On the Electrochemical-Behavior of Pyrylium Ions at the Mercury-Electrode. II. Aromatically Substituted Ions in Acetonitrile

Abstract

The electrochemical behaviour of the 2,4,6-triphenylpyrylium ( tpp ⁺) and 7-phenyl-5,6,8,9-tetrahydrodibenzo[ c,h ] xanthylium (thx⁺) ions in acetonitrile in the presence of 0.1 M tetrabutylammonium perchlorate is reported. The reduction of both ions proceeds by two, one-electron steps. The initial product of the first reduction is the corresponding radical, which may dimerize to give isomeric bipyrans in the case of tpp + or a phenyl-phenyl or phenyl- pyranyl dimer in the case of thx⁺. The corresponding anions are the initial products of the second reduction step. The tpp ^- anion reacts with tpp ⁺ to give the bipyran while the thx^- anions appear to undergo polymerization reactions with thx⁺. Both tpp ⁺ and thx⁺ and their reduction products are adsorbed at the mercury electrode. In the adsorbed state thx⁺ forms one of two surface phases depending on the potential, one with the molecules in a flat orientation and the other, a condensed phase, with vertically oriented molecules. Perchlorate ions are considered to be co-adsorbed with the cations.