GROUP VI 307
Diselenium dichloride acts as a solvent for selenium. Similarly
disulphur dichloride is a solvent for sulphur and also many other
covalent compounds, such as iodine. S 2 C1 2 attacks rubber in such a
way that sulphur atoms are introduced into the polymer chains of
the rubber, so hardening it. This product is known as vulcanised
rubber. The structure of these dichlorides is given below:
X = S or Se (cf. H 2 O 2 , p. 279).
Sulphur and tellurium form a chloride of formula XC1 2. Sulphur
dichloride SC1 2 is a red liquid at room temperature whilst the
corresponding tellurium compound is a black solid.
A number of bromides and iodides are known but there are no
sulphur iodides.Halide oxides
A number of halide oxides are formed by sulphur and selenium
but only one is considered here.
SULPHUR DICHLORIDE OXIDE, THIONYL CHLORIDE, SOC1 2
This is an important laboratory reagent and has the structure shown
below :
a
aIt is prepared by heating together phosphorus pentachloride and
a sulphite, for example calcium sulphite :
2PC1 5 + CaSO 3 -» 2POC1 3 + CaCl 2 4- SOC1 2The oxide dichloride, b.p. 351 K, is separated from the less volatile
phosphorus oxychloride by a fractional distillation.
Sulphur oxide dichloride is a colourless liquid which fumes in
moist air. It is hydrolysed by water to give a mixture of sulphurous
hydrochloric acids :