Hypofluorous acid-acetonitrile complex

Abstract

[147583-45-7] C2H4FNO (MW 77.07) InChI = 1S/C2H3N.FHO/c1-2-3;1-2/h1H3;2H InChIKey = MHXSJBXDLWNIAN-UHFFFAOYSA-N (the HOF·CH3CN complex is used for tertiary hydroxylations,2 epoxidations,3 oxidation of amines,4 alcohols and ketones,5 aromatics,6 sulfides and thiophenes,7 amino acids,8, ethers,9 and acetylenes.10 It is also useful in other oxygen transfer reactions such as hydroxylations α to carbonyls11 and the preparation of tertiary N-oxides12) Physical Data: (for the non-complexed HOF): mp −117 °C; bp −79 °C (1 Torr); 19F NMR +27.5 ppm. 19F NMR for the HOF· MeCN complex: −8.5 ppm. Enthalpy of formation of the complex: 14.3 kJ mol−1.13 Handling, Storage, and Precautions: while HOF is a very unstable substance and of little use in synthetic chemistry, its acetonitrile complex is much more stable. Nevertheless, it has to be prepared in situ and for all practical purposes reacted soon after its formation. The concentration of the reagent is determined iodometrically (HOF+2KII2+KF+KOH). The reagent may be toxic and should be treated accordingly. Still, since it is an heavy metal-free agent, and its only side product is aqueous HF which may be easily neutralized, it is considered to be an ecologically friendly reagent.5a Free HOF was originally synthesized by Appelman,14 but it was hardly a useful synthetic reagent since it was difficult to make, could be generated only in very minute amounts and has a very short half-life time at temperatures above −100 °C. Even so, it was demonstrated that it can react with a few unsaturated compounds.15 Some years ago it was discovered that a much more stable form of HOF can be prepared simply by passing commercially available prediluted F2 through aqueous acetonitrile thus forming a stabilized complex HOF·MeCN.1 It should be noted that it is also possible to prepare any desirable F2/N2 mixtures from 95% fluorine and nitrogen using a vacuum line system.12 The X-ray structure of the complex16 reveals that the acetonitrile nitrogen atom is coordinatively bonded to the hydrogen atom of the HOF forming almost a straight chain with the of bond forming an angle of 93° (eq 1). The reagent possesses a strongly electrophilic hydroxylium moiety (HO+) turning the reagent into an excellent oxygen transfer agent. (1)