Electrolysis electroorganic reactions

The third contribution deals with an rather old synthetic electroorganic reaction, Kolbe-Electrolysis. However, recently this reaction has found so many interesting and important new applications, for example in the synthesis of natmully products or the generation of versatile, even enatiomerically pure, synthetic building blocks, that it was nec sary to cover these new developments in a review. As these reactions are usually very easy to perform without expensive equipment, it is hoped that further applications in many laboratories will be initiated by this article. 

Another important classification of electroorganic reactions is obtained by dividing them into those in which the substrate undergoes direct electron transfer with the electrode (direct electrolysis) and those in which an additional compound (redox catalyst, mediator) transfers the redox equivalents between the substrate and the electrode (indirect electrolysis). 

In general, controlled-current electrolyses need less expensive equipment. Only a controlled-current source in combination with a coulomb integrator is necessary. Therefore, in industry, electroorganic reactions are always performed at a fixed current density. In the laboratory, it is advisable to start with controlled-potential electrolyses using a potentiostat and a three-electrode electrolysis cell (Fig. 22.8). In this way, the reaction can be controlled at the redox potential of the substrate determined analytically, and the selectivity of the process can be studied at different potentials. After determination of the selectivity controlling factors, it is usually possible to change over to current control by proper selection of the current density and the concentration of the substrate. Using a continuous process, the concentration can be fixed at the desired value. Thus, selectivity can also be obtained under these conditions. 

The supporting electrolyte is essential for the electroorganic reaction. The foUowing points are important for the selection of the supporting electrolyte (i) solubility to the solvent commonly used for electrolysis (ii) electrochemical stability (iii) interaction with reaction inteimediate and (iv) relative difficulty of preparation. 

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