Study on the Catecholase Activity in the Presence of a Mn(III)-based Catalyst and Base

Abstract

Background:: This work describes the oxidation of a catechol moiety to the corresponding quinone by using Mn(III)-based catalysts in the presence of an organic base. Two newly reported Mn(III)-Schiff base complexes were utilized for the oxidation of three different substrates, namely, 3,5-di tert-butyl catechol, 1,4-dihydroxy benzene and pyrocatechol, aerobically. Objective:: We intended to understand the role of a base for the above-mentioned oxidation process. Also, we were interested to monitor the progress of reaction using 1H-NMR spectroscopy and to get more insight into the mechanistic path of the reaction. Methods:: The oxidation processes were studied in open air in acetonitrile or methanol solvent. The reaction mixture containing concerned substrate, catalyst, and base were stirred in open air and 1H-NMR spectrum was recorded using the crude reaction mixture in different time intervals. Results:: Interestingly, introduction of a base in the reaction mixture, enhanced the rate to a great extent for the first two substrates. This observation may provide an idea toward the rate determining step of the process. Notably, the third substrate, pyrocatechol, could not be oxidized by any of the two cata-lysts even with a base which might emphasize monodentate binding mode of the substrate. Each of the oxidation was monitored with the help of time dependent 1H-NMR spectroscopy. Conclusion:: A mechanistic pathway has been proposed. The spectra obtained in different cases help to compare the efficiency of the catalysts with or without base. In the absence of the catalysts, triethyl-amine alone cannot complete the conversion in the stipulated time, which may establish the effective-ness of the catalysts via the base-assisted mechanism.