A Comparative Study of Catalysis by Zeolite Encapsulated and Neat Copper o-Phenylenediamine Complexes towards Oxidation of Catechol and 3,5-di-tert-Butylcatechol Using Hydrogen Peroxide1

The kinetics of hydrogen peroxide oxidation of catechol (CAT) and 3,5-di-tert-butylcatechol (DTBC) using neat as well as zeolite encapsulated copper complexes of o-phenylenediamine as catalysts have been investigated by a novel UV-visible spectrophotometric technique. The order with respect to the substrate, hydrogen peroxide, as well as the catalyst was unity for all the reactions. This indicates that the mechanism of the reaction is unaltered by encapsulation of the complex although considerable difference exists in the rate of catalysis. The effects of polarity and pH on the reaction were found to be different for the four reactions, suggesting the existence of a deprotonation equilibria for the catalysts in addition to those for the substrates. The rate of oxidation of DTBC was more than that of catechol in the presence of both the catalysts signifying that the inductive effect dominates over the steric constraints in this case. The present work allowed the determination of the acid dissociation constants of Cu(OPD)2 and YCu(OPD)2 in 1 : 9 methanol–water mixtures.