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1. Fluorination with anhydrous hydrogen fluoride and its complexes with bases of different class compounds

Hydrofluorination with anhydrous hydrogen fluoride can be carried

1.in gas phase over catalysts
2.in liquid phase in the presence of antimony halides
3. as a liquid-phase non-catalytic process
4. hydrofluorination with hydrogen fluoride/base complexes is used to be carried in liquid phase using polar solvents.

Hydrofluorination in gas and liquid phase in the presence of catalysts is widely used in production of various chladones. The experimental date file on these processes is very huge and this review considers only new data on synthesis of ozone safety chladones without chlorine and bromine atoms. In these cases halogenated olefins and alkanes are used as initial substrates.

Anhydrous hydrogen fluoride is a relative strong acid which is inert towards oxidizers and reducing agents while it is a good dissolvent for many organic compounds. A low boiling point of hydrogen fluoride allows to isolate it after reaction and then to introduce it again into the process. These properties of hydrogen fluoride are widely used in organic synthesis for reaction medium combining properties of acid reagent and solvent. 

Stability towards reducing processes makes hydrogen fluoride a perfect medium for processes of hydrogenation [19,20]. Besides anhydrous hydrogen fluoride possesses a catalytic effect in hydrogenation of different aromatic compounds, aliphatic ketones, esters of carbonic acids and anhydrides in the presence of platinum dioxide [20].

A classical example of hydrogenation of nitro-aromatic compounds in a medium of anhydrous hydrogen fluoride runs under mild conditions to form appropriate anilines. It should be noted that sometimes introduction of fluorine into benzene ring takes place and the reasons of that will be discussed below [21,22].

Fluorination of the C-H bonds in the hydrocarbon chain under influence of hydrogen fluoride takes place only in the presence of oxidizers and is realized only for benzene derivatives. A number of such processes is realized in a medium of hydrogen fluoride. Thus, there has been realized oxidizing fluorination of the C-H bond for toluene [23] and ethyl benzene derivatives [24] by hydrogen fluoride in the presence of lead oxide [23], NiO₂ [23], AgF₂ [24], CoF₃ [24], Co(OAc)₃ [24].

But HF-PbO₂ system in case of absence of alkyl groups can fluorinate the benzene ring to give a cyclohexadiene structure [25]. So, interaction of phenol with 70% HF/Py or KF/HF system in the presence of PbO₂ results in formation of 4,4-difluorocyclohexa-2,5-dienone [25].

In case of unsaturated organic compounds the reaction with anhydrous hydrogen fluoride in the presence of PbO₂ or Pb(OAc)₄ results in the fluorine adduct to the double bond without replacement hydrogen or chlorine atoms [26].

Steroids are fluorinated by this system regioselectively to form cis-difluorosteroids [27].

Anhydrous hydrogen fluoride is an excellent reagent for intermolecular cyclizations. So, diethylarylmalonate gives tetralone derivatives in good yield [28].

-Benzamidoacetophenone turns into 2,5 diphenyloxazoline [29]

Hydrogen fluoride in acetonitrile is a good catalyst for intermolecular Diels-Alder reactions [30]. This reagent promotes high stereoselectivity of cyclization of triene ethers while the use of different acids, HCl, HAc, CF₃COOH results in polymerization products.

It is important that hydrogen fluoride is convenient to use in industrial technologies because of its relative cheapness and easiness in handling in gas-phase flow continuous systems over catalysts and in liquid-phase processes. But these reactions require apparatus designed for high pressure and high temperature.

It is relatively easy to replace haloids atoms bound with a double bond or benzene ring. Thus, conversion of benzotrichloride to benzotrifluoride, the main semi-product for synthesis of pesticides and medicine preparations, under influence of anhydrous hydrogen fluoride runs within a comparatively wide temperature interval in high yields [31-33].

An analogous reaction has been implemented for chlorinated homologues of pyridine also [34].