isobutylene, the unsaturated hydrocarbon (CH₃)₂C=CH₂, a colorless gas. Boiling point, — 6.9°C; density, 0.6266 g/cm³ (at -6.6°C); 1.3814. Isobutene is made industrially by dehydrogenating isobutane over oxide catalysts (forexample, Cr₂0₃ on A1₂0₃) at 500°-600°C or by dehydrating isobutyl alcohol. The ability of isobutene to polymerize and copolymerize is used in industry in making polyisobutene and butyl rubber. Isobutene is also used to alkylate aromatic compounds and isobutane in making isooctane.