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How does chlorine react with saturated hydrocarbons?

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A labeled diagram of the chlorine element from the periodic table shows its atomic number 17, symbol Cl, electron configuration, and atomic weight range. The box is shaded green to indicate chlorine is a halogen, with icons for orthorhombic crystal structure, gas state at room temperature, and strong acidity. A key explains the icons and colors used. — chlorine Properties of chlorine.

Chlorine reacts with saturated hydrocarbons, such as alkanes, through a process known as free-radical halogenation. This transformation is a type of substitution reaction where a hydrogen atom in the hydrocarbon is replaced by a chlorine atom.12

The reaction is typically initiated by light or heat, which triggers a chain reaction involving the following stages:3

Chain-initiation: Ultraviolet radiation causes a chlorine molecule ( $C l_{2}$ ) to dissociate into two highly reactive chlorine atoms (radicals).3
Chain-propagation: A chlorine radical collides with an alkane molecule, abstracting a hydrogen atom to form hydrogen chloride ( $H C l$ ) and an alkyl radical. This alkyl radical then reacts with another chlorine molecule to produce the final chlorinated product and regenerate a chlorine radical, which continues the cycle.3
Chain-termination: The process concludes when radicals combine, such as two alkyl radicals forming a larger hydrocarbon or a methyl radical combining with a chlorine radical to form an alkyl chloride.3

This method is a primary industrial process for synthesizing various organohalogen compounds.1