Preparation of Thionyl Chloride

A 1L RBF equipped with a Teflon addition funnel containing 237 g of 65% oleum and condenser is set up and 224.5 g of sulfur dichloride is poured to the RBF, a Teflon magnetic stir bar is added to the solution and strong stirring is started. The addition of the oleum is started with a rate of 1 drop per second while the stirring is of maximum speed. After the addition, the water bath is heated to 75°C and maintained at that temperature for 70 minutes. A gentle reflux 1-2 drops per second should start to occur. The mixture is then fractionally distilled by collecting separately the fraction which comes off at 70-80°C (SOCl2) and 142-152°C (80:20 mixture of HSO3Cl and S2O5Cl2), the first drops of the distillate are discarded. The crude thionyl chloride is purified by distillation from 12 g of quinoline while the distillation is protected from moisture with P2O5 plug. Thereafter the thionyl chloride is distilled from 25 mL of linseed oil in the same way. The thionyl chloride should be after the distillation very pure. The separation of HSO3Cl and S2O5Cl2 is very hard since the boiling points are almost identical.



The reaction apparatus


The mixture after the addition of sulfur trioxide and reflux


Distillation of the first fraction


Purification of the product from quinoline and linseed oil

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