Addition reactions of fluoroalkenes

Summary

• 1. Perfluoropropene, in presence of alkalis, readily unites with alcohols and thiols, and the hydrogen atom of the hydroxyl group of the alcohol or of the mercapto group of the thiol, in contrast to its behavior, in the case of propene, adds to the middle carbon atom of perfluoropropene.

• 2. The alkyl 2H-hexafluoropropyl ethers formed as a result of reaction of perfluoropropene with alcohols are readily hydrolyzed into esters of 2H-tetrafluoropropionic acid (proof of direction of addition).

• 3. The normal addition reaction, leading to formation of alkyl 2H-hexafluoropropyl ethers, is accompanied by the formation in appreciable amount of alkyl perfluoroallyl ethers (or alkyl perfluoroallyl sulfides in the case of reaction with thiols).

• 4. It has been established that the fluorine atoms of the trifluoromethyl group of perfluoropropene, unlike those in compounds carrying a trifluoromethyl group on an atom not linked to a neighbor by a multiple bond, have an appreciable degree of mobility.

• 5. The formation of perfluoroallyl derivatives in reactions of perfluoropropene with substances containing mobile hydrogen atoms (alcohols, thiols, etc.) cannot be regarded as a direct replacement of a fluorine atom of the trifluoromethyl group (by alkoxyl or alkylthio), but is the result of anionoid attack by a nucleophilic reagent on the extreme carbon atom of perfluoropropene having the least electron density; in the moment of attack, transposition of the double bond occurs, and one of the fluorine atoms of the trifluoromethyl group is removed as an anion.