There is provided a method for producing high-purity bromine pentafluoride while leaving a less amount of an unreacted fluorine gas. The method for producing bromine pentafluoride includes a reaction step of feeding a bromine-containing compound, which is at least one of a bromine gas and bromine trifluoride, and a fluorine gas to a reactor to give a (fluorine atom):(bromine atom) molar ratio, that is, F/Br of 3.0 or more and 4.7 or less and reacting the bromine-containing compound and the fluorine gas to each other to obtain a reaction mixture containing bromine pentafluoride and bromine trifluoride; and a separation step of separating bromine pentafluoride and bromine trifluoride in the reaction mixture from each other.

Production of C.sub.16 to C.sub.30 saturated hydrocarbon by alkylating a reactant aromatic hydrocarbon with a C.sub.6 to C.sub.24 olefin to produce alkylation product comprising a C.sub.16 to C.sub.30 alkyl aromatic hydrocarbon and subsequent hydrogenation of the alkylation product to produce hydrogenated product comprising a C.sub.16 to C.sub.30 saturated hydrocarbon. The C.sub.16 to C.sub.30 alkyl aromatic hydrocarbon comprises an aromatic C.sub.6 ring and one or more C.sub.6 to C.sub.24 alkyl groups attached thereto. The C.sub.16 to C.sub.30 saturated hydrocarbon comprises a saturated C.sub.6 ring and one or more C.sub.6 to C.sub.24 alkyl groups attached thereto.

Production of C.sub.16 to C.sub.30 saturated hydrocarbon by alkylating a reactant aromatic hydrocarbon with a C.sub.6 to C.sub.24 olefin to produce alkylation product comprising a C.sub.16 to C.sub.30 alkyl aromatic hydrocarbon and subsequent hydrogenation of the alkylation product to produce hydrogenated product comprising a C.sub.16 to C.sub.30 saturated hydrocarbon. The C.sub.16 to C.sub.30 alkyl aromatic hydrocarbon comprises an aromatic C.sub.6 ring and one or more C.sub.6 to C.sub.24 alkyl groups attached thereto. The C.sub.16 to C.sub.30 saturated hydrocarbon comprises a saturated C.sub.6 ring and one or more C.sub.6 to C.sub.24 alkyl groups attached thereto.