Basicity of octa- and dodecamethyl-substituted tetraphenylporphyrins by phase-transfer spectral potentiometric titration

Abstract

Phase-transfer potentiometric titration with potentiometric pH control in the system chloroform-aqueous electrolyte solution was used to determine basicity constants for octamethyl-substituted tetraphenylporphyrins. The pH ranges were determined, where the dicationic form of octa- and dodecamethylsubstituted tetraphenylporphyrins is prevailing. It was shown that the basicity of tetraphenylporphyrins is increased by methyl substitution of β-hydrogens (formation of octamethyl-substituted tetraphenylporphyrins). Further methylation of the four central nitrogen atoms of the porphyrin (formation of dodecamethyl-substituted tetraphenylporphyrins) extends the dication stability pH range to 12.