Abstract: Nine cobalt 5, 15-di(p-substituted phenyl) cctaalkyl porphyrins were synthesized and the effect of para-phenyl substituents on coordination reaction of porphyrins with cobalt salt was studied. It has been shown that the reaction follows the rate expression: -dH₂P/dt=K_obh[H₂P] and the reaction rate is influenced by substituents: , corresponding to the Hammett relationship. The experimental results shown that the presence of electron-donating substituent improvs the catalytic activity of title compound in hydroquinone oxidation reaction.