Facile, Temperature-Dependent Formation of Gaseous C1 and C2 Perfluoroalkyl Hypofluorites. Applications as Electrophilic Fluorinating Agents.

Article abstract of DOI:10.1021/jo00359a018

A convenient method for continuous-flow production of gaseous C1 and C2 fluoroxyperfluoroalkanes (R_fOF) was developed.Passage of 10percent F2 through short columns of CF3CO2Na resulted in the formation of the following hypofluorites: CF3CF2OF, CF3OF, CF3CF(OF)2, and CF2(OF)2.No other significant oxidizing side products or residual F2 were present in the column effluent under normal conditions.Identifications of the hypofluorites were made through direct 19F NMR measurements at -40 deg C of the -196 deg C condensate of the column effluent and also on the basis of stilbene trapping experiments.Hypofluorites were formed rapidly at temperatures at least as low as -110 deg C but no reaction occurred at -160 deg C.The ratios of hypofluorites formed strongly depended on the temperature of the salt column.Yields of CF3CF(OF)2 exceeding 90percent, based on input F2, were obtained at salt temperatures between -110 and -78 deg C.At moderate temperatures (-20 to +20 deg C) CF3CF2OF was the predominant products, accompanied by significant amounts of CF3OF and CF3CF(OF)2 and traces of CF2(OF)2.CF3OF was the major hypofluorite formed at high (60 to 100 deg C) temperatures.No hypofluorites were detected when the column temperature was above 135 deg C.A minimum of specialized equipment is required to produce hypofluorites by this method.It makes expensive or previously exotic, little-studied fluoroxy compounds readily available for synthetic applications.Fluorinations of anisole, 3,4,6-triacetyl-D-glucal, phenylmercuric acetate, and N,N-dimethylphenylacetamide tert-butyldimethylsilyl enolate were carried out to demonstrate the synthetic utility of R_fOF and to compare its chemical reactivity with acetyl hypofluorite, an electrophilic fluorinating agent currently in wide use.R_fOF, used as a homogeneous reagent, was comparable in fluorinating ability but was less regio- and stereoselective than acetyl hypofluorite in the cases examined.