perfluorobutylsulfonylfluoride CAS No. : 375-72-4 Formula: n-C4F9SO2F Molecular Weight: 302.1 Appearance: colorless or slightly yellow liquid Proportion ( d20D) : 1.700-1.750 Refractive index ( n25D) : 1.2810 Boiling point: 65-66 pH: 3.8-4.8 Content: e 98% Application: It is the homologue of perfluorooctylsulfonylfluoride and can be used to synthetize various of special perfluoro surfactants. Its potassium salt is an excellent anion surfactant and fire retardant for polycarbonate.