Abstract
The kinetics of incorporation of copper into the water soluble porphyrin, obtained by the addition of four molecules of ethylene diamine into protoporphyrin IX dimethyl ester, is studied. For copper ion concentrations comparable to that of the porphyrin, the reaction obeys a simple second order rate law. With a ten fold increase in copper ion the rate tends to a limiting value and the first order specific rate is ca 0·1 min −1 for pH 4·6 at 25°C in acetate buffer. For the displacement reaction of zinc porphyrin with copper a first order specific rate of 4·6 × 10 −3 min −1 at pH 4·65 was observed and this is about 30 times greater than that for the self dissociation of zinc porphyrin. It is attributed to the scavenging of the free porphyrin liberated by copper ions. For both the reactions the mechanism proposed, involves the formation of monoanion from free and complexed porphyrin to be the rate determining step.
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