Zum Mechanismus der Induktionsperioden bei der Oxidation N‐substituierter p‐Phenylendiamine

The appearance of induction periods when oxidizing p‐phenylene diamines may be due to different reasons. In acidified aqueous solution distinct induction periods are observed for the formation of semiquinonediimine as well as quinonediimine with nearly all oxidizing agents employed. In this case primary oxidation is very slow because of the low concentration of oxidizable unprotonated p‐phenylenediamine. After the formation of some semiquinonediimine which is unprotonated, however, its subsequent oxidation accelerates the reaction in an autocatalytic way. Under different conditions of reaction either formation of quinonediimine or semiquinonediimine is retarded. Certain foreign substances give rise to a significant shortening or prolongation of the induction period, although the actual oxidation reaction is not noticeably. The different mechanisms are discussed and the reaction rates for the autocatalytic reaction are presented for some redox systems.