Answers are grounded in this paper and cite their sources.
An absolute pKa value of about 36 in acetonitrile is obtained for porphyrin from its reaction with phosphazene bases. The monoanion 1 is stable in aprotic solvents and was characterized by NMR and UV/ Vis spectroscopy. The remaining central proton in the monoanion migrates between the four nitrogen atoms much faster than the two protons in the parent compound.
No takes yet. Share an insight, caveat, or question.
Braun et al. (1994) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: