The successful synthesis of CF3OH by HF addition across the C=O double bond of carbonyl fluoride [1] prompted us to study the reaction chemistry of cyano-compounds and nitriles with anhydrous HF. While the [CF3NH3]+ cation has previously been prepared by relatively cumbersome multi-step syntheses [2], we obtained the trifluoromethyl ammonium cation in a one-step reaction at room temperature from commercially available starting materials. Simple Br/F or Cl/F exchange and HF addition across the C≡N triple bond of BrCN or ClCN, respectively, in anhydrous HF solution produces the desired trifluormethyl ammonium cation in quantitative yield. The resulting [CF3NH3]+[HF2-] was converted into stable [AsF6]- and [SbF6]- salts by addition of AsF5 or SbF5, respectively. Other fluoroalkylammonium ions, such as [HCF2NH3]+, [CF3CF2NH3]+, [HCF2CF2NH3]+ or [(CF2NH3)2]2+ were obtained from the corresponding nitrile compounds. When the cyano-compounds and nitriles were reacted with HF/MF5 rather than pure HF, only protonation under formation of the corresponding nitrilium ion [RHCNH]+ (R = H, Me, Et, n-Pr, C6H5, Cl, Br) was observed. Multinuclear NMR and vibrational spectroscopy, crystal structures and theoretical calculations were used to characterize the compounds. [1] K. O. Christe, J. Hegge, B. Hoge, R. Haiges, Angew. Chem. Int. Ed. 46, 2007, 6155. [2] G. Klöter, W. Lutz, K. Seppelt, W. Sundermeyer, Angew. Chem. Int. Ed. 16, 1977, 707; G. Klöter, K. Seppelt, J. Am. Chem. Soc. 101, 1979, 347.

Reactions of nitriles with anhydrous HF: Synthesis of nitrilium and a-fluorinated alkylammonium salts

251st National Meeting (2016)

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