One-Electron Redox Reactions Involving Sulfite Ions and Aromatic Amines

Article abstract of DOI:10.1021/j100255a049

The one-electron oxidation of aromatic amines by the SO3^- radical and of the sulfite and bisulfite ions by aromatic amine radical cations has been investigated. p-Phenylenediamine (PDA) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) were oxidized by SO3^- with rate constant of 5.0 x 1E7 and 5.2 x 1E8 M^-1 s^-1, respectively, in basic solutions.Protonations of the amine reduced the rates considerably (k = 4.2 x 1E6 M^-1 s^-1 for PDA at pH 5.25; k = 8.2 x 1E6 M^-1 s^-1 for TMPD at pH 4.5).Witn aniline and N,N-dimethylaniline (DMA), the reverse reaction was observed.DMA⁺ radical reacted with SO3^2- with k = 9.9 x 1E8 M^-1 s^-1 and with HSO3^- k < 5 x 1E5 M^-1 s^-1.Aniline radical cation also oxidized SO3^2- rapidly (k = 4 x 1E9 M^-1 s^-1) and HSO3^- less rapidly (k = 4.8 x1E6 M^-1 s^-1).The aniline neutral radical reacted too slowly to be measured with either.A secondary product was observed in acid solution of TMPD with an absorption maximum at 455 nm.This was ascribed to a reaction between the SO3^- and TMPD⁺ radicals.