A spectroscopic study of the acid ionization of porphyrins

Abstract

N-Methyloctaethylporphyrin and the corresponding N-(3-bromo-n-propyl)porphyrin ionize in solutions containing aqueous sodium hydroxide to their monoanions by loss of a single proton. Octaethylporphyrin, aetioporphyrin I, and monoaza-aetioporphyrin I ionize to their dianions by loss of two protons. No evidence for the existence of appreciable concentrations of the monanions of the three compounds in solutions containing sodium hydroxide could be detected by visible spectrophotometry. N-Methyl substitution in a porphyrin increases the acidity of the remaining NH atom.