In chemistry, oxychlorination is a process for generating the equivalent of chlorine gas (Cl₂) from hydrogen chloride and oxygen.^[1] This process is attractive industrially because hydrogen chloride is less expensive than chlorine.^[2]

Mechanism

The reaction is usually initiated by copper(II) chloride (CuCl₂), which is the most common catalyst in the production of 1,2-dichloroethane. In some cases, CuCl₂ is supported on silica in presence of KCl, LaCl₃, or AlCl₃ as cocatalysts. Aside from silica, a variety of supports have also been used including various types of alumina, diatomaceous earth, or pumice. Because this reaction is highly exothermic (238 kJ/mol), the temperature is monitored, to guard against thermal degradation of the catalyst. The reaction is as follows:

CH₂=CH₂ + 2 CuCl₂ → 2 CuCl + ClH₂C-CH₂Cl

The copper(II) chloride is regenerated by sequential reactions of the cuprous chloride with oxygen and then hydrogen chloride:

½ O₂ + 2 CuCl → CuOCuCl₂

2 HCl + CuOCuCl₂ → 2 CuCl₂ + H₂O

Applications

Oxychlorination is employed in the conversion of ethylene into vinyl chloride. In the first step in this process, ethylene undergoes oxychlorination to give ethylene chloride:

CH₂=CH₂ + 2 HCl + ½ O₂ → ClCH₂CH₂Cl + H₂O

Oxychlorination is of special importance in the making of 1,2-dichloroethane, which is then converted into vinyl chloride. As can be seen in the following reaction, 1,2-dichloroethane is cracked:

ClCH₂CH₂Cl → CH₂=CHCl + HCl

The HCl from this cracking process is recycled by oxychlorination in order to reduce the consumption of raw material HCl (or Cl₂, if direct chlorination of ethylene is chosen as main way to produce 1,2-dichloroethane).^[3]

Iron(III) chloride is produced commercially by oxychlorination (and other methods). For example, dissolution of iron ores in hydrochloric acid gives a mixture of ferrous and ferric chlorides:^[4]

Fe₃O₄ + 8 HCl → FeCl₂ + 2 FeCl₃ + 4 H₂O

The iron(II) chloride is converted to the iron(III) derivative by treatment with oxygen and hydrochloric acid:

4 FeCl₂ + O₂ + 4 HCl → 4 FeCl₃ + 2 H₂O