Laboratory Preparation of Phosphorus Trichloride - QS Study
QS Study

Preparation: Phosphorus Trichloride (PCl3) is prepared by heating white phosphorus in a current of dry chlorine.

P4 + 6Cl2 → 4PCl4

Dry white phosphorus is placed in the retort and gently heated on a water bath. A current of pure, dry chlorine is led over the phosphorus. The phosphorus trichloride formed being volatile distils over and is collected in a water cooled receiver.

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Fig: Laboratory Preparation of PCl3

The phosphorus trichloride obtained as above contains some PCl5 as impurity. This is removed by distilling the PCl3 over white phosphorus.

 

Physical properties

  • Colourless low boiling liquid
  • It fumes in moist air
  • It has pungent odour.

Chemical Properties

a. It is violently hydrolysed by water giving phosphorus acid and hydrochloric acid gas.

PCl3 + 3 H2O → 3HCl + H3PO3

In a similar manner it reacts with organic compounds containing hydroxyl (OH) group, such as acids and alcohols.

  • PCl3 + 3CH3 COOH (Acetic Acid) → 3CH3COCl + H3PO3 (Acetyl Chloride)
  • PCl3 + 3C2H5OH (Ethyl alcohol) → 3 C2H5Cl + H3PO3 (Ethyl Chloride)

b. It reacts with chlorine or sulphuryl chloride forming phosphorus pentachloride.

  • PCl3 + Cl2 → PCl5
  • PCl3 + SO2Cl2 → PCl5 + SO2

c. It readily combines with oxygen forming phosphorus oxychloride

2PCl3 + O2 →2POCl3

d. It reacts with SO3 to form phosphorus oxychloride and SO2

SO3 + PCl3 → POCl3 + SO2

 

Structure: PCl3 molecule has a pyramidal shape, which arises from sp3 hybridization of phosphorus atom. One of the tetrahedral positions is occupied by a lone pair of electrons.

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