Abstract: A process for preparing substituted or unsubstituted trifluoroethoxy- or trifluoroethylthiobenzenes by reaction of a phenol or thiophenol, both of which may be substituted or unsubstituted, with a compound of the formula CF.sub.3 --CH.sub.2 --O--R', where R' is a moiety selected from the group consisting of trifluoroacetyl, methanesulfonyl, paratoluenesulfonyl, trichloromethanesulfonyl and chlorosulfonyl, in the presence of a strong alkaline base and a complexing agent of the formula:N--CHR.sub.1 --CHR.sub.2 --O--(CHR.sub.3 --CHR.sub.4 --O).sub.n --R.sub.5 ].sub.3 (II)wherein n is an integer from 0 to 10 (0 is less than or equal to n is less than or equal to 10), R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which may be identical or different, are selected from the group consisting of a hydrogen atom and an alkyl moiety having from 1 to 4 carbon atoms, and R.sub.5 denotes an alkyl or cycloalkyl moiety having from 1 to 12 carbon atoms, a phenyl moiety or a moiety of the formula: --C.sub.m H.sub.2m --C.sub.6 H.sub.