Electrolysis Using Solid-Supported Bases

Tajima and co-workers have developed a novel environmentally friendly electrolytic system using solid-supported bases and protic organic solvents such as methanol [24], This method permits electrolysis without an intentionally added supporting electrolyte. Solid-supported bases are not oxidized at the electrode surface because electron transfer between two solids is, in principle, very difficult [25], Therefore, protons generated by the reaction of a solid-supported base and a protic solvent may serve as carriers of electronic charge. After the electrolysis, the solid-supported base can be easily separated by filtration and can be re-used. 

Anodic a-methoxylation of phenyl 2,2,2-trifluoroethyl sulfide was carried out using various solid-supported bases as shown in Equation 12.6. Polystyrene and silica -gel are suitable as the solid support for an organic base such as piperidine. It is noteworthy that anodic methoxylation was successfully carried out even after 10 recycles of the solid-supported base. The method has also been successfully applied to electrochemical acetoxylation in acetic add/acetonitrile. 

The anodic oxidation of carboxylic acids has also been carried out using a solid-supported base in methanol. Non-Kolbe-type electrolysis takes place to give the corresponding methoxylated product (Equation 12.7). The acid-base reaction between a carboxylic acid and a solid-supported base seems to reduce the cell voltage and makes the electrochemical reaction possible. Kolbe-type carbon-carbon coupling using aliphatic and benzylic carboxylic acids has also been accomplished using this method [26]. Based on a similar concept, anodic fluorination by an alkali metal 

---