Fully Fluorinated Alkoxides: Part I. Trifluoromethoxides of Alkali Metals

Abstract

The preparation is described of the trifluoromethoxides of the heavier alkali metals, i.e. MOCF, where M = K, Rb, or Cs. These are stable, crystalline, ionic solids made by the reversible reaction of carbonyl fluoride with the appropriate metal fluoride. No trifluoromethoxides could be prepared from lithium, sodium, barium, or thallium(1) fluorides. Factors affecting the relative stability of such compounds are discussed.Trifluoromethanol, CFBOH, is not known, and is generally assumed to be incapable of existence because of the ease with which compounds having a fluorine atom in a position a to a hydroxyl group would eliminate hydrogen fluoride. Because of this unavailability of the parent alcohol, no metallic trifluoromethoxides have hitherto been reported. We now report the preparation of stable, crystalline trifluoromethoxides of the heavier alkali metals, i.e. MOCF3, where RII = K, Rb, or Cs.A consideration of the possible formation of metallic trifluoromethoxides shows a t once that they are likely to be more ionic in nature than the corresponding methoxides. The completely ionic formulation M+[OCFJd would contain the trifluoromethoxide ion, isoelectronic with the fluoroborate ion, BF4-. The charge in the trifluoromethoxide ion rests formally on the oxygen atom, but it would be shared to some extent by the three fluorine atoms because of their greater electronegativity. The distribution of charge over the whole ion achieved in this way should therefore stabilize it, in a manner not possible in the ionic non-fluorinated methoxides of the alkali metals. The stability of a solid ionic trifluoromethoxide would clearly be influenced by the nature of the cation present, since smaller cations, or those with a high ratio of charge to size, would cause greater polarization of the anion and a correspondingly greater tendency towards decomposition to give a fluoride ion and carbonyl fluoride. In other words, the equilibrium:would be displaced to the left by the presence of large cations. An immediate corollary of this suggestion is that by approaching the equilibrium from the direction of formation rather than decomposition one would have available a possible synthetic route to trifluoromethoxides.

Pyrolytic Decarboxylation of Some Derivatives of Perfluorinated Mono- and Dicarboxylic Acids

“…The yields of perfluorinated methyl vinyl ether and tetrafluoroethylene were 30 and 60 mol %, respectively. With Na + replaced by K + , the yield of tetrafluoroethylene increases from 60 to 95 mol %, suggesting stabilization of the trifluoromethoxide anion with the potassium ion, in agreement with the data of [5,6]. …”

“…Low-boiling gases were passed through a trap with liquid bromine and then through an alkaline absorber. From the trap, we isolated 4 g (yield~15%) of a product identified as perfluoro-2-methyloxolan-3-one VIII by comparison of the 19 F NMR and mass spectra with those reported in [6]; bp~15oC. In the trap with bromine, 1,2-dibromotetrafluoroethane was obtained as a separate phase.…”

Investigation of fluorinated surfaces by means of radio-labelled probe molecules

“…An important observation made early on was that the kinetic performance of Cs 18 F in the [ 18 F] exchange reactions could be improved significantly if the compound had been activated by prior formation and subsequent thermal decomposition of the alkoxides, Cs + [OC 18 F(CF 3 ) 2 ] À or Cs + [OCF 2 18 F] À1 [14]. These are available readily by reaction between CsF and (CF 3 ) 2 CO or F 2 CO [17]. The treatment introduces an extra stage into the labelling process but is justified by the increased level of [ 18 F] incorporation achievable.…”

A New and Direct Trifluoromethoxylation of Aliphatic Substrates with 2,4‐Dinitro(trifluoromethoxy)benzene

“…Several teams tried to draw this equilibrium towards CF 3 O À and demonstrated that if fluorides are associated with rather bulky cations [CsF, [23,24] (Me 2 N) 3 S + Me 3 SiF 2 À [25] ], the resulting trifluoromethoxide could be stable enough, in solution, to react with reactive electrophiles such as benzyl bromide [24] or primary triflates and bromides. [26] Nevertheless, the development of this reaction was limited by the high toxicity of gaseous fluorophosgene.…”