Hydrogen halides fluoride

Hydrogen fluoride also effects replacement reactions in organic compounds. For example, carbon tetrachloride yields a mixture of chlorofluoromethanes CCI3F, CCI2F2 and so on. Like all the other hydrogen halides, hydrogen fluoride adds on to olefins, for example ... 

The order of reactivity of the hydrogen halides parallels their acidity HI > HBr > HCl >> HF Hydrogen iodide is used infrequently however and the reaction of alco hols with hydrogen fluoride is not a useful method for the preparation of alkyl fluorides Among the various classes of alcohols tertiary alcohols are observed to be the most reactive and primary alcohols the least reactive... 

The order of hydrogen halide reactivity is HI > HBr >> HCl Hydrogen fluoride IS not effective... 

It is known that the order of acidity of hydrogen halides (HX, where X = F, Cl, Br, I) in the gas phase can be successfully predicted by quantum chemical considerations, namely, F < Cl < Br < I. However, in aqueous solution, whereas hydrogen chloride, bromide, and iodide completely dissociate in aqueous solutions, hydrogen fluoride shows a small dissociation constant. This phenomenon is explained by studying free energy changes associated with the chemical equilibrium HX + H2O + HjO in the solu-... 

Although poly(vinyl fluoride) resembles PVC in its low water absorption, resistance to hydrolysis, insolubility in common solvents at room temperature and a tendency to split off hydrogen halides at elevated temperatures, it has a much greater tendency to crystallise. This is because the fluorine atom (c.f. the chlorine atom) is sufficiently small to allow molecules to pack in the same way as polythene. 

All the hydrogen halides are gaseous at room temperature but hydrogen fluoride liquefies at 19.9°C and 1 atmosphere pressure. The most important chemistry of the hydrogen halides relates to their aqueous solutions. All of the hydrogen halides dissolve in water to give solutions that conduct electric current, suggesting that ions are present. The reactions may be written ... 

Any of the four hydrogen halides can be added to double bonds.The compounds HI, HBr, and HF add at room temperature. The addition of HCl is more difficult and usually requires heat, although HCl adds easily in the presence of silica gel. The reaction has been carried out with a large variety of double-bond compounds, including conjugated systems, where both 1,2 and 1,4 addition are possible. A convenient method for the addition of HF involves the use of a polyhydrogen fluoride-pyridine solution.When the substrate is mixed with this solution in a solvent such as THF at 0°C, alkyl fluorides are obtained in moderate-to-high yields. 

In comparison to PTFE, PVF is easily processable using a variety of techniques used for most thermoplastic materials. It offers good flame retardancy, presumably due to the formation of hydrogen fluoride that assists in the control of the fire. Thermally induced formation of hydrogen fluoride is also a negative factor because of its toxicity. As in the case of PVC, elimination of the hydrogen halide (HF) promotes formation of aromatic polycyclic products that are toxic. 

With halide catalysts of the Friedel-Crafts type (e.g., aluminum chloride or boron fluoride) in the presence of hydrogen halide the formation of the carbonium ion results in the addition of the proton from the promoter to the pi electrons ... 

The polymerization of olefins in the presence of halides such as aluminum chloride and boron fluoride but in the absence of hydrogen halide promoter may also be described in terms of the complex carbonium ion formed by addition of the metal halide (without hydrogen chloride or hydrogen fluoride) to the olefin (cf. p. 28). These carbonium ions are apparently more stable than those of the purely hydrocarbon type the reaction resulting in their formation is less readily reversed than is that of the addition of a proton to an olefin (Whitmore, 18). Polymerization in the presence of such a complex catalyst, may be indicated as follows (cf. Hunter and Yohe, 17) ... 

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