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Friday, August 16, 2013

Preparation of Phosphorus Pentasulfide - A Thionation Reagent - Lu Le Laboratory

Phosphorus pentasulfide is the inorganic compound with the formula P4S10. This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities.

 In organic chemistry P4S10 is used as a thionation reagent. Reactions of this type require refluxing solvents such as benzene, dioxane or acetonitrile with P4S10 dissociating into P2S5. P2S5 can be trapped for example as the pyridine complex. Ketones are converted to thioketones. In esters, imides and lactones the oxygen atom can also be replaced by sulfur. With amides the reaction product is a thioamide. With 1,4-diketones the reagent forms a thiophene. Compared to the better known Lawesson's reagent P4S10 suffers from reduced yields.   (Wikipedia)


1.     Red phosphorus (pre-dried) : 1.6722 g

2.     Sulfur (resublimed) : 4.3278 g



1.     A Hot plate

2.     A crucible with a cover

3.     Spatula

4.     Mortar and pestle


1.     Add 1.6722g red phosphorus powder and 4.3278 g resublimed sulfur in a crucible (with a cover).

2.     Heat the crucible genteelly to about 300℃[1] and leave it for 5 minutes.


3.     Cool the crucible in a desiccator.

4.     Scratch the solid from the crucible and smash it into powder with a mortar and pestle.[2]


 It is a greenish-yellow powder

5.     Preserve it in an air-tight vessel.



[1] Don’t open the cover before you cool the crucible to room temperature or it may cause fire and produce toxic gases. Once it burns, use dry sand or dry powder extinguisher. Don’t use water to extinguish fire or it may cause explosion.


[2] This procedure must be done in a hood or a ventilate area. If high concentration of hydrogen sulfide (with an odor of rotten egg) is inhaled, it will rapidly absorbed through the lung into blood. It may cause coma and may be rapidly fatal.

[3] This product is highly flammable and very toxic to aqueous organisms

[4] Must see the MSDS of phosphorus pentasulfide before you handle it.

Experimental Record

Weight of Phosphorus Pentasulfide
4.4102 g
Theoretical Weight of Phosphorus Pentasulfide
6.0000 g
(4.4102 g) / (6.0000 g) x 100%

= 73.50%

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