Solvent effects on electrolytic partial fluorination of alpha-(2-benzoxazolylthio)-. alpha-(2-benzothiazolylthio)-, and alpha-(2-pyrimidylthio)acetates were investigated systematically using acetontrile (MeCN) and 1,2-dimethoxyethane (DME) containing Et4NF . nHF (n = 3, 4) as a supporting electrolyte and a fluoride ion source. MeCN was not suitable for the fluorination of these heterocyclic sulfides since formation of nonconductive polymers on the anode took place to result in low yields or no fluorination of fluorinated products. In contrast, the use of DME did nor cause such polymer film formation and provided much better or excellent fluorinated product yields. The superiority of DME can be explained in terms of its ability to solvate the cationic part of the fluoride salt in which a reactive fluoride ion is left for easy attack on the anodically generated cationic intermediate. It is noted that addition of DME into MeCN electrolytic solution markedly increased the product yield and current efficiency since the polymer film formation on the anode and overoxidation of the fluorinated products were effectively suppressed.