THE ELECTROCHEMISTRY OF TRIBUTYLTIN AT MERCURY-ELECTRODES IN AQUEOUS-MEDIA

The electrochemical reduction of tributyltin (Bu3Sn+) at mercury elect rodes has been investigated in aqueous media with nitrate and chloride electrolytes using the techniques of cyclic voltammetry, differential pulse polarography, and differential pulse voltammetry. In contrast t o previous studies in mixed aqueous-organic media, the electrochemical processes were found to be surface confined. At low concentrations, c orresponding to less than monolayer coverage of the mercury electrode, the initial charge transfer process occurs after adsorption at approx imately -0.8 V vs. the saturated calomel electrode (SCE) and is essent ially reversible, the complete process being described by the reaction Bu3Sn+(bulk) --> Bu3Sn+(ads) + e- half arrow right over half arrow le ft Bu3Sn'(ads) At more negative potentials (approximately -1.3 V vs. S CE) a reversible tensammetric process is observed: Bu3Sn(ads) half arr ow right over half arrow left Bu3Sn(desorb) In concentrated chloride m edia this tensammetric process has a well-defined counterpart: Bu3Sn+( ads) half arrow right over half arrow left Bu3Sn+(desorb) at approxima tely -0.06 V vs. SCE, showing that strong adsorption takes place over almost the entire potential range available at mercury electrodes. At higher concentrations, corresponding to more than monolayer coverage o f the mercury electrode, the electrochemistry is more complex and addi tional processes are observed.