Kolbe electrolysis Subject

The yield and selectivity of Kolbe electrolysis is determined by the reaction conditions and the structure of the carboxylate. The latter subject is treated in chaps 3, 4. Experimental factors that influence the outcome of the Kolbe electrolysis are the current density, the temperature, the pH, additives, the solvent, and the electrode material. 

If carboxylates are subjected to Kolbe electrolysis in the presence of olefins, the generated Kolbe radicals add to the double bonds to afford mainly additive dimers (Table 8, entries 10-17). 

If carboxylates are subjected to Kolbe electrolysis in the presence of olefins, the generated radicals add to the double bonds to afford mainly additive dimers (Table 8, entries 12-20). In vicinal disubstituted styrenes, upon addition of the Kolbe radical Me02CCH2, the yields of adducts decrease with increasing size of the /f-substituent H = 42%, Me = 27%, Et = 11%, /Pr = 5%, tBu = 2% [125]. The ratio of additive dimer 87 (Eq. 11) to monomer 89 can be changed to some extent by the current density i. Upon electrolysis of trifluoroacetate in MeCN-H20-(Pt) in an undivided cell in the presence of electron-deficient olefins, additive dimers and additive monomers are obtained. The selectivity can be controlled by current density, temperature and the substitution pattern of the olefin [126]. Trifluoromethylation of various aromatic compounds with -M substituents has been achieved in satisfactory yield via electrolysis of pyridinium trifluoroacetate in acetonitrile [127]. 

The first successful experiments in the electrolysis of aliphatic carboxylic acids were made by Kolbe.1 These experiments are supplemented by the researches of Kekule,2 Brown and Walker,3 Mulliken,4 and Weems,5 who amplified our knowledge regarding this subject which, still further investigated in the most varied directions by a number of investigators, has yielded valuable results. 

TV-Bromosuccinimide is recommended as a mild, efficient reagent for the a-bromination of acids this reaction, previously considered to be a free-radical process, has now been shown to be ionic in nature, and also to be subject to acid catalysis. A general synthesis of per-acids is provided by per-hydrolysis of acyldiethylphosphates under acid catalysis (Scheme 9) the intermediate esters are prepared by acylation of silver diethyl phosphate (24). This method is useful for the preparation of methoxyaromatic and sterically hindered per-acids, e.g. trimethylperacetic acid teing obtained from pivalic acid in 84% yield. A complementary method involving the intermediacy of acid imid olides has been published. The electrolysis of some a-ketoacids has been studied Kolbe processes can be suppressed under certain conditions. ... 

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