PURPOSE: To site-selectively produce the subject compound under mild condition by reacting a fluoride ion with an aromatic dithiocarboxylic acid ester or a substituted thiodifluoromethyl-substituted aromatic compound in the presence of a halonium ion generator.

CONSTITUTION: The objective compound of formula III such as 1-trifluoro- methylnaphthalene can be produced by reacting (A) a fluoride ion source such as hydrogen fluoride, complex of hydrogen fluoride and an amine or quaternary ammonium dihydrogen trifluoride with (B) a compound of formula I [R1 is (substituted) aryl; R2 is R1 or (substituted) alkyl] (e.g. 1-naphthalenedithiocarboxylic acid methyl ester) or a compound of formula II [e.g. 1-difluoro(methylthio)methylnaphthalene] in the presence of (C) a halonium ion generator such as 1,3-dibromo-5,5-dimethylhydantoin or N-bromosuccinimide preferably at 0-80°C.