1. A process for isomerizing Z-1,1,1,4,4,4-hexafluoro-2-butene to E-1,1,1,4,4,4-hexafluoro-2-butene comprising:(a) providing a starting material comprising Z-1,1,1,4,4,4-hexafluoro-2-butene;
(b) contacting the starting material with a suitable catalyst in a reaction zone to produce E-HFO-1336mzz; and optionally,
(c) recovering the E-HFO-1336mzz,
wherein, when the contacting step is performed in the gas phase, the catalyst comprises chromium and less than 40% by weight alumina;
wherein when the contacting step is performed in the liquid phase, the catalyst comprises a metal halide wherein the metal halide is aluminum halide, antimony halide, tin halide, tantalum halide, titanium halide, niobium halide, molybdenum halide, iron halide, fluorinated chrome halide, or combinations thereof.