Hydrogen fluoride, liquid conductivity

Some liquids other than water can serve as ionizing solvents, with the power of dissolving electrolytes to give electrically conducting solutions. These liquids include hydrogen peroxide, hydrogen fluoride, liquid am-... 

Simons reports that carboxylic acids dissolved in liquid hydrogen fluoride produce conducting solutions ... 

The addition of hydrogen fluoride to acetylene has been widely investigated because the initial product, vinyl fluoride, is a commercially important monomer Acetylene reacts with hydrogen fluoride in the liquid phase in the absence of catalyst to give vinyl fluoride and 1,1 -ditluoroethane in modest yields [7 ], but better results are achieved by conducting the addition with various additives or catalysts... 

Hydrofluoric acid in contact with water behaves anomalous when compared to the heavier halogens. The hydrogen-fluoride bond is relatively strong and ion pairs of the type H3 0+F exist rather than free hydronium ions [10]. Anhydrous HF is an electrically conducting liquid (3HF = H2F+ + HF2 occurs) with a normal boiling point of 19.5 °C. Scheme (1) summarizes the most important forms, the standard potentials in acidic aqueous media, and typical applications of fluorine. 

The electrofluorination of acetophenone and benzophenone takes place in anhydrous HF and in the presence of solvents such as chloroform and acetonitrile [38]. The fluorination of the aromatic rings occurred to various extent. Further uses of anhydrous hydrogen fluoride as a liquid environment for electrofluorination processes have been reported, for example, by Matalin etal. [39]. In particular, systems with low conductivity in liquid hydrogen fluoride and nonselective processes have been studied and optimized. The fluorination of benzene and halobenzenes in the presence of Et4NF—(HF) in an undivided cell has been studied by Horio et al. [40] Cathodic dehalogenation is observed to accompany the anodic fluorination process. 

An important industrial process for the conversion of organic precursors to fully fluorinated derivatives (perfluo-rocarbon compounds) is the Simons Process. The Simons Process [1-9] uses an electrochemical cell to oxidize per-hydro-organic materials, at a nickel anode, to their perfluoro-relatives. The electrolyte for that process is liquid anhydrous hydrogen fluoride in which sodium fluoride, or other ionizing solutes, are dissolved (the latter, to provide for electrical conductance). 

If F2 were formed by the electrolysis of an aqueous fluoride solution, it would immediately oxidize water to oxygen. For this reason, fluorine is prepared by electrolyzing liquid hydrogen fluoride containing potassium fluoride to increase its conductivity, at about 70°C (Figure 21.17) ... 

Liquid ammonia appears to be an exception to this rule. The conductivities of solutions of acids and bases are high, but so are the conductivities of other electrolyte solutions in this solvent. An explaination has been advanced from a structural point of view all units involved in frequent proton transfer reactions are not fully coordinated and polar such as H3O+, H2O and OH in water or H2F+, HF and F in liquid hydrogen fluoride. In contrast the NH4+ ion produced in liquid ammonia is symmetrical and non-polar and release of a proton is not easily possible (the NH4+-ion is a very weak Bronsted acid, while the HaO -ion is the strongest Bronsted acid in water). 

Liquid hydrogen cyanide has a limited liquid range, in which the degree of association is apparently similar to that of the hydrogen halides HX, where X = Cl, Br, I. On the other hand it has in common with liquid hydrogen fluoride a high dielectric constant and it has been used in the study of conductivities in non-aqueous solutions . 

Strongly acidic media. A difficulty arose from the fact that mixing benzene with pure inorganic acids as a solvent generally leads to two-phase systems. In spite of this drawback, which reduces the conductivity of the system, Shepard and Dannels were able to polymerize benzene in hydrogen fluoride [99]. With the position of the Pt electrodes chosen to obtain the highest conductivity (anode in contact with the liquid-liquid interface) a dark, infusible, insoluble and insulating polymer was deposited on the anode, but its structure was not elucidated. 

Chloro-aluminate ionic liquids promote the carbonylation of alkylated aromatic compounds, but fails in the case of oxygenated aromatics. Aldehyde yields of formylation in the acidified neutral ionic liquids were generally similar compared to reactions conducted in HF as solvent/catalyst (cf Table 2.2). The increase in aldehyde yields with the use of extended alkyl chain lengths of the cationic part of the melt, may be due to improved CO solubility. HF/BFs-acidified neutral ionic liquids showed both increases in para-selectivity compared to HF as solvent and catalyst. Formylation of anisole and toluene, but not of phenol in the neutral ionic liquids resulted in increased secondary product formation in comparison with hydrogen fluoride used as solvent/catalyst. This difference in behaviour is not understood at present, but suggests that phenol is a good substrate for formylation in this medium, particularly with the development of a system catalytic with respect to HF/BF3 in mind. 

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