Oxychlorination

In organic chemistry, oxychlorination is a process for making C-Cl bonds. In contrast with direct use of Cl₂, oxychlorination uses hydrogen chloride in combination with 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[]

The most common substrate for this reaction is ethylene:

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]

References[]