Benzoquinone imines. Part 17. Kinetics and mechanism of the hydrolysis and cyclization of 2-aminoindophenols in aqueous solution

Abstract

2-Aminoindophenols undergo hydrolysis at the azomethine bridge at pH < 5 and intramolecular cyclization, to give 2,8-dihydroxyphenazines, at pH > 8. At intermediate pH, decomposition occurs to give products which have not been identified. Phenazine formation involves the indophenol anion and hydrolysis the monocation. The neutral species is relatively stable. The instability of the anion towards oxidizing agents, including hydrogen peroxide formed in the air oxidation of the dihydrophenazine, mitigates against the use of the reaction for preparative purposes.