Oxychlorination

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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[edit]

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[edit]

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.[3]

References[edit]

  1. ^ M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
  2. ^ Marshall, K. A. 2003. Chlorocarbons and Chlorohydrocarbons, Survey. Kirk-Othmer Encyclopedia of Chemical Technology
  3. ^ "Oxy | Oxychlorination." Oxy | Oxychlorination. N.p., n.d. Web. 10 Oct. 2012. [1]