A microfluidic double channel device is employed to study reactions at flowing liquid–liquid junctions in contact with a boron-doped diamond (BDD) working electrode. The rectangular flow cell is calibrated for both single-phase liquid flow and biphasic liquid–liquid flow for the case of (i) the immiscible N-octyl-2-pyrrolidone (NOP)–aqueous electrolyte system and (ii) the immiscible acetonitrile–aqueous electrolyte system. The influence of flow speed and liquid viscosity on the position of the phase boundary and mass transport-controlled limiting currents are examined. In contrast to the NOP–aqueous electrolyte case, the acetonitrile–aqueous electrolyte system is shown to behave close to ideal without ‘undercutting’ of the organic phase under the aqueous phase. The limiting current for three-phase boundary reactions is only weakly dependent on flow rate but directly proportional to the concentration and the diffusion coefficient in the organic phase. Acetonitrile as a commonly employed synthetic solvent is shown here to allow effective three-phase boundary processes to occur due to a lower viscosity enabling faster diffusion. N-butylferrocene is shown to be oxidised at the acetonitrile–aqueous electrolyte interface about 12 times faster when compared with the same process at the NOP–aqueous electrolyte interface. Conditions suitable for clean two-phase electrosynthetic processes without intentionally added supporting electrolyte in the organic phase are proposed
The first reported use of benzeneperseleninic acid as a catalytic mediator for oxaziridinium ion catalysed epoxidation is described, providing reaction rates and ee values (up to 85%) similar to those reported when using oxone as the stoichiometric oxidant. A dual catalytic cycle is proposed, in which diphenyl diselenide is initially converted into the perseleninic acid, which in turn oxidises an iminium ion to the corresponding oxaziridinium species, thus facilitating asymmetric oxygen transfer to an alkene.
A highly selective catalytic oxidation system has been developed for the conversion of sulfides into the corresponding sulfoxides using urea-hydrogen peroxide as stoichiometric oxidant in the presence of a catalytic quantity of diphenyl diselenide.
Oxidation is one of the most important types of transformation in chemistry, and practical mild oxidation without added reagents or solvents has been a long-standing challenge. We have developed a highly practical solvent-free (biphasic) electrochemically driven oxidation system for the selective conversion of sulfides to the corresponding sulfoxides, and alkenes to the corresponding epoxides, in a very simple reactor system. Excellent yields are obtained for a variety of substrates, and neither over-oxidation to sulfone nor formation of diol by-products from alkene oxidation is observed. This simple system has excellent potential for scale-up, requires no storing or transport of stoichiometric oxidants, no heavy metals, and can be carried out with just water, sodium carbonate, hydrochloric acid, and an applied potential in a single cell. The electrolyte solution can be recycled and reused with no loss in activity
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