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How does chlorine react with unsaturated 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.

When chlorine reacts with unsaturated hydrocarbons, it readily undergoes an addition reaction, where chlorine atoms add directly to the carbon-to-carbon double or triple bonds.1

This process effectively breaks the multiple bond, allowing the carbon atoms to become saturated with the additional chlorine atoms. A classic example is the addition of chlorine to ethylene, which produces dichloroethane, a key intermediate in the industrial production of vinyl chloride.234

While chlorine can also participate in substitution reactions with organic compounds—where it replaces hydrogen atoms—its interaction with unsaturated hydrocarbons is characterized by this rapid addition to the multiple bonds. These reactions are often initiated by electrophilic reagents, where the electron-rich nature of the double or triple bond facilitates the attack.125