请参考:Ullmann's Encyclopedia of Industrial Chemistry 6.1. Sulfur Fluorides [244], [245] Among the sulfur – fluorine compounds S2F2, SF2 [13814-25-0] and its dimer S2F4 [27245-05-2], SF4 [7783-60-0], S2F10 [5714-22-7], and SF6 [2551-62-4], only two have important industrial applications: SF4 and SF6. Physical properties of S2F2 have been reported since 1923 [246].Sulfur difluoride, SF2, and its dimer S2F4 are not especially stable. Disulfur decafluoride, S2F10 (Mr= 254.11), is extremely toxic, causing the death of rats within 16 – 18 h of exposure to S2F10 vapors at a concentration of 1 ppm. It is a colorless, volatile liquid (mp – 92 °C, bp 29 °C) that does not react with water at ambient temperature. It decomposes at ca. 200 °C: a reaction used in the purification of SF6. 6.1.1. Sulfur Hexafluoride [252] Properties. Discovered in 1900 [260], sulfur hexafluoride (Mr= 146.05) is a colorless, tasteless, incombustible gas (sublimation point –63.9 °C). Practically inert from a chemical and biological standpoint, it does not react with water, caustic potash, or strong acids and can be heated above 500 °C without decomposition. However, at very high temperatures, or in the presence of an electric arc, SF6 slowly decomposes, yielding toxic byproducts including lower fluorides of sulfur. The chemical inertness of SF6 is due to the fluorine shielding of the sulfur atom: the molecule is octahedral, S being covalently saturated by six fluorine atoms. SF6 has a high dielectric strength and a high recombination rate after dissociation by electric discharges 6.1.2. Sulfur Tetrafluoride [267] SF4 (Mr= 108.06) is a colorless, nonflammable gas (mp – 121 °C, bp – 40.4 °C) with a penetrating odor; it is very toxic. It reacts rapidly with water: The high reactivity of SF4 is used to form selectively fluorinated compounds [274]: – CF2– groups from ketones or thiocarbonyl compounds; – CF3 groups from carboxylic acids, esters, anhydrides, or amides; and inorganic fluorides MFx from oxides or sulfides. A concentration of 50 ppm was found to be lethal to one of two animals exposed for four hours; all animals exposed to a concentration of 10 ppm for one hour showed irregular breathing and signs of irritation [275]. 6.4. Phosphorus – Fluorine Compounds [291] Phosphorus trifluoride (Mr= 87.97) is a colorless gas, slowly hydrolyzed by moist air (mp – 151.5 °C, bp – 101.8 °C). Its toxicity is related to its ability, like CO, to form a stable complex with hemoglobin.A mixture of PF3 with oxygen can detonate violently, but activation is necessary (electric spark). Phosphorus pentafluoride (or pentafluorophosphorane), PF5 (Mr= 125.97), has been widely studied. It is a colorless, strongly fuming gas (mp – 93.8 °C, bp – 84.6 °C) that is very hygroscopic and easily hydrolyzable: a slight trace of moisture forms POF3 and HF, and with more water, hydrolysis yields phosphoric acid, with oxyfluorophosphates as intermediates. PF5 behaves as a typical electron-accepting Lewis acid. Adducts are formed with amines, ethers, and nitriles.Exchange reactions may be used to prepare PF5 [292], for example: Other fluorinating agents, such as SbF3 and SbF5, are more convenient. PF5 may also be obtained from PF3, or from the thermal decomposition of sodium hexafluorophosphate between 300 and 1000 °C. Phosphorus Oxyfluoride. Phosphorus oxyfluoride (phosphoryl fluoride) [13478-20-1] (Mr= 103.97), POF3, is a gas at room temperature. It is formed from PF5 by reaction with water; further hydrolysis forms a mixture of fluorophosphoric acids. Halide exchange methods allow preparation of POF3 from POCl3. Fluorophosphoric Acids [296]. Monofluorophosphoric acid [13537-32-1] (Mr= 99.99), H2PO3F, is used as a polymerization catalyst; hydrolysis is complete in dilute solutions: Difluorophosphoric acid [13779-41-4], HPO2F2 (Mr= 101.98), is used as a catalyst. Its potassium salt has been reported to be a stabilizing agent in chloroethylene polymers [298]. Hexafluorophosphoric acid [16940-81-1], HPF6 (Mr= 145.97), The anion is stable and is isoelectronic with SF6; however, heating with mineral acids results in hydrolysis. Dry alkali-metal salts heated to high temperatures decompose according to the equilibrium: Substance PF3 PF5 PCl3 PCl5 PBr3 PBr5 POCl3 PSCl3
Appearance colorless colorless colorless white colorless red/yellow colorless colorless Physcal state gas gas liquid solid liquid solid liquid liquid bp, °C – 101.2 – 84.5 76.1 159 (sublimes) 173.2 > 106 (decomp.) 105.1 125 fp, °C – 151.5 – 93.8 – 93.6 160.5 – 41.5 83.8 (sublimes) 1.25 – 36 Heat of formation, kJ/mol – 918.8 – 1595.8 – 319.7 – 443.5 – 184.5 – 269.9 – 597.1 – 344
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