Propylene, also known as propene, is an unsaturated organic compound having the chemical formula C3H6. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons, and it is also second in natural abundance.

At room temperature, propylene is a gas, and as with many other alkenes, it is also colourless with a weak but unpleasant smell.
Propylene has a higher density and boiling point than ethylene due to its greater size. It has a slightly lower boiling point than propane and is thus more volatile. It lacks strongly polar bonds, yet the molecule has a small dipole moment due to its reduced symmetry (its point group is Cs).
Propylene has the same empirical formula as cyclopropane but their atoms are connected in different ways, making these molecules structural isomers.

Propylene is produced from non-renewable fossil fuels - petroleum, natural gas and to a much lesser extent coal. Propylene is a byproduct of oil refining and natural gas processing. Ethylene, propylene, and other compounds are produced by cracking larger hydrocarbon molecules. Propylene is separated by fractional distillation from hydrocarbon mixtures obtained from cracking and other refining processes.

Production and Uses
Propylene is the raw material for a wide variety of products including polypropylene, a versatile polymer used in packaging and other applications. It is the second highest volume petrochemical feedstock after ethylene. Propylene and benzene are converted to acetone and phenol via the cumene process. Propylene is also used to produce isopropanol (propan-2-ol), acrylonitrile, propylene oxide (epoxypropane) and epichlorohydrin.
 Propylene production has remained static at around 35 million tonnes (Europe and North America only) from 20002008 but has been increasing in East Asia, most notably Singapore and China. Total world production of propylene is currently about half that of ethylene.

Propylene resembles other alkenes in that it undergoes addition reactions relatively easily at room temperature. The relative weakness of its double bond (which is less strong than two single bonds) explains its tendency to react with substances that can achieve this transformation. Alkene reactions include: 1) polymerization, 2) oxidation, 3) halogenation and hydrohalogenation, 4) alkylation, 5) hydration, 6) oligomerization, and 7) hydroformylation.

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