substituted urazoles, and other related acids, in both dimethyl sulfoxide (DMSO) and aqueous solution. In DMSO, urazole has a pK, of 13.1. In water, urazole has a pK, of 5.8. In general, N-methyl and N-phenyl substituents are found to acidify the urazole moiety, in both DMSO and water. The acidifying effects of these substituents are ...