New Method for Selective Monofluorination of Aromatics Using Silver Difluoride

Article abstract of DOI:10.1021/jo01306a011

Fluorobenzene is obtained in 61percent yield from reaction of a solution of benzene in n-hexane with solid argentic fluoride (AgF2).The AgF2 acts as both a strong oxidant and the fluoride source.Cobaltic fluoride provides only low (<8percent) yields of fluorobenzene under similar conditions.The predominant reaction of benzene solutions with AgF2 appears to proceed by a process involving initial electrophilic oxidative cis addition of two fluorine atoms from the solid AgF2 lattice to the para aromatic positions, leading to cis-3,6-difluoro-1,4-cyclohexadiene (F2CHD).The reductive elimination leaves solid argentous fluoride (AgF) which is easily recoverable by filtration.Elimination of HF from the F2CHD yields fluorobenzene.Reactions of haloaromatics with AgF2 generally proceed in a similar manner.Thus, further reaction of AgF2 with benzene or monohalo- or p-dihalobenzenes leads in steps to 3,3,6,6-tetrafluoro-1,4-cyclohexadiene (F4CHD) in up to 82percent yield.The modest to high yields of mono- and specific polyfluorinated aromatics contrast sharply with reported nonselective perfluorination in vapor-phase reactions of aromatics over AgF2 or CoF3.Reactions of AgF2 or CoF3 with solutions of nitrobenzene, acetophenone, benzoic acid, and benzonitrile give mixtures of o-, m-, and p-monofluoro derivatives.