Enhancement of solubility via esterification: Synthesis and characterization of octakis (ester)-substituted phthalocyanines

Metal-free and metallophthalocyanines (M = Zn, Ni and ClFe) carrying eight hydroxyethylsulfanyl groups at peripheral positions were prepared from 4,5-bis(hydroxyethylsulfanyl)phthalonitrile. The reactivity of the hydroxyethyl groups was demonstrated by esterification of phthalocyanine derivatives with pyridine-4-carboxylic acid and also ferrocenecarboxylic acid in the presence of dicyclohexylcarbodiimide combined with N,N-dimethylaminopyridine or p-toluenesulfonic acid and acetic anhydride. Unlike the parent phthalocyanines, the symmetrically functionalized phthalocyanines with eight ester units were soluble in common organic solvents such as CHCl₃, THF, pyridine and DMF, sparingly soluble in ethanol and acetone and insoluble in water and hexane. The newly synthesized compounds were characterized by elemental analysis, IR, UV-vis, FAB-MS and ¹H NMR spectroscopy.