The electrochemistry of monobutyltin and mixtures of butyltin compounds at mercury electrodes in aqueous media

The electrochemical reduction of dilute aqueous solutions of monobutyltin containing nitrate and chloride electrolytes has been examined at mercury electrodes using the techniques of direct current polarography, cyclic voltammetry, differential pulse polarography and differential pulse voltammetry. In the present study, the processes were found to be much more reversible than reported in earlier investigations where more concentrated solutions were examined using direct current techniques. The primary charge transfer process is a reversible three-electron reduction step which occurs at approximately −0.5 V vs. Ag/AgCl (3 M KCl) and corresponds to the reaction BuSn3+ + 3e− BuSn At slightly more negative potentials, the reduction process at a stationary mercury electrode, but not significantly at a dropping mercury electrode, is inhibited by adsorption and polymerisation of the reaction product. However, at considerably more negative potentials, the exact value of which is strongly dependent on the solution conditions, product adsorption and electrode blockage by film formation ceases to occur. The electrochemistry of mixtures of monobutyltin, dibutyltin and tributyltin also has been examined. Interactions between the electrode processes implies that the direct and simultaneous voltammetric determination of these forms of butyltin compounds in aqueous samples is extremely problematic.