Phosphorus V Sulfobromide Thiophosphoryl Tribromide

Of the various methods of preparing phosphorus (V) sulfobromide, experience has shown that the simplest is that of Michaelis. In consists of digesting phosphorus(V) sulfide and phosphorus (V) bromide until the reaction is complete, followed by suitable purification. 

pyrex three-necked flask is fitted with a separatory funnel and a horizontal drying tube attached with rubber stoppers. The drying tube containing phosphorus (V) oxide is connected in a horizontal position to a glass tube elbow inserted in a rubber stopper to allow for pressure changes. 

Thirty-one grams of dry red phosphorus is placed in the flask, and 400 g. of liquid bromine is slowly added through the separatory funnel while the flask is cooled by running tap water over it. Next, 100 g. of phosphorus(V) sulfide is added to the phosphorus(V) bromide, just prepared, and the mass is heated on a water bath (or steam cone) for 2 hours. The flask is then heated more vigorously with a direct flame until its contents are completely liquid. 

Using an all-glass condenser and connections (standard-taper conical-joint connections preferred) the phosphorus (V) sulfobromide is distilled at about 25 mm. pressure, and the crude product boiling between 120 to 130° is collected. The yield of crude product based on red phosphorus used is 80 to 85 per cent. 

If the crude product is a red liquid instead of an orange-yellow solid at room temperature, it is impure, probably owing to excess bromine, and may be purified by the following procedure  

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