The primary forces in chemistry are the electrostatic attractions between electrons and nuclei. For this reason, electrochemistry synthesis is gaining in popularity, since it inherently addresses the ways in which scientists can deal with molecules.1
The term electrochemistry refers to the chemical changes where electricity is the driving force by passage of an electric current and production of electrical energy by chemical reactions which leads to addition or removal of electrons.2
Electrochemistry has a very useful application as a non-conventional energy source for activation of reactions in suitable solvents. It has gained attention over the usual homogeneous and heterogeneous reactions due to its special attributes in chemical processes like increased reaction rates, better conversion, selectivity, better atom economy and eco-friendly advantages. The electrochemical reactions do not require the use of oxidizing reagents and can be performed at ordinary room temperature.3
The door into electrochemistry opened in 1834, when Faraday described the anodic conversion of acetate anions to CO2 . Later on, Kolbe discovered the electrolysis of valeric acid to produce hydrocarbon.4 The slow upswing of electrochemistry is due to the lack of standardization in electrochemical equipment, with most of the “in-house/homemade setup” leading non-reproducibility in results, along with a limited number of reported notable transformations. Over the last few years, a significant amount of complex organic chemistry transformations has been reported from scientists at various renowned labs. Quite often, multiple chemical transformations occur under the electrochemical environments. These electrochemical transformations are considered to be clean, non-polluting and atom economic and provide a powerful tool for the late-stage functionalization (LSF) of many complex molecules by construction or divergence of novel molecules allowing the rapid synthesis of large compound libraries.5
Electrochemistry provides a gentle yet potent method for selectively catalyzing oxidative or reductive reactions, utilizing electrons as the primary agents, thus bypassing the need for harsh chemical reagents. This approach not only boosts atom efficiency but also often eliminates the requirement for additional steps like protection/ deprotection protocols.
Within the realm of electrochemistry, numerous pathways have been unveiled that facilitate the creation of novel bonds, which might be exceptionally challenging or even unachievable using conventional synthetic approaches. Recent reviews have underscored instances of bond formations, including the establishment of C(sp3)−C(sp3) and C(sp3)−C(sp2) linkages, all made possible through electrochemical processes,6 thereby highlighting promising avenues for further investigation. Electrochemistry stands out as a superior method for bond formation involving highly reactive substrates, where stoichiometric quantities of reagents are rendered unnecessary (given that electrons serve as the reagent), thus promoting a more environmentally sustainable methodology.
Electrochemical synthesis commonly describes the anodic oxidation and cathodic reduction. In anodic oxidation, an electron is eliminated from the molecule thus forming a highly reactive nucleophile intermediate whereas in cathodic reduction, an electron is added to the molecule as an electrophile.7 Generally, electrochemical synthesis holds moderate reaction conditions like solvent choice, operation voltage, temperature, and air humidity along with high functional group tolerance.8
The choice of solvent is crucial in electrochemical reactions, affecting factors such as stabilizing intermediates and promoting counter reactions. Aprotic solvents like THF, DCM, MeCN, DMSO, DMA & DMF and protic solvents such as hexafluoro isopropanol (HFIP), MeOH, EtOH, & trifluoroethanol are commonly used. Polar solvents are preferred for their lower resistance and better electrolyte dissolution. The "solvent window" defines the potential range over which a solvent remains stable against oxidation and reduction.
Similarly, electrolytes play an important role to decrease resistance and lower potential in electrochemical reactions. Tetraalkylammonium salts, particularly Tetrabutylammonium TBA salts, are commonly used due to their solubility. Inert counter ions like PF6 − and BF4 − are preferred to avoid undesired redox processes.
In addition to this, electrodes made up of any conducting material can be used. Based on the inertness of electrode material, size and shape, substantial differences in reaction outcome can be observed as the reactions take place on the electrode surface hence the surface area is an important factor. Foams or meshes have a higher surface area than plates or rods, and can therefore be beneficial for a reaction by increasing the reaction rate.2
Electrochemical synthesis can be performed in both undivided and divided cells. In an undivided electrochemical cell, the cathode and anode are kept in the same chamber. This setup is easy to carry out, as no sophisticated glassware/reactor is needed. In addition, the distance between the two electrodes can be easily adjusted, and ionic species can move freely between the electrodes. Whereas in a divided electrochemical cell, the cathode and anode are kept in different chambers which are separated by an ion-permeable membrane or salt bridge. This will require the special membrane or salt bridge and a reaction vessel of complicated design.
