The activation of saturated hydrocarbons by transition-metal complexes in solution. Part IV. Oxidation of benzene and of alkanes by hexachloroplatinate(IV)

Abstract

Benzene is oxidised to chiorobenzene by H₂PtCl₆ in aqueous trifluoroacetic acid at 120 °C. The initial formation of a water-soluble complex of platinum(IV) and benzene is accelerated by an increase in the H₂PtCl₆ concentration and by addition of K₂[PtCl₄], and is reduced by the addition of chloride ion. Subsequent reactions give chlorobenzene; some of it complexes with platinum. An analogous study has been made of the oxidation of alkanes, particularly hexane, using the same system. Evidence for the formation of chlorohexanes from hexane and of platinum complexes with hydrocarbon ligands has been obtained. 2- and 3-chlorohexanes are further oxidised and, from determinations of the amount of Pt^IV reduced during the reaction, it appears likely that polychlorinated carboxylic acids are formed. The mechanisms of aromatic and alkane oxidation in this system are initially very similar. The reaction of cyclohexane with H₂PtCl₆ is more complex. In addition to chlorination, dehydrogenation occurs to give benzene and chlorobenzene.