In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, ...
, oxychlorination is a process for making C-Cl bonds. In contrast with direct use of Cl
2, oxychlorination uses
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
in combination with
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
.
[{{Ullmann, author=M. Rossberg , display-authors=et al., title=Chlorinated Hydrocarbons, year=2006, doi=10.1002/14356007.a06_233.pub2] This process is attractive industrially because hydrogen chloride is less expensive than chlorine.
Mechanism
The reaction is usually initiated by
copper(II) chloride
Copper(II) chloride is the chemical compound with the chemical formula CuCl2. The anhydrous form is yellowish brown but slowly absorbs moisture to form a blue-green dihydrate.
Both the anhydrous and the dihydrate forms occur naturally as the ver ...
(CuCl
2), which is the most common catalyst in the production of
1,2-dichloroethane
The chemical compound 1,2-dichloroethane, commonly known as ethylene dichloride (EDC), is a chlorinated hydrocarbon. It is a colourless liquid with a chloroform-like odour. The most common use of 1,2-dichloroethane is in the production of vin ...
. In some cases, CuCl
2 is
supported on silica in presence of KCl, LaCl
3, or AlCl
3 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:
:CH
2=CH
2 + 2 CuCl
2 → 2 CuCl + ClH
2C-CH
2Cl
The copper(II) chloride is regenerated by sequential reactions of the cuprous chloride with oxygen and then
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
:
:½ O
2 + 2 CuCl → CuOCuCl
2
:2 HCl + CuOCuCl
2 → 2 CuCl
2 + H
2O
Applications
The most common substrate for this reaction is
ethylene:
:CH
2=CH
2 + 2 HCl + ½ O
2 → ClCH
2CH
2Cl + H
2O
Oxychlorination is of special importance in the making of 1,2-dichloroethane, which is then converted into
vinyl chloride
Vinyl chloride is an organochloride with the formula H2C=CHCl. It is also called vinyl chloride monomer (VCM) or chloroethene. This colorless compound is an important industrial chemical chiefly used to produce the polymer polyvinyl chloride (PVC ...
. As can be seen in the following reaction, 1,2-dichloroethane is cracked:
:ClCH
2CH
2Cl → CH
2=CHCl + HCl
The HCl from this cracking process is recycled by oxychlorination in order to reduce the consumption of raw material HCl (or Cl
2, if direct chlorination of ethylene is chosen as main way to produce 1,2-dichloroethane).
Chemistry of the Oxychlorination Catalyst: An In situ, Time-resolved, Dispersive XANES Study — ESRF - European Synchrotron Radiation Facility
/ref>
References
Organic reactions
Inorganic reactions
Halogens