Preparation: Phosphorus pentachloride (PCl5) is usually prepared by the action of an excess of chlorine on phosphorus trichloride.
PCl3 + Cl2 → PCl5
- Phosphorus pentachloride is a yellowish white crystalline solid.
- It sublimes on heating at 473 K and melts at 318 K under pressure.
a. Phosphorus pentachloride dissociates on heating into phosphorus trichloride and chlorine.
PCl5 ↔ PCl3 + Cl2
b. It is violently hydrolysed by water giving phosphorus oxychloride or phosphoric acid depending upon the quantity of water.
- PCl5 + H2O (insufficient of water) → POCl3 + 2HCl
- PCl5 + 4H2O (Excess of water) → H3PO4 + 5HCl
c. It reacts with compounds containing hydroxyl groups forming chloro derivatives. In all these cases, the hydroxyl group is replaced by chlorine.
C2H5OH (Ethyl Alcohol) + PCl5 → C2H5Cl (Ethyl Chloride) + POCl3 + HCl
d. It reacts with metals on heating to give corresponding chlorides.
2Ag + PCl5→2 AgCl + PCl3
PCl5 molecule has trigonal bipyramidal shape in vapour state which arises from sp3d hybridization of phosphorus atom.