Sodium trifluoroacetate, in the presence of copper(t) iodide, is used as a source of trifluoromethyl to replace halogen by trifluoromethyl in benzenoid and heterocyclic aromatic systems, as well as in alkenyl and alkyl halogen compounds. The mechanism of this interesting copper-assisted process has been explored and an intermediate of the form [CF,Cul]-is proposed. Introduction of higher perfluoroalkyl groups from their respective sodium perfluoroalkane carboxylates has been demonstrated and the mechanistic features are compared with those of the trifluoromethylation process.Methods for the introduction of a perfluoroalkyl group into aromatic systems have become especially significant because of the increasing importance of various plant protection products containing trifluoromethyl. Approaches which are now classical include Swarts reactions (CCl, -CF,),' modification of the carboxylate group using sulphur tetrafluoride,' and the use of trifluoroiodomethane as a source of trifluoromethyl viiz a radical (CF,')3 or the use of fluoroiodoalkanes or other halogeno fluoroalkanes as sources of organocopper interm e d i a t e ~. ~ Russian workers have also introduced CF, via (CF,),Hg.' All of these processes have their limitations.Recently Japanese workers briefly described an attractive approach to the introduction of trifluoromethyl which involves the decarboxylation of sodium trifluoroacetate in a copperassisted process. This method has the obvious advantage of a readily accessible and easily handled starting material. We have further investigated the application of this route and attempted to obtain some mechanistic understanding of the process, which is especially interesting since mechanisms of copper-assisted reactions are notoriously difficult to determine.

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Abstract. CoCI2(NCsH4.CH3)2, monoclinic, P2x/n, a= 5.70 (1), b=10.16 (1), c=24.36 (2) A,, fl=92.4 (1) °, Z=4, De= 1.49 g cm -3. C1-Co-CI= 121, N-Co-N= 107°; Co is tetrahedrally coordinated. The molecular packing differs from that of the ZnCI2 and ZnBr2 analogues.

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