Determination of Protonation and Deprotonation Constants of 2 New Corroles by Microspectrophotometric Titration

Protonation and deprotonation constants of two novel corroles containing different substituents, i.e., 1 tri(4-chlorophenyl)corrole(ClPh)3CorH3 and 2 tri(2,4-dichlorophenyl)corrole (Cl2Ph)3CorH3, were determined in nonaqueous media by microspectrophotometric titration. It was found that both of the 2 corroles reacted with trifluoroacetic acid in CH2Cl2 medium to form cations by obtaining a proton. The protonation constants (lgKb) found for the corroles 1 and 2 were 4.2 and 4.0 respectively. It was found also that the 2 corroles lost one proton each to form respective anions in CH3OH and NaOH solution. The deprotonation constants (lgKa) were found to be 3.4 for corrole 1 and 3.5 for corrole 2; and both corroles lost 2 protons by reacting with an alkali in CH2Cl2 medium to form dianions with deprotonation constants (lgβ2) of 7.9 and 11.0, respectively.