The Mechanism of Formation of Phenosafranine Dyes

Abstract

The formation of phenosafranine dyes, from the oxidation of mixtures of p‐diamines and arylamines, is shown to be a seven‐step process. It entails oxidation of the p‐diamine to the p‐benzoquinonedi‐imine, which, as its conjugate acid, reacts with the arylamine to give a diarninodiphenylamine. Rapid oxidation of this gives an indamine that reacts, as its conjugate acid, with a second molecule of the arylamine to give a tetramino compound that is rapidly oxidised to the corresponding arylaminoindamine. The latter compound, in the form of its conjugate acid, undergoes intramolecular cyclisation, followed by rapid oxidation, to give the phenosafranine. In dilute solution (˜10‐4m), all but the four oxidation steps are slow and proceed at comparable rates, whereas, under preparative conditions, the arylamine addition and the intramolecular cyclisation are the slow steps.

Enzymatic Synthesis of Highly Electroactive Oligoanilines from a p-Aminodiphenylamine/Aniline Mixture with Anionic Vesicles as Templates

“…The fully reduced aniline trimer does not absorb in the visible range, but the in situ UV/vis/NIR spectra (Figure a) show a sharp band at 700 nm. A band at 700 nm is consistent with the formation of an oxidized radical cation form of the aniline trimer, as shown in Scheme . This form is still reactive (i) and may either combine with another trimer to form an aniline hexamer (ii) or convert into the aniline trimer in its reduced form.…”

“…A band at 700 nm is consistent with the formation of an oxidized radical cation form of the aniline trimer, as shown in Scheme 5. 50 This form is still reactive (i) and may either combine with another trimer to form an aniline hexamer (ii) or convert into the aniline trimer in its reduced form. The slow electrophilic aromatic addition between two aniline trimers, case (i), may yield a linear aniline hexamer.…”

Azine Dyes

“…In an investigation of the reaction kinetics, CORBETT [3] was able to establish the following mechanism of formation of phenosafranine 9 by the joint oxidation of p-phenylenediamine and aniline:…”