Reaction kinetics of the oxidation of o-phenylenediamine with ammonium persulfate

CHED 1022

Erik W. Hobbs, ehobbs2@washcoll.edu1, Edward G. Hohenstein, ed.hohenstein@gatech.edu2, and James R. Locker, rlocker2@washcoll.edu1. (1) Department of Chemistry, Washington College, 300 Washington Avenue, Chestertown, MD 21620, (2) School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400
The oxidation of o-phenylenediamine has been extensively studied. The principle product is often 2,3-diaminophenazine, but when oxidized with ammonium peroxysulfate in strong acid Iseminger et al. showed an additional product 3-aminophenaz-2-ol. In this work the rate of product formation is followed using a stopped-flow kinetics apparatus and UV-Vis spectrometry. A tentative mechanism is proposed and tested using a kinetic model based on numerical integration. In this mechanism o-aminophenol is produced during the course of the reaction and is involved in the production of 3-aminophenaz-2-ol. This hypothesis was tested by adding o-aminophenol to the initial reaction mixture and observing the relative rates of the formation of the two products. Iseminger et al. recovered the 2,3-diaminophenazine as the hydrochloride salt. Based on the NMR spectra Iseminger et al stated that the proton bridged the two amine nitrogens. Our data and molecular modeling calculation suggest that the protonation is on the ring nitrogens.