Electrocatalytic reduction of alkyl iodides in tetrahydrofuran at silver electrodes

Abstract

Recent interest in the electrocatalytic activity of silver towards the reduction of alkyl iodides has led us to investigate whether the effect is observed in tetrahydrofuran (THF) at room temperature. Using platinum electrodes in THF for the reduction of alkyl halides at 298 K has been hampered by the solvent window, which 'obscures' the voltammetric signals of interest. In order to overcome these problems, voltammetry has been performed at low temperature and was shown to extend the voltammetric window, leading to accurate electrochemical analyses and even novel changes in mechanism(s) of the reactive species following electron-transfer (ET). Herein, it is shown that for a primary and tertiary alkyl iodide in THF, electroreduction at silver leads to a significant shift in the reduction potential to more positive values compared to platinum. In addition, following reduction, a characteristic series of oxidation peaks are observed and are shown to be due to the specific activity of iodide ions towards silver following reductive cleavage of the parent alkyl iodide. This characteristic feature is not observed with other halide ions: bromide and chloride. Preparative electrolyses at controlled-potential have suggested that the reduction of the above alkyl iodides is a one-electron concerted process. The 'free' iodide ions act as a monitor of reaction progression, and the carbon-centred radical either dimerises and/or abstracts a hydrogen atom from the electrolyte/solvent; 1-iodoadamantane giving percentage yields of 58% adamantane and 39% 1,1'-biadamantane, the primary alkyl iodide, prepared in-house, giving 67% R-H and 25% R-R.

Cryo-electrochemistry in tetrahydrofuran: The regioselective electrochemical reduction of a phenyl sulfone: Fast-scan cyclic voltammetry investigations

“…Experimental data is fitted by using ORIGIN 6.0e. The use of this technique to elucidate both the parameters D and n has been applied in the case of a phenyl thioether [4].…”

“…Analyses at room temperature showed the 'plateau' current having contributions coming from solvent electroactivity. In a previous paper, we have recently highlighted the benefit of using low temperatures to investigate electroreductions in THF [4]. Accordingly, the microdisc voltammetry of RSO 2 Ph at lower temperatures was investigated.…”

“…Before carrying out electrochemical experiments, the microdisc radius was electrochemically calibrated using a literature methodology [38]. A Fc=Fc þ PF À 6 reference electrode was developed for use in THF at low temperature and is described elsewhere [4,37]. Tetra-n-butylammonium perchlorate was added to freshly distilled THF with all experiments undertaken in an acetone|dry ice bath thermostatted at 196 ± 1 K. Intermediate temperatures were achieved using an acetone|dry ice bath by monitoring the temperature with a handheld temperature probe TME 2030 (TM Electronics (UK) Ltd.).…”

“…New pathways and alternative bond-dissociation steps may be observed at low temperatures. We have already shown that the cathodic potential window in THF offered at low temperatures is extended and allows chronoamperometric and voltammetric analyses of waves and peaks to be better resolved from the solvent window, thus facilitating accurate step potentials to well-defined steady-state current plateaus in potential-step experiments and voltammetric sweeps to be reversed without significant scanning into the solventdecomposition window [4]. Additional benefits maybe realised by using electrochemical techniques such as fast-scan cyclic voltammetry [5][6][7][8] at low temperatures in organic solvents such as the work carried out by Evans et al [9] In particular, electrogenerated species with fast follow-up chemical reactions after initial electron transfer can be probed by using fast-scan techniques allowing kinetic data to be obtained.…”

Novel and efficient electrochemical way for silver nanoparticles deposition onto solid conductors: a new concept of metal-silver cathodes

“…The growing interest for silver electrodes [16][17][18][19][20][21] and their catalytic possibilities prompted us to consider new modified silver interfaces in particular by the use both of palladium metal and a silver-palladium alloy [22][23][24][25]. As a complement to these recent discoveries, it is here reported a new and facile mode for deposition at solid conducting surfaces of extremely small silver particles based on the reaction of alkyl iodides RI with silver and silverpalladium alloy.…”