Effect of the chemical modification of a macrocycle and the acidity of a medium on the spectral properties and basicity of tetraphenylporphyrin in HCl–N,N-dimethylformamide system at 298 K

Abstract

Spectrophotometric titration is used to study the basicity of tetraphenylporphine and its derivatives with electron-donor and electron-acceptor substituents in the 4-positions of meso-aryl fragments (5,10,15,20-tetra(4-R-phenyl)porphine, R:–OH,–NH2,–COOH,–Cl) in a system НСl–N,N-dimethylformamide at 298 K. An equation for calculating the dependence of the Hammett constant (Н₀) on the НСl concentration in a НСl–N,N-dimethylformamide system at 298 K is proposed. It is found that protonation of the intracycle nitrogen atoms of tetrapyrrole macrocycles of the indicated compounds occurs in two stages in this system. The corresponding ionization constants and concentration ranges of the existence of mono- and doubly-protonated dication forms of the indicated compounds are determined. It is found that both the introduction of strong substituents into the macrocycle of porphyrin and the properties of the medium facilitate the formation of mono- and doubly-protonated forms of porphyrins in solutions.