Kinetics and mechanism of the acid deamination of N-substituted quinone di-imines measured with a multi-mixing, stopped-flow technique
- 1 January 1978
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 11,p. 1188-1193
- https://doi.org/10.1039/p29780001188
Abstract
A stopped flow apparatus with six syringes and five mixing chambers is described which allows several stoppages at given intervals. Seven partially ring methylated, N-substituted p-phenylenediamines (R) were oxidised by iodine or permanganate. The deamination of the quinone di-imines (T+) formed was studied in the pH range 1–10 by means of a colour coupling process after different intervals or from the extinction of the radical intermediate as a function of time. T+ is in a fast equilibrium with its protonated form TH2+. Deamination is initiated by nucleophilic attack on the most positively charged carbon atom of the ring. Therefore, in acid solution TH2+ is deaminated by H2O giving the substituted quinone monoimine and in alkaline solution T+ is deaminated by OH–, giving the respective unsubstituted quinone monoimine. The equilibria and the rate constants were measured at 25 °C. The stability maximum of T+ is at pH 6 whereas the N-substituted quinone monoimines are stable at pH – and with H2O were found, giving in both cases p-benzoquinoneKeywords
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