Regioselective sulfonation of 2-porphyrinylthiophene under kinetic and thermodynamic control

Sulfonation of meso-tetra(thien-2′-yl)porphyrin with concentrated sulfuric acid was found to produce several tetrasulfonated meso-tetra(thien-2′-yl)porphyrin isomers, where sulfonic acid groups were substituted at the 5- or the 4-positions of the thienyl groups, and the tetrasodium salts of the isomers were successfully isolated by reversed-phase HPLC. Temperature dependence of the production ratio of the isomers revealed that sulfonation reactions at the 5- and the 4-positions of 2-porphyrinylthiophene occur under kinetic and thermodynamic control, respectively.