The Reaction Mechanism of p‐Toluenediamine Anodic Oxidation: An In Situ ESR‐UV/Vis/NIR Spectroelectrochemical Study

Abstract

In situ ESR-UV/Vis spectroelectrochemistry is applied to obtain new insights into the intermediates and reaction products of the anodic oxidation of p-toluenediamine in aqueous solution at different pH values. A strong pH dependence of the stability of the cation radical is found. While the absence of a stable radical was proved by ESR spectroscopy at pH 2 and 10, this radical is detected at medium pH values and assigned to the semiquinonediimine structure. The UV/Vis absorption of the radical is observed at these pH values as well. The p-toluenediimine intermediate and the trimeric reaction product were followed during the electrode reaction by UV/Vis spectroscopy at all pH values.

Oxidative transformation processes and products of para-phenylenediamine (PPD) and para-toluenediamine (PTD)—a review

“…In the last years, only Goux et al made efforts in this direction [47]. The spectroelectrochemical oxidation of PTD on a platinum electrode at neutral pH resulted in the formation of a dimer proven by UV/VIS and EPR spectra ( Table 3).…”

“…Goux et al determined an analogous product of PTD by spectroelectrochemical methods (cyclic voltammetry-UV/VIS spectroscopy) in the pH range of 4 to 7 (Table 3) [47]. The structural evidence is merely based on the comparison of the obtained UV spectra with that of a BB standard.…”

“…Michaelis et al vaguely characterized it with UV-VIS spectroscopy (Table 5) [41]. Electrochemical oxidation combined with simultaneous UV-VIS and EPR spectroscopic analysis led to an improved characterization of the chemical species [47].…”

“…Furthermore, the diimine formation was indirectly ascertained by the determination of an adduct with a mass increment of 107 amu being formed by in situ electrochemical transformation of PPD in the presence of glutathione and cysteine [25]. The corresponding toluquinone diimine of PTD (Table 3) was UV/VIS spectroscopically determined in aqueous solution at pH 4 and 7 after electrochemical PTD oxidation [47]. The absorption maxima of 252 and 326 nm at pH 2 are comparable with that of the corresponding PPDdiimine.…”

Construction and Efficient Radical Cation Stabilization of Cyclodextrin/Aniline Polypseudorotaxane and Its Conjugate with Carbon Nanotubes

“…It is well known that there existed numerous radical cations in the emeraldine state, i.e., the conductive doped form, of PANI, and the stabilization of these radical cations is very important to the stability and conductivity of PANI. [10] In previous reports, PANI could be stabilized by pH modulate, [11] propylthiosulfonated modification, [12] and complexation with DNA. [13] Recently, Anderson and coworkers [14] reported the radical cation stabilization in a CB [7]/oligoaniline rotaxane.…”