A model for the gas phase oxidation of hydrogen chloride in the presence of copper (II) chloride (the Deacon reaction) has been investigated by the density functional theory. Chlorine (Cl-2) is produced by the thermal decomposition of CuCl2 generating Cu2Cl2 which reacts with O-2 ((3)Sigma(g)) to form several intermediates and complexes which further react with hydrogen chloride. A key step in the mechanism is the fission of a O-O linkage between two Cu2Cl2 moieties. This step possesses a barrier prohibitive to homogeneous gas phase catalysis but one which is expected to be easily overcome on a copper chloride surface. (C) 2010 Elsevier B.V. All rights reserved.