Thiothionyl fluoride
# Thiothionyl fluoride

Thiothionyl fluoride is a chemical compound of fluorine and sulfur, with the chemical formula $S=SF_2.$ It is an isomer of disulfur difluoride (difluorodisulfane) F−S−S−F.

## Preparation

Thiothionyl fluoride can be obtained from the reaction between disulfur dichloride with potassium fluoride at about 150 °C or with mercury(II) fluoride at 20 °C.

    $S_2Cl_2$ + 2 KF → $S=SF_2$ + 2 KCl

Another possible preparation is by the reaction of nitrogen trifluoride with sulfur.

    $NF_3$ + 3 S → $S=SF_2$ + NSF

It also forms from disulfur difluoride when in contact with alkali metal fluorides.

$S=SF_2$ can also be synthesized with the reaction of potassium fluorosulfite and disulfur dichloride:

    2 $KSO_2F$ + $S_2Cl_2$ → $S=SF_2$ + 2 KCl + 2 $SO_2$

## Properties

Thiothionyl fluoride is a colorless gas. At high temperatures and pressures, it decomposes into sulfur tetrafluoride and sulfur.

    2 $S=SF_2$ → $SF_4$ + 3 S

With hydrogen fluoride, it forms sulfur tetrafluoride and hydrogen sulfide.

    $S=SF_2$ + 2 HF → $SF_4$ + $H_2S$

It condenses with sulfur difluoride at low temperatures to yield 1,3-difluoro-trisulfane-1,1-difluoride.

    $S=SF_2$ + $SF_2$ → $FS−S−SF_3$
