Properties of hydrogen fluoride

The self-ionisation equilibria or auto-protolysis of liquid FIF are demonstrated in Eq (2.2). The high Hammett acidity function of the anhydrous acid (-Ho=11 compared to HCI can be partly attributed to the formation of stable hydrogen-bonded anions e.g., HF2, H2F3 etc. 

The acidity of anhydrous hydrofluoric acid can be adjusted conveniently over a wide range On addition of alkali metal fluorides the acidity is reduced while the inverse effect is obtained on addition of BF3. In the latter case acidity is enhanced by removal of fluoride ions [Eq (2.3)]  

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TABLE 8.5.1 Physical Properties of Hydrogen Fluoride CAS Registry Number 07664-39-3... 

State tlie two most significant chemical properties of hydrogen fluoride contributing to tlie potential for release. 

Maerker, C., Schleyer, P. v. R., Liedl, K. R., Ha, T. K., Quack, M., Suhm, M. A., 1997, A Critical Analysis of Electronic Density Functionals for Structural, Energetic, Dynamic, and Magnetic Properties of Hydrogen Fluoride Clusters , J. Comput. Chem., 18, 1695. 

C. Maerker, P. von Rague Schleyer, R. Liedl, T. K. Ha, M. Quack, and M. A. Suhm, A critical analysis of electronic density functionals for structural, energetic, dynamic and magnetic properties of hydrogen fluoride clusters. J. Comput. Chem. 18, 1695 1719 (1997). 

The powerful dehydrating property of hydrogen fluoride would cause it to be expected to assist in reactions in which water is a product. Such dehydration reactions would not in the true sense be catalytic. However, as the addition of water in the case of the hydrolysis of esters (Simons and Meunier, 66) has been shown to be catalyzed by hydrogen fluoride, the catalytic powers of hydrogen fluoride are probably involved in the reverse reaction, as a catalyst must necessarily accelerate the reverse reaction if it does so for the forward one. For this reason some of these reactions are included here. 

Considerations of mechanism despite their difficulties are extremely valuable and productive. The discovery of the catalytic properties of hydrogen fluoride for condensation reactions came about from considering the mechanisms of certain organic reactions coupled with a knowledge of the chemical and physical properties of hydrogen fluoride. That fundamental acidity is involved in the catalytic properties of hydrogen fluoride is confirmed by the fact that hydrogen chloride under appropriate conditions can catalyze some of the same reactions (Simons and Hart, 81). 

These solutions are thus less acidic than those of antimony pentafluoride because the H2F+ concentration is lower. PF6 appears to behave as a non-electrolyte and it must be concluded that it is too weak a fluoride ion acceptor to enhance the acid properties of hydrogen fluoride (Dean et al., 1970). The strong proton acid HS03F exhibits no appreciable acid properties in HF (Gillespie and Humphreys, 1970). 

Chem., 18, 1695 (1997). A Critical Analysis of Electronic Density Functionals for Structural, Energetic, Dynamic and Magnetic Properties of Hydrogen Fluoride Clusters. 

Table 8 collects a few results for calculated properties of hydrogen fluoride. Comparison with experiment gives an indication of what accuracy can be achieved in large basis set CCSD and CCSD(T) calculations. 

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