Sulfur, Selenium, and Tellurium Hexafluorides

The preparation of the hexafluorides of sulfur, selenium, and tellurium consists in passing gaseous fluorine over the elementary substances. 

The sulfur, selenium, or tellurium in a moderately finely divided state is placed in a copper tube provided with an outlet and inlet. The outlet is connected to a train consisting of a trap cooled in a concentrated hydrochloric acid-ice mixture and then another immersed in liquid air or a solid carbon dioxide-alcohol mixture. Fluorine (synthesis 51) is passed into the inlet at the rate of 1 to 3 1. per hour. The reaction proceeds smoothly. The lower fluorides are condensed to a large extent in the hydrochloric acid-ice cooled trap, and the material collected in the liquid air or solid carbon dioxide trap consists principally of hexafluorides. 

Sulfur hexafluoride may be passed through water, dried over phosphorus pentoxide, and further purified by repeated sublimation of the solid at low temperatures and pressures. Selenium and tellurium hexafluoride are best purified by repeated sublimation at the temperature of solid carbon dioxide, care being taken to cause the middle fraction to melt after each sublimation. The less volatile impurities consist principally of lower fluorides (tetrafluorides). 

All of these hexafluorides are white solids, colorless liquids, or colorless gases. 

Submitted by J. H. Balthis, Jb., and John C. Bailab, Jr. Checked by Fbedebic B. Duttonf 

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