Disulphur decafluoride

Disulphur decafluoride is thermally less stable than sulphur hexafluoride. Its tendency to react with glass and mercury precludes kinetic investigations in conventional pyrex apparatus, but Trost and McIntosh172 have studied the thermal decomposition in a copper vessel fitted with a diaphragm manometer. Within the experimental error of + 3 % the stoichiometry of the reaction was 

The activation energy of the heterogeneous reaction was estimated to be 39-40 kcaLmole-1. 

The authors suggested a Rice-Herzfeld mechanism of the form 

The choice of reaction (72) as the termination reaction is dictated by the overall order of unity, if reaction (69) is in its first-order pressure region. This is probably true above 200 torr. With the usual approximations the mechanism leads to the rate expression 

Since E12 will be small, 69+ 70-f-F 71 must be about 98 kcaLmole-1. The strength of the S-S bond173,174 should be close to 65 kcaLmole-1. Thus the sum 

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The semi-empirical CNDO/2 method has been applied64 to an analysis of the electronic structure and conformation of disulphur decafluoride. The results, in good agreement with the available experimental data, enable the calculation of the electronic terms which determine the shape of the potential surface and a discussion of the electronic non-equivalence of the axial and equatorial fluorine atoms, the chemical bond strength, and the anomalous S—S bond length in the S2F10 molecule. 

A convenient method for the preparation of telomers of pentafluoro-sulphur iodide, with the general formula SF5(C2F4)nI, has been described.69 The compounds were prepared by the reaction of disulphur decafluoride with equimolar amounts of 1,2-di-iodotetrafluoroethylene at 150 °C in an autoclave, with the simultaneous injection of tetrafluoroethylene ... 

Disulphur decafluoride. Made in the UK in 1934. High toxicity, no odour. In rhesus monkey, was one tenth as toxic as phosgene. 

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