308 GROUP VI
SOC1 2 + 2H 2 O ^ 4H+ + SOr + 2C1~
Hence on warming, sulphur dioxide is evolved.
Sulphur oxide dichloride is used as a chlorinating agent in organic
chemistry, for example in the preparation of acid chlorides:
CH 3 COOH + SOC1 2 -> CH 3 COC1 + SO 2 f + HClt
The advantage of the method, readily seen from the equation,
is that the other products of the reaction are gaseous and escape.
Hence equimolar quantities of reactants are used.
A somewhat similar reaction is the power of sulphur oxide
dichloride to remove water of crystallisation from hydrated chlorides,
the hydroxyl groups of the water molecule reacting as do those in
the acid molecules in the above reaction.
The action is a general one and may be written thus:
MCln.xE 2 O + xSOC! 2 -> MCI, + xSO 2 t 4- 2xHClT
The reaction provides a valuable method of preparing anhydrous
chlorides of metals. It has been used to prepare the anhydrous
chlorides of copper(II), zinc, cadmium, chromium(III), iron(III),
cobalt(II) and nickel.
In both reactions above, the oxide dichloride is refluxed with
the acid or the hydrated chloride; the sulphur dioxide and hydrogen
chloride pass off and any unused sulphur oxide dichloride is dis-
tilled off in vacua.TESTS FOR SULPHUROxidation of a sulphur compound with concentrated nitric acid
yields sulphuric acid or a sulphate, which can be tested for with
barium chloride. This can be used to estimate the sulphur.QUESTIONS
- How would you obtain a sample of pure ozone? Account for
the conditions used in your method of preparation. What is the
arrangement of oxygen atoms in an ozonide and what evidence
would you cite in support of the structure you suggest?
(L,A) - Comment on and, where you are able, suggest reasons for the
following observations: