Synthesis of 1,1,2,2,3,3,4,4-octafluoro-4-[(1,2,2-trifluoroethenyl)oxy]butanesulfonyl fluoride

We investigated two synthetic routes (Route A: first synthesis of the CF₂CFO group and then the SO₂F group, Route B: first synthesis of the SO₂F group and then the CF₂CFO group) to synthesize CF₂CFO(CF₂)₄SO₂F (SSC monomer), the raw material for the short-side-chain perfluorinated polymer electrolyte membrane, from I(CF₂)₄I using the same commercially available reagents but in different order of use. In Route A, by-products [CF₂CFO(CF₂)₄I and the compound presumed to have the structure of CF₂SO₂F] were formed in the second half of the synthesis of SSC monomer, but they were difficult to remove from SSC monomer. On the other hand, in Route B, by-product I(CF₂)₄I formed in the first half of the synthesis of SSC monomer was easily removed by the conversion with oleum. In addition, the reaction of I(CF₂)₄I with Na₂S₂O₄ produced I(CF₂)₄SO₂Na and NaO₂S(CF₂)₄SO₂Na, which were separated by the extraction operation with ethyl acetate, and NaO₂S(CF₂)₄SO₂Na was converted to I(CF₂)₄I by chlorine gas in the presence of NaI. We chose Route B and obtained high-purity SSC monomer.