ANION-ASSISTED ANODIC COUPLING OF 2,2'-BIPYRROLE - ROLE OF TOSYLATE ANION IN THE ELECTROCHEMICAL SYNTHESIS OF POLYPYRROLE

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.