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(also propene), an unsaturated hydrocarbon with the structure CH3—CH=CH2. Propylene is a colorless, combustible gas with a slight odor, a melting point of –185°C, and a boiling point of –47.7°C. Large-scale commercial production of propylene is carried out by the pyrolysis of petroleum fractions and the catalytic dehydrogenation of propane. Propylene is one of the most important building blocks in the petrochemical industry. It is used in the preparation of glycerol (Figure 1,1), acrolein (II), acrylonitrile (III), allyl alcohol (IV), isopropyl alcohol (V), acetone (VI), and phenol (VII).
The interaction of propylene with formaldehyde yields butadiene (VIII); condensation with isobutane yields 2,2,3-tri-methylbutane, or triptane (IX). Polypropylene (X) is obtained by the polymerization of propylene. Propylene-based synthesis products are widely used in the manufacture of such items as plastics, rubbers, detergents, motor fuel components, and solvents.