Gas-phase oxychlorination of benzene

Article abstract of DOI:10.1002/recl.19931120405

Homogeneous gas-phase oxychlorination of benzene has been examined in a flow system between 722 and 1174 K.Experiments were performed at atmospheric pressure with nitrogen as an inert carrier gas, containing about equal molar amounts of oxygen, HCl and benzene.Apart from chlorobenzene, substantial amounts of o- and p-chlorophenol are produced.Using benzonitrile rather than benzene, the three isomers of ClC6H4CN are formed in about equal amounts.These findings suggest as homolytic mechanism with aryl radicals as key indermediates.Thermokinetic analysis points to formation of chloro phenols via reaction of phenoxyl (formed from phenyl and oxygen) with HOCl.Chlorination, C6H6 -> C6H5Cl, is explained by reaction between phenyl radicals and HOCl.With increasing temperature (and therefore, oxygen consumption), slow combustion is replaced by pyrolysis as the major reaction channel.As a result, above ca. 1000 K, the production of chlorobenzene diminishes, ultimately being governed by the equilibrium: C6H6 + HCl <*> C6H5Cl + H2.