Sulphur Monofluoride, S₂F₂

When dry silver or mercurous fluoride and sulphur are heated together in a vacuum, a gas is evolved which is believed to be Sulphur Monofluoride or Disulphur Difluoride, S₂F₂. The fluoride is a colourless gas with an odour similar to that of sulphur monochloride; it is decomposed by moisture with deposition of sulphur. On keeping, the gas yields a yellow or white deposit, the separation of which is complete after 12 to 14 hours, the gas afterwards appearing to be stable at ordinary temperatures. That sulphur monofluoride is not completely stable towards heat is indicated by molecular weight determinations. Samples prepared from silver fluoride gave the results 93.0, 93.2, 94.6, whilst a sample prepared at a higher temperature from mercurous fluoride gave a molecular weight of 86.

At low temperatures the gas yields a snow-like solid which melts at -105.5° C. The density of the liquid at -100° C. is 1.5. The approximate boiling-point is -99° C.

Sulphur monofluoride may be used in a similar manner to the mono-chloride for the vulcanisation of caoutchouc.