Electrolytic partial fluorination of organic compounds - XL. Solvent effects on anodic fluorination of heterocyclic sulfides

Solvent effects on electrolytic partial fluorination of alpha-(2-benzoxazol ylthio)-. alpha-(2-benzothiazolylthio)-, and alpha-(2-pyrimidylthio)acetate s were investigated systematically using acetontrile (MeCN) and 1,2-dimetho xyethane (DME) containing Et4NF . nHF (n = 3, 4) as a supporting electrolyt e and a fluoride ion source. MeCN was not suitable for the fluorination of these heterocyclic sulfides since formation of nonconductive polymers on th e anode took place to result in low yields or no fluorination of fluorinate d products. In contrast, the use of DME did nor cause such polymer film for mation and provided much better or excellent fluorinated product yields. Th e superiority of DME can be explained in terms of its ability to solvate th e cationic part of the fluoride salt in which a reactive fluoride ion is le ft for easy attack on the anodically generated cationic intermediate. It is noted that addition of DME into MeCN electrolytic solution markedly increa sed the product yield and current efficiency since the polymer film formati on on the anode and overoxidation of the fluorinated products were effectiv ely suppressed. (C) 2000 The Electrochemical Society. S0013-4651(99)09-017- 5. All rights reserved.