PURPOSE: To economically obtain the subject substance useful as a synthetic intermediate for surfactants, agricultural chemicals, medicaments, etc., X-ray contrast media, fluorocarbon-based fire extinguishers, etc., in high yield by thermally reacting a perfluorocarboxylic acid fluoride with LiBr.
CONSTITUTION: A compound expressed by formula I (Rf is perfluorohydrocarbon group; (n) is 1-3) is reacted with LiBr at ≥300°C (preferably 320 to 400°C) to afford a compound expressed by formula II ((m) is 1-3 and (n)≥(m)). The LiBr is preferably anhydrous and the amount thereof used is selected from the range of 1.2 to 1.5mol if the compound expressed by formula I is a monobasic acid, 2.5 to 3.0mol in the case of a dibasic acid and 3.5 to 4.0mol in the case of a tribasic acid. In the case of the dibasic and tribasic acids, only a part of the fluorocarbonyl groups can be substituted with Br by selecting the molar ratio to the LiBr. The compounds expressed by formula I are readily available and the above-mentioned method is advantageous.
HAYASHI EIJI
FUKAYA HARUHIKO
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