Electrosynthesis

Lore & Background

In electrosynthesis, reactants are activated in-situ using energy from an applied electric field. The basic setup includes a galvanic cell, a potentiostat, and two electrodes. Typical solvent and electrolyte combinations minimize electrical resistance. Protic conditions often use alcohol-water or dioxane-water mixtures with a soluble salt, acid, or base. Aprotic conditions often use organic solvents such as acetonitrile or dichloromethane with electrolytes like lithium perchlorate or tetrabutylammonium salts. The choice of electrodes—such as graphite, lead, platinum, magnesium, mercury, stainless steel, or reticulated vitreous carbon—can be decisive. Cell designs may be undivided or divided, with divided cells using a semiporous membrane to permit ion diffusion while restricting product and reactant flow.

Reader's Guide

Electrosynthesis is significant for its potential to improve selectivity, yield, energy efficiency, waste reduction, safety, and atom economy compared to traditional stoichiometric reagents, aligning with principles of Green Chemistry. However, it may still require hazardous solvents, electrolytes, conductivity aids, or sacrificial reagents. Industrial applications include the production of adiponitrile from acrylonitrile, propiolic acid from propargyl alcohol, and perfluorinated compounds via electrofluorination in liquid HF. The method also has potential for wastewater treatment through electrooxidation. Reactions are classified as anodic oxidations (e.g., Kolbe electrolysis, Shono oxidation, conversion of alcohols to carboxylic acids) and cathodic reductions (e.g., hydrodimerization, reduction of arenes, carboxylation). Current efficiency is a key metric, and constant potential is more efficient than constant current due to side reactions at fixed rates.

Did You Know?

• The Kolbe electrolysis involves decarboxylation of two carboxylic acids and coupling of the remaining radicals.
• Adiponitrile is prepared industrially by cathodic hydrodimerization of two equivalents of acrylonitrile.
• Electrofluorination uses liquid HF at 5–6 V with Ni anodes to produce perfluorinated derivatives of amines, alcohols, carboxylic acids, and sulfonic acids.
• An electrochemical carboxylation of para-isobutyl benzyl chloride to Ibuprofen is promoted under supercritical carbon dioxide.