Selective activation of methane under mild conditions to produce functionalized products is highly lucrative but remains challenging. The photochemical reaction of anhydrous ferric chloride (FeCl₃) with methane at ambient temperature is an efficient process to selectively chlorinate methane to methyl chloride. An exclusive formation of methyl chloride instead of other multi-chlorinated products is observed, and a maximum initial productivity of 43 g_MeCl?(kg_Fe?h)^–1 was obtained under irradiation with a 300-watt high-pressure mercury lamp or solar light. Ferric chloride functions both as the source of reactive chlorine radicals and as the oxidant, and it was concomitantly reduced to ferrous chloride. The reaction rate increases with the power of the lamp and the concentration of ferric chloride. Interestingly, the reaction temperature from 25 to 75 ℃ and the methane pressure in the range of 1~4 MPa had little influence on the reaction rate. Methyl chloride was hydrolyzed to methanol with elimination of hydrogen chloride, and the ferrous product was re-oxidized to the ferric analog by oxygen in the air in the presence of hydrogen chloride, thus completing the loop of both iron and chlorine.

Key words: C—H activation, methane activation and functionalization, metal-catalyzed synthetic reaction, photocatalysis