Benzoquinone imines. Part 13. Reactions of N-methylated 2-aminoindamines in aqueous solution

Abstract

N-Methylated 2-aminoindamines (2-amino-N-(4-aminophenyl)-p-benzoquinone di-imines) undergo hydrolysis at the azomethine bridge at pH < 4, intramolecular cyclization to diaminophenazines at pH 4–9.5, and hydrolysis of the terminal imino-group at high pH. The effect of N-methylation of either amino- or imino-group on the rate of these reactions is consistent with the proposed mechanisms. Acid hydrolysis involves reaction of the dication with a hydroxonium ion and with water, cyclization involves an intramolecular coupling of the 2-aminonitrogen of the monocation, to the 2-carbon atom, followed by oxidation, and alkaline hydrolysis involves reaction of a hydroxide ion with the monocation. The N⁴N⁴-dimethylindaminium ions form a neutral species at pH > 11 by loss of a proton from the tautomeric form 4-dimethylamino-N¹-(4-aminophenyl)-o-benzoquinone di-imine. 2-Dimethylaminoindamines undergo rapid intramolecular cyclization to give the colourless 2,8-diamino-10.10 dimethyl-5,10-dihydrophenazinium ion. This is slowly converted into a 10-methylphenazinium salt, a methyl group being eliminated as methanol.