Determination of acidity of di-, tri-, and tetraazaporphyrins in dimethyl sulfoxide-potassium cryptate medium

Acidic properties of 10,20-diaza-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-hexylporphyrin, 2,7,12,17-tetra-t-butyltetrabenzo-5,10,15-triazaporphyrin and octa(n-amyloxy)phthalocyanine in the system of dimethyl sulfoxide-potassium cryptates (DMSO-K[222]OH) at ambient temperature was investigated by the method of spectrophotometric titration. The porphyrins in the DMSO-K[222]OH medium were shown to dissociate sequentially forming mono- and dianions in two steps. The concentration ranges of existence of the anionic forms and the acidity sequence of the studied meso-aza-substituted porphyrins were investigated.