Purification of perfluorosulfonyl fluoride perfluorovinyl ethers by thermal decomposition of unstable isomers

Process of claim [1] 3 wherein the primary isomer is perfluoro-3,6-dioxa-4-methyl-7-octene-sulfonyl fluoride and there is also present in the mixture the isomer perfluoro-3,6-dioxa-5-methyl-7-octene-sulfonyl fluoride.

In the process for the preparation of perfluorosulfonyl fluoride perfluorovinyl ethers having the formula ROCF=CF.sub.2, where R is a sulfonyl fluoride containing fluorocarbon group of three to 15 carbon atoms which may optionally contain one or more ether linkages or chlorogroups with the proviso that the carbon atom of R bonded to the oxygen is also bonded only to atoms from the class consisting of carbon and fluorine, wherein mixtures of the primary isomer and other isomer thereof having the same number of fluorine and oxygen atoms per molecule as the primary isomer are present, the improvement comprising an additional heating of said mixture consisting essentially of said isomers at a temperature of between 250.degree.-350.degree. to selectively destroy said other isomer and separating the purified primary isomer from the products of the destroyed isomer, the --OCF=CH.sub.2 group of the primary isomer being connected to a CF.sub.2 group in R and the --OCF=CF.sub.2 group of said other isomer being connected to a secondary or tertiary carbon atom.