Antimony pentahalides

This demonstration marked the beginnings of the CFC industry as we know it today. Continuous processes were developed wherein a chlorocar-bon and HF were fed to a reactor containing antimony pentahalide, usually dissolved in the fluorinated reaction intermediates. Under reaction conditions, pentavalent antimony is somewhat unstable, reverting back to the trivalent state and chlorine. Industry practice is to feed chlorine to oxidize trivalent antimony back to the pentavalent state. In its simplest form the exchange reaction with CCI4 can be written as shown in Eqs. (4) and (5). Over the years, several improvements to such processes have been made... 

Phosphorus, Arsenic, and Antimony Pentahalides and Aluminum Trichloride... 

The arsenic and antimony pentahalides EX5 (E group 15 element As or Sb X = F or Cl) are strong, irreversible oxidants the gas AsFs has little been used, but SbCF and SbFs are commercially available, very air-sensitive liquids which are used in dry and deoxygenated dichloromethane and liquid sulfur dioxide respectively. SbCls is easier to handle than SbFs which gives the dangerous HF by reaction with moist air. Moreover, SbCls is conveniently used in dichloromethane whereas SbFs is best used in liquid SO2. On the other hand, the side products (halogenation) are more frequently encountered with SbCls than with SbFs. The redox process follows ... 

Yakobson, G. G., Furin, G. G. Antimony pentahalides as catalysts of Friedel-Crafts type reactions. Syrrf/jes/s 1980, 345-364. 

The reaction proceeds through the antimony pentahalide salts, with the major reactants believed to be a mixture of SbClsFs and more highly fluorinated halides including SbFj. 

Antimony trioxide requires the presence of a small quantity of a halogen containing material. During combustion antimony pentahalides are formed, which are extremely powerful free-radical scavengers. They remove the active species from the combustion source, and so inhibit combustion effectively. 

Sixteen pentahalides could conceivably exist for combinations of P, As, Sb, and Bi with F, Cl, Br, and I. However, several of these possibilities are unknown, and others are of little importance. None of the elements forms a stable pentaiodide, but all of the pentafluorides are known. Phosphorus forms a pentachloride and a pentabromide, whereas antimony forms a pentachloride. As with the discussion of the trihalides, most of the discussion presented will center on the phosphorus compounds. 

Thio- and selenohalides MEX3 (E = S, Se) are accessible by the reaction of antimony chalcogenides with pentahalides at rt in CS2. NbSCls can also be conveniently obtained by reacting the pentachloride with hexamethyldisilathiane... 

BTF is prepared industrially from toluene in two synthetic steps 1) free radical perchlorination of the methyl group, followed by 2) fluorine/chlorine exchange of the three chlorine atoms with anhydrous hydrogen fluoride (Scheme 1). The chlorination step may be catalyzed by light of suitable wavelength (UV) and is conveniently carried out in the liquid phase. The fluoride/chloride exchange can be catalyzed by the presence of metal halide compounds, such as pentahalide (Cl, F) salts of antimony and molybdenum, and is effected under a variety of... 

Both trihalides and pentahalides are known for arsenic, antimony, and bismuth. The 12 possible trihalides, all of... 

The decreasing stabUity of the +5 oxidation state is shown by the fact that all 16 EX3 compounds (E = P, As, Sb, Bi X = F, Cl, Br, I) are formed, but only phosphorus forms pentahalides with all four halogens. Arsenic and antimony form only the pentafluoride and pentachloride, whereas bismuth forms only the pentafluoride. Of the pentafluorides of the lower three pnicogens, only ASF5 is trigonal bipyrami-dal. SbFj and BiFj are polymers of EF octahedra held together by bridging fluorine atoms. 

Bismuth and antimony tend to be metallic, readily losing electrons to form cations. Although these elements have five valence electrons, so much energy is required to remove all five that no ionic compounds containing Bi or ions are known. Three pentahalides (Bip5, SbCls, and SbF5) are known, but these are molecular rather than ionic compounds. 

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