To provide a process for producing a desired perfluorinated product at a high yield in a fluorination reaction of a partially fluorinated ester.
A perfluorinated compound (4) is obtained by fluorinating in a liquid phase a compound (3) (wherein the fluorine content is at least 30 mass %) obtained by reacting a compound (1) and a compound (2), wherein the compound (1) is HOCH
2
—R
A
—CH
2
OH, the compound (2) is X
1
C(═O)—C(R
B
)(R
C
)(R
D
), R
A
is a bivalent saturated hydrocarbon group or the like which has no hetero atom such as an etheric oxygen atom, X
1
is a halogen atom, and —C(R
B
)(R
C
)(R
D
) is a branched group.
Polyfluorodiacyl fluorides having the formula FOC(CFXOCF.sub.2).sub.p (CF.sub.2).sub.n-1 (CF.sub.2 OCFX).sub.q COF wherein n represents an integer of 2 to 4; X represents fluorine or chlorine atom or trifluoromethyl group; p=0 to 5; q=0 to 5; p+q>1 are produced by reacting a perfluorolactone with a fluorocarbon epoxide, optionally in the presence of an aprotic polar solvent and a nucleophilic reagent.