Method of preparing highly fluorinated carboxylic acids and their salts

A method for preparing highly fluorinated carboxylic acids and theirs salts and the precursors thereof comprising

• subjecting a highly fluorinated olefin of the general formula (I):
• Rf—(O)n—(CF2)m—CF═CF2 (I)
• to a derivative of formic acid according to the general formula (II):
• HCOR (II)
• in the presence of a radical initiator and activating the initiator to form carboxylic acid precursor in the form of an O-ester, S-ester or an amide adduct of the general formula (III):
• Rf—On—(CF2)m—CFH—CF2—COR (III),
• and optionally, in case the acid is to be obtained, hydrolysing the adduct of formula (III) to form the carboxylic acid or its salt of the general formula (IV):
• Rf—On—(CF2)m—CFH—CF2—COO−M+ (IV),
• wherein in formulae (II) and (III) R represents a residue O−M+, S−M+, OR′, SR′ or NR′R″ wherein R′ and R″ are independent of each other linear or branched or cyclic aliphatic or aromatic residues that contain at least one carbon atom and that do not have an alpha-H-atom and wherein in formulae (I), (III) and (IV) Rf represents H or a perfluorinated or partially fluorinated, linear, branched, aliphatic or aromatic, carbon atoms containing residue and n is either 1 or 0 and m represents an integer between 0 and 6 and M+ represents a cation including H+.