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. This process is attractive industrially because hydrogen chloride is less expensive than chlorine.
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
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
- 2 HCl + CH2=CH2 + ½ O2 → ClCH2CH2Cl + H2O
The HCl from this cracking process is recycled by oxychlorination. The fact that the reaction is self-supplied is one of the reasons that industry uses oxychlorination instead of direct chlorination.
- M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
- Marshall, K. A. 2003. Chlorocarbons and Chlorohydrocarbons, Survey. Kirk-Othmer Encyclopedia of Chemical Technology
- "Oxy | Oxychlorination." Oxy | Oxychlorination. N.p., n.d. Web. 10 Oct. 2012.