On the Electrochemical Behavior of Pyrylium Ions at the Mercury-Electrode. III. Adsorption Behavior at the Aqueous-Mercury Interface

The adsorption behaviour of four pyrylium ions-2,4,6-trimethylpyrylium, 2,4,6-tri-t- butylpyrylium , 2,4,6-triphenylpyrylium and 7-phenyl-5,6,8,9-tetrahydrodibenzo[ c,h ] xanthylium -at the mercury-aqueous 0.5 M sulfuric acid interface is reported. The 2,4,6-trimethylpyrylium ion shows little tendency to adsorb at the mercury interface even at concentrations approaching saturated solution. The tri-t- butylpyrylium ion is adsorbed in a vertical orientation on a positively charged electrode, while on a negatively charged electrode it exhibits two position adsorption- initially flat then reorienting to vertical at higher concentrations. Triphenylpyrylium ions form an adsorbed layer of vertically oriented ions which approaches monolayer coverage at potentials just prior to its reduction at -0.68 V. The product of the reduction inhibits the reduction of the parent ion. The xanthylium ion behaves in a similar manner to the tri-t-butyl ion but the conclusions are tentative due to the limited reliability of the data as a consequence of the low solubility of this ion in water.