Multiphase Methods in Organic Electrosynthesis

Abstract

With water providing a highly favoured solution environment for industrial processes (and in biological processes), it is interesting to develop water-based electrolysis processes for the synthesis and conversion of organic and biomass-based molecules. Molecules with low solubility in aqueous media can be dispersed/solubilised (i) by physical dispersion tools (by milling, by power ultrasound, or by high shear ultra-turrax processing), (ii) in some cases by pressurising/super-saturation (e.g. for gases), (iii) by adding co-solvents or "carriers" such as chremophor EL, or (iv) by adding surfactants to generate micelles, microemulsions, and/or stabilised biphasic conditions. This review examines and compares methodologies to bring the dispersed or multi-phase system into contact with an electrode. Both the microscopic process based on the individual particle impact as well as the overall electro-organic transformation are of interest. Distinct mechanistic cases for multi-phase redox processes are considered.Most traditional electroorganic transformations are performed in homogeneous solution with reagents, products, electrolyte, and possibly mediators or redox catalysts all in the same (usually organic) solution phase. This may lead to challenges in the product separation step and in the re-use of solvents and electrolytes. When exploiting aqueous electrolyte media, reagents and products (or even electrolyte) may be present as microdroplets or nanoparticles. Redox transformations then occur during interfacial "collisions" under multiphase conditions or

Mapping Solvent Entrapment in Multiphase Systems by Electrogenerated Chemiluminescence

“…For example, while water-in-oil emulsion systems have been extensively studied, the dynamic interaction between suspended water droplets and charged surfaces (i.e., electrodes) requires more rigorous evaluation. A detailed understanding of the various phase boundaries formed by a continuous liquid oil phase, a dispersed liquid water phase, and a solid metallic phase is paramount to optimize multiphase electrosynthetic reactions, which exploit various phase properties. − Of particular interest are three-phase boundaries, which often facilitate unique chemical processes (e.g., ion transfer). , Optical techniques are well suited to visualize the morphology of water droplets adsorbed to an electrode surface immersed in an oil phase but lack the ability to visualize the water|electrode two-phase boundary and the oil|water|electrode three-phase boundary. In order to enhance the contrast at the two-phase boundary, we previously coupled droplet-confined electrogenerated chemiluminescence (ECL) to optical microscopy, a technique that permitted quantification of the droplet contact area .…”

Bridging Lab and Industry with Flow Electrochemistry

“…Conductivity is easily achieved for electrolysis under aqueous conditions; however, organic reactions are not usually feasible in water. In some cases where reactions can tolerate water, a practical alternative is the use of a biphasic or emulsion aqueous/ organic mixtures in which organic droplets are dispersed in an aqueous media (Marken and Wadhawan, 2019). Mostly, organic electrosyntheses are done in organic solvents containing supporting electrolytes that offer enhanced conductivity.…”

Single-entity electrochemistry at confined sensing interfaces

“…In a similar fashion, CEPhT reactions are also observed during electrodeposition, where the redox species transfers from a liquid phase to a solid phase while being oxidized or reduced. Furthermore, CEPhT reactions are essential in multiphase organic electrosynthesis, [220] which has been shown to be an environmentally friendly, economical, and safe alternative to homogeneous organic electrosynthesis. Multiphase electrosynthesis relies on the use of three immiscible phases, such as an electrode placed in an oil-in-water emulsion.…”