โ Scribed by B. Fleet; R.D. Jee
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The polarography of organo-mercury(II) compounds of the type RHgX has been widely studied due to their importance as pharmaceuticals and fungicides. Many 0 f the papers published are analytical in nature with little or no mechanistic details 1 -14. Although the mechanism of reduction has been extensively studied 15-33 during the past twenty years, the literature still contains many conflicting statements concerning reversibility and adsorption effects.
Olefins react with mercury(II) acetate in methanol to give compounds of the type RCH(OMe)-CH(HgOAc)R', according to the equation:
Although the chemical properties of these compounds have been comprehensively reviewed by Chatt 34, there are virtually no studies of the mechanism of the electroreduction. As a consequence the present investigation was carried out.
Electrochemical reduction of organo-mercury(II) compounds can be traced to the work of Kraus 35, who electrolysed liquid ammonia solutions of alkyl mercury-(II) halides and found that the product RHg" dimerized to RzHg at room temperature. Sullam 36 in an investigation of ethene mercury(II) salts observed that the organic mercury differed polarographically from that of inorganic mercury. In the work of Costa 15 which has been largely overlooked, various alkyl mercury(II) salts were examined. Two polarographic waves were observed, which from the wave shape were concluded to be irreversible, R-Hg + +e ~ R-Hg" R-Hg'+H + +e ~ R-H+Hg Vojir 16'17 and Benesch and Benesch 18'~9 studied the reduction of phenyl mercury(II) salts. The little quoted work of Vojir observed the first wave to be reversible from a.c. oscillopolarographic measurements. Benesch and Benesch, however, whose work is generally quoted in analytical papers which refer to the reduction mechanism, considered the first wave irreversible as a consequence of its shape and Eยฝ-pH dependence above pH 7. The half-wave potential of the second wave was found to show a marked pH dependence up to approximately pH 8, though it was independent ofpH above this value. Hush and Oldham z4 studied a large range of compounds and from the wave shape concluded the first wave to be reversible ; the wave was also independent of pH. In very alkaline solutions an values indicated reversibility for the second wave. Butin et al. z8 point out that the Heyrovsk3~-Ilkovic
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