Phosphoryl Halides Phosphorus Oxyhalides

All the phosphoryl halides, POX3, have now been characterised (4.307), as well as mixed species such as POF2CI, POFCI2, POBrCl2, etc. The phosphoryl halides are all toxic and reactive. They may be formed by oxidation of the appropriate trihalide and all are hydrolysed by water. The iodide has also been prepared (4.322) below. 

Phosphoryl fluoride is obtainable by hydrolysis of PF5 or hexafluorophosphates (4.240), or by dropwise addition of fluorosulphonic acid to an excess of P4O10 (4.310). 

Phosphoryl chloride (phosphorus oxychloride), POCI3, mp = 1.25°C, bp = 105.8°C, J. = 2.39 D, p = 1.645 g/cc, is a clear colourless fuming liquid which can be made by the careful oxidation of the trichloride with air, oxygen or oxidising agents such as potassium chlorate (4.311) and others. It can be obtained by reacting the pentachloride with boric acid (4.312), with alcohols (4.313), oxides of nitrogen (4.314), sulphur dioxide (4.315) or phosphorus pentoxide (4.47). The reaction with oxalic acid (4.316) is a convenient laboratory method. 

Direct oxidation of the chloride is the usual commercial method of making phosphoryl chloride. Other commercial processes involve the reaction between phosgene and iron phosphate (4.317), but the simple reaction (4.318) has not yet been made commercially viable. 

Phosphoryl chloride is a non-protonic solvent, but its properties show a remarkable resemblance to those of water (Table 4.25). The low electrical conductivity of both solvents indicates only slight dissociation (4.319), (4.320). The extensive system of hydrogen bonds, characteristic of water, is of course absent in phosphoryl chloride. 

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