Nucleophilic addition of hydrogen fluoride

This nucleophilic addition of hydrogen fluoride can be effected by ammonium fluoride, potassium fluoride, or tetraethyl- or tetrabutylammonium fluoridc in formamide or chloroform.For example, formation of 1,1,1,2,3,3,3-heptafluoropropane. ... 

Table 8 summarizes further examples of the nucleophilic addition of hydrogen fluoride to pcrhalogenated alkenes with potassium fluoride in formamide. 

The greater stability of the digonal vinyl cation 161 than of the bridged cation 162 would imply that, at least in the gas phase, race-mization is involved as stereochemical course of any reaction with nucleophiles since both lobes of the empty p-orbital of 161 are available for a nucleophilic attack. Efforts to rationalize (Bumelle, 1964) early reports of stereospecific trans addition to acetylene derivatives have recently been complemented by a theoretical calculation of the energy profile for addition of hydrogen fluoride to acetylene in the gas phase (Hopkinson et at., 1971). The results of these calculations suggest that the bridged cation is possibly a transition state and not an intermediate. 

Benzodiazepines have been prepared from perfluoroenones, prepared in situ, for example Scheme 12 (94TL4357).This reaction obviously closely resembles the preparative method starting from ynones but, in addition to nucleophilic addition and condensation reactions, elimination of hydrogen fluoride is also involved. 

For this reason, electrophilic additions such as addition of hydrogen halides are very difficult, as can be seen in Explanations 13, 14, and 15. But because of the low overall electron density, the double bonds in perfluoroalkenes are easily attacked by nucleophiles such as fluoride ion. If perfluoropropene is treated with dry potassium fluoride in a proton-donor solvent such as formamide, the fluoride anion joins the less negative carbon of the double bond and forms a negatively charged intermediate that readily reacts with the proton of formamide to give 2 H-perfluo-ropropane [5/]. Such a nucleophilic addition takes place with other fluorides such as cesium fluoride, tetraethylammonium fluoride, and sil-... 

The reaction starts probably with dehydrofluorination to give an oc, 3-unsaturated ketone. This undergoes a nucleophilic addition of water, and a loss of hydrogen fluoride from the intermediate affords a (3-diketone. 

The electron-deficient double bond in lH-pentafluoropropene reacts easily with nucleophiles such as azide anion to form primarily an addition product l-azido-l,2,3,3,3-pentafluoropropane. In the basic medium, unsaturated l-azido-2,3,3,3-tetrafluoropropene is also formed, either by elimination of hydrogen fluoride from the addition product, or by direct displacement of fluorine by SN2 mechanism [90]. 

The proton-proton HNCH spin-spin coupling in A-methylaniline is affected by the p fa value of the proton acceptor partner. PhsPO, PhsAsO and F ions are used in order to elucidate this dependence. The importance of the hydrogen bonding interaction is observed also in aniline reactions. In fact, the addition of potassium fluoride to the reaction mixtures of anilines and alkyl halides strongly enhances the A-alkylation reaction because the nucleophilicity of aromatic amines is increased by hydrogen bond interaction with fluoride ion151. 

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