G. Zotti et al., ANION-ASSISTED ANODIC COUPLING OF 2,2'-BIPYRROLE - ROLE OF TOSYLATE ANION IN THE ELECTROCHEMICAL SYNTHESIS OF POLYPYRROLE, Chemistry of materials, 7(8), 1995, pp. 1464-1468
Cyclovoltammetric analysis has shown that anodic coupling of 2,2'-bipy
rrole in acetonitrile is influenced by the electron-donor properties o
f the anion of the supporting electrolyte. 2,2'-Bipyrrole oxidation in
the presence of poor electron-donor anions (ClO4-, PF6-, BF4-, CF3SO3
-) occurs in a one-electron process at a potential independent of the
anion, yielding the dimer whereas with more electron-donor anions (tos
ylate, benzenesulfonate, methanesulfonate, camphorsulfonate, chloride,
and nitrate) the oxidation process is shifted to lower potentials acc
ording to the anion type and concentration, requires 2.5 electrons/bip
yrrole unit and results in polypyrrole formation. The results are expl
ained by ion pairing and hydrogen bonding of the electron-rich anion w
ith the initially produced radical cation to form a highly reactive ra
dical species. As a consequence, the well-known favorable action of to
sylate in promoting polypyrrole formation may be satisfactorily accoun
ted for by a chemical homogeneous process rather than by morphological
factors.