Benzoquinone imines. Part 15. Kinetics and mechanism of the hydrolysis and cyclization of 2-amino-N-(p-hydroxyphenyl)-p-benzoquinone di-imines in aqueous solution

2-Amino-N′-(p-hydroxyphenyl)-p-benzoquinone di-imines undergo hydrolysis at the azomethine bridge at pH <4, intramolecular cyclization to 2-amino-8-hydroxyphenazines at pH 6–10, and hydrolysis at the terminal imino-group at higher pH. Acid hydrolysis involves reaction of the dication with water forming p-aminophenol and 2-amino-p-benzoquinone monoimine. Phenazine formation occurs by intramolecular coupling of the 2-aminonitrogen of the zwitterion to the 2′-carbon atom, followed by oxidation. Alkaline hydrolysis involves attack by hydroxide ion on the zwitterion to give the corresponding 2-aminoindophenol.