The anodic oxidation of alkanes in anhydrous hydrogen fluoride and related superacid media

The anodic oxidation of several alkanes in anhydrous hydrogen fluoride at various acidity levels, from “basic” media (KF) to “acid” media (SbF₅) has been studied to establish optimum conditions for the formation of carbenium ions. The oxidation potential of an alkane depends on structure and on the acidity level of the medium. Taking into account thermodynamical data, possible mechanisms for the anodic oxidation are proposed. Furthermore, it is shown that alkanes undergo spontaneous chemical oxidation in acid media (HF + SbF₅ which may be investigated in its kinetic and thermodynamic aspect by means of electroanalytical methods.     

Electrochemical oxidation of pentafluorophenol in hydrogen fluoride and superacid media

The electrochemical behaviour of pentafluorophenol was examined by means of Classic and Cyclic Voltammetry at a platinum electrode in strongly basic (KF) and strongly acidic (SbF₅) media in HF as solvent.It was shown that the first electrochemical step is the formation of a radical which is chemically stable in strongly acidic media probably because of the protonation of pentafluorophenol. The products formed by controlled potential electrolysis were analysed by GCMS. The main products of electrolysis are perfluorocyclohexadienone and dimers of the radical pentafluorophenol. The yield of the various products was evaluated as a function of the acidic level.     

Electrochemical study of the methylcyclopentane oxidation in anhydrous hydrogen fluoride and HF−SbF5 superacid solutions

The electrochemical study of methylcyclopentane (MCPH) oxidation in anhydrous hydrogen fluoride and related superacid media leads to determination of the standard potentials of the MCPH redox couples and to the establishment of the potential acidity diagram of MCPH. Fromtthese results the oxidation by H⁺ ion of MCPH into the carbenium ion MCP⁺ is observed in acidic media: pH<6 or R(H)<?21.9 (pH values are reported on the acidity scale in HF, pH=0 for a molar solution of SbF₅, and the acidity levels are referred to H₂O by means of an R(H) function: for pH=0, R(H) is ?27.9). In HF?SbF₅ mixtures, pH<2.3 or R(H) <?25.6, the protonation of MCPH to form the carbonium ion MCPH₂⁺ has to be taken into account and the acidity constant is determined. In basic media, pH>8.1 or R(H)>?19.8, condensation reactions are enhanced through a radical oxidation state; the disproportionation constant of the dimer (MCP)₂ is determined. Moreover, in the most acidic media, pH<2 or R(H)<?25.9, evidence for the cracking of MCPH through the protolysis of a C?C bond is shown.     

The vibronic and raman spectra of the uranyl ion in anhydrous hydrogen fluoride

The vibronic spectrum of the UO₂²⁺ cation in HF-AsF₅ solution has been recorded in the range 340–450 nm and is much better resolved than corresponding aqueous spectra.     

Solution properties of some pentafluorides and oxide tetrafluorides in anhydrous hydrogen fluoride

Solutions of transition metal pentafluorides, MF₅, M = Nb, Ta, Mo, Re and Os, and oxide tetrafluorides, MOF₄, M = Mo, W and Re, in anhydrous hydrogen fluoride have been prepared. The conductivity and Raman spectrum of the solutions have been recorded. The conductimetric measurements indicate that all the compounds are relatively weak fluoride ion acceptors; the order of Lewis acid strength is OsF₅ > ReF₅ > TaF₅ > MoF₅ > NbF₅ ⪢ ReOF₄ > WOF₄ > MoOF₄. None of the solutions contained sufficient amounts of MF₆⁻ or MOF₅⁻ ions to detect by Raman spectroscopy. The data obtained in this study are discussed, together with similar existing data on other pentafluoride-hydrogen fluoride solutions.     

Reactions of periodate in anhydrous hydrogen fluoride and the partial hydrolysis of iodine heptafluoride

Solutions of sodium periodate or periodic acid in anhydrous hydrogen fluoride contain HOIOF₄ as well as other unidentified fluorine containing species. Partial hydrolysis of iodine heptafluoride yields first IOF₅ and with increased water addition, HOIOF₄, which is dissociated to produce the IO₂F₄⁻ ion. Raman, i.r. and ¹⁹F NMR spectra of this anion have been obtained, and C_2v symmetry has been assigned.     

Reactions in anhydrous hydrogen fluoride Communication 5. Fluoroaminomethylation and fluoroacylaminomethylation of haloolefins

Conclusions The new reaction of conjugated fluoroaminomethylation of chloro and fluoro olefins is described; it may be used for the synthesis of various fluorine-containing amines.For Communications 3 and 4 see Zh. Vses. khim. obshch. im. D. I. Mendeleeva11, 354, 356 (1966).This article is published in accordance with a resolution of the conference of editors-in-chief of journals of the Academy of Sciences of the USSR of July 12, 1962, as a dissertation paper by A. V. Podol'skii.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1575–1581, September, 1966.We thank É. I. Fedin and P. V. Petrovskii for determining and interpreting the spectra.     

Reactions in anhydrous hydrogen fluoride Communication 1. Conjugated halogenation of olefins

Conclusions A method was developed for the synthesis of chlorofluoroalkanes by the conjugated chlorination of olefins in anhydrous HF. The 2-chloroethyl cation formed in the chlorination of ethylene can make an electrophilic attack on benzene with formation of (2-chloroethyl)benzene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1065–1069, June, 1966.     

Disproportionation of bromine and iodine in hydrogen fluoride media

Disproportionation occurs when chlorine, bromine, or iodine are reacted with a hydrogen fluoride solution containing silver fluoride. In each case the reaction product is a halide which is tied up as the insoluble silver salt while the oxidation products are chlorine monofluoride, bromine trifluoride and iodine pentafluoride respectively.     

New developments in the synthesis of lower fluorinated pyridines via diazotization-fluorination of aminopyridines in anhydrous hydrogen fluoride

The isolation and stabilization of elusive 4-fluoropyridine as the hydrochloride salt (54% yield) from fluorodediazoniation of 4-aminopyridine in anhydrous hydrogen fluoride (AHF) is described. Unlike the low yields (0–13%) recently reported from the chlorodediazoniation of 2,6-diaminopyridine and 3-halo-2,6-diaminopyridine, fluorodediazoniation gave high yields (49–62%) of the corresponding 2,6-difluoropyridines. In contrast, benzene analogs, i.e. $\text{m}$-phenylenediamine and 4-chloro-$\text{m}$-phenylenediamine, form only tars under similar fluorination conditions. Vicinal aminohalopyridines, e.g. 3-amino-2-chloropyridine and 2-amino-3,5-dichloropyridine give the corresponding fluorohalopyridine in 49–89% yield. Again, the benzene analogs, i.e. $\text{o}$-chloroaniline and 2,4-dichloroaniline, resist fluorination.     

pH equilibria in anhydrous liquid hydrogen fluoride: The acidity of BF3, PF5, NbF5, TaF5 and AsF5

Fluoride ion concentration in liquid anhydrous hydrogen fluoride, interrelated to hydrogen ion concentration, can be determined by means of a hydrogen electrode. The ionic product of HF ([H⁺][F⁻] = 10^−19·3) is much smaller than had been assumed hitherto. The evaluation of stability constants for the formation of the fluoro complexes of several fluoride ion acceptors is possible by pH titration. PF₅ (PF₅ + F⁻⇌ PF₆⁻; log K_PF6⁻ = 3·85) is a very weak fluoride ion acceptor in AHF. BF₃ (log K_BF4 = 7·26), NbF₅ (log K_NbF6 = 6·88) and TaF₅ (log K_TaF6 = 8·88) are fluoride ion acceptors of moderate strength, and AsF₆ (log K_AsF6 = 16·9) is a quite strong fluoride ion acceptor. The particle As₂F₁₁⁻ appears as intermediate during the formation of AsF₆⁻. In solutions of SbF₅ the hydrogen electrode does not work properly. Fluorosulfonic- and trifluoromethylsulfonic-acids are nonelectrolytes in AHF.