Acid-catalysed degradation of the organomercury intermediates of pentafluorophenylmercury bromide reduction near a mercury electrode

Electrode reactions and electroanalysis of organomercury compounds

“…26). It is known 132 that bromodemercuration often proceeded at high rates even at room temperature (probably, via unstable intermediates of the radical nature, as was observed in other publications 121,143,144,178 ).…”

“…119,120 Scheme 1 was proposed to describe the mechanism of OMC electroreduction at a mercury electrode in the general form. 121 However, even this generalized scheme does not reflect to the full extent the details of the ER mechanism for different OMC. In particular, it does not consider the effects of the adsorption of components of the electrochemical system and also of heterogeneous equilibria such as (6) in Scheme 1 on the surface and in the bulk solution.…”

“…179 The next aspect of this problem, namely, the proton donor-induced degradation of mercury-containing intermediates was discussed. 121 It was found 122 that the addition of even small amounts of acids (3 < pH < 6) to solutions of C 6 F 5 HgBr resulted, in place of the expected blockage removal, in the disappearance (Fig. 11, curve 4) delay corresponding to the ER of the near-electrode condensed perfluorodiphenylmercury phase, while the length of the delay of monolayer reduction no longer depended on either i (curve 3) or the polarization time t p (Fig.…”

“…For low AcOH concentrations (0.9 mol litre 71 NaOAc, pH 4.4 ± 5.5), the delay corresponding to the ER of this compound [see Eqn (7), Scheme 1], which was the only delay at high i, remained virtually unchanged, 121 whereas the delay corresponding to the ER with the preliminary formation of organic calomel' [RHg ads ] n (see Section III and Ref. 113) disappeared.…”

“…26 For example, storage of MeHgCl (5610 74 mol litre 71 ) in HCl solution with pH 1 for a week did not change its polarogram. 26,121 As a rule, protolysis of OMC is a lengthy procedure carried out under sufficiently drastic conditions (elevated temperatures, high acid concentrations). 26 For the described 121 systems, the protolytic effect was observed even in weakly acidic media (pH 4 4.8 ± 5.5) at room temperatures; after the solutions of pentafluorophenylmercuric bromide and bis(phenylethynyl)mercury were neutralized with an alkali in the electrochemical cell, the original state was completely recovered, which pointed to the absence of protolysis of these compounds.…”