Determination of acids and their strength in isobutyl methyl ketone

The dissociation constants of nitrophenoxazines in isobutyl methyl ketone (MIBK) were determined and correlated with the HNP values in acetone. Of the derivatives studied, the strongest acid is 1,3,7-trinitrophenoxazine (pK = 19.8), the weakest, 1-nitrophenoxazine (pK > 26). The compounds have no tendency to homo- or heteroconjugation, and were used as indicators in determination of weak acids in MIBK. Some derivatives of malonic acid and of 1,2,4-triazine as well as the intermediates used in their synthesis were determined; their HNP and pK values were established. The shape of the potentiometric titration curves can be of assistance in solving some structure problems.