Acid-base equilibria of some 7-dimethylamino-3-phenoxazone derivatives

The acid-base equilibria of some phenoxazine dyes in aqueous-ethanolic solutions were studied spectrophotometrically. The compounds examined were prepared in reagent grade purity, their main spectral characteristics in UV and VIS reagion were found and their dissociation constants were determined in 41% (m/m) ethanol. For the analytically most interesting derivative, gallocyanine methyl ester (IV), the pK values were measured also in solutions with different proportions of ethanol. The colour changes accompanying the protolytic reactions and the factors governing the phenomena are discussed.