Sulfur fluorides and oxofluorides

Physical appearance and Colourless Yellow solid Colourless Colourless Colourless Colourless Colourless 

The structure of SF4, 15.26, is derived from a trigonal bipyramid and can be rationalized in terms of VSEPR theory. The S—F and S—F q bond distances are quite different (Table 15.5). Oxidation by O2 in the absence of a 

is related to that of SF4, but with S—F x and S—F, bond distances that are close in value. 

Among the sulfur fluorides, SFg, 15.28, stands out for its high stability and chemical inertness. It can be made by burning S in F2, and is commercially available, being widely used as an electrical insulator. Its lack of reactivity (e.g. it is unaffected by steam at 770 K or molten alkalis) is kinetic rather than thermodynamic in origin. The value of A G° for reaction 15.53 certainly indicates thermodynamic spontaneity. The bonding in SF5 was discussed in Section 4.7. 

The preparation of SFg from S and F2 produces small amounts of S2F10 and the yield can be optimized by controlling the reaction conditions. An alternative route is reaction 15.54. Selected properties of S2F10 are given in Table 15.5. 

Both isomers are unstable with respect to disproportionation into SF4 and S, and are extremely reactive, attacking glass and being rapidly hydrolysed by water and alkali (e.g. equation 16.54). 

The preparation of SFg from S and F2 produces small amounts of S2F10 and the yield can be optimized by 

Although unaffected by water, SO2F2 is hydrolysed by concentrated aqueous alkali. A series of sulfuryl fluorides is known, including FSO2OSO2F and FSO2OOSO2F. The latter compound is prepared by reaction 16.65 fluorosulfonic acid (see Section 9.8) is related to the intermediate in this reaction. 

Sulfur tetrafluoride, SF4, is best prepared by reaction 16.55. It is commercially available and is used as a selective fluor-inating agent, e.g. it converts carbonyl groups into CF2 groups without destroying any unsaturation in the molecule. Representative reactions are shown in Fig. 16.13. SF4 hydrolyses rapidly and must be handled in moisture-free conditions. 

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Sulfur forms two main series of oxohalides, the thionyl dihalides OS X2 and the sulfuryl dihalides 02S X2. In addition, various other oxofluorides and peroxofluorides are known (p. 688). Thionyl fluorides and chlorides are colourless volatile liquids (Table 15.14) OSBt2 is rather less volatile and is orange-coloured. 

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