An Investigation of Electron Transfer Reactions between Aromatic and Quinoid Systems
作者:M. Goez、W. Jaenicke、U. Nickel
DOI:10.1002/bbpc.198800110
日期:1988.4
AbstractA classical organic redox reaction is the conversion of an aromatic compound from its reduced form R to a semioxidized state S, and further to a totally oxidized (quinoid) species T. Complex redox systems are present in a reaction of quinoid and aromatic forms derived from different parent compounds. In this case, the exchange of one or two electrons in one step between T and R can be distinguished experimentally. These reactions were investigated in a stopped‐flow apparatus with optical detection. In the system N,N,N′,N′‐tetramethyl‐para‐phenylene‐diamine/N,N‐dimethyl‐para‐phenylene‐diamine the rate constants for all elementary reactions have been determined. Protonated, and unprotonated R were found to be reactive. In this system, as well as the others considered, no direct transfer of two electrons between T1 and R2 takes place. The essential steps of the mechanism have to be seen in a mixed symproportionation yielding S1 and S2, and a subsequent fast oxidation of S2 by surplus starting material T1. As a generalization, a tangent criterion has been derived to distinguish between one‐ and two‐electron steps in such mixed redox systems.