Phosphorus forms two types of halides:
1) Phosphorus trihalide (PX3). The covalency of phosphorus in trihalides is 3, and
2) Phosphorus pentahalide (PX5). The covalency of phosphorus in pentahalide is 5.
Phosphorus trichloride is one of the most common phosphorus halides, which is an inorganic compound made up of one phosphorus and three chlorine atoms. It exists in a liquid state. It is poisonous and volatile in nature. Phosphorus trichloride is a very reactive compound. It shows explosivity when it reacts with water.
The IUPAC name of phosphorus trichloride is Trichlorophosphane. The other names by which phosphorus trichloride is known as Phosphorus(III) Chloride and Phosphorus chloride.
Phosphorus trichloride cannot be obtained from nature in its natural form. It is obtained from the synthesis of organic substances. Phosphorus trichloride is very toxic and corrosive in nature, hence, it should not come in direct contact with eyes and skin. It also should not be directly inhaled or ingested. Phosphorus trichloride is also a very important and necessary industrial chemical and hence is used in manufacture of other important chemicals.
Phosphorus Trichloride Formula
Phosphorus trichloride chemical formula is PCl3. The hybridization of phosphorus in PCl3 is sp3. PCl3 has a trigonal bipyramidal shape due to its sp3 hybridization. The bond angles of this structure are less than 109 degrees.
Phosphorus Trichloride Structure
Chemical formula for phosphorus trichloride is PCl3. In Phosphorus trichloride structure PCl3, three sp3 hybrid orbitals of phosphorus overlap with p-orbitals of chlorine to form three P-Cl sigma bonds while the fourth sp3 hybrid orbital contains lone pair of electrons. PCl3 has a pyramidal structure as shown below.
Phosphorus Trichloride Preparation
It can be prepared by passing dry chlorine gas over overheated white phosphorus. The vapours of phosphorus trichloride distil over and are collected in receivers cooled by water.
P4 + 6Cl2 → 4PCl2
It can also be obtained by the reaction of thionyl chloride with the white phosphorus.
P4 + 8SOCl2 → 4PCl3 +4SO2 + S2Cl2
Phosphorus Trichloride Properties
It is a colourless oily liquid.
It might be yellowish in colour sometimes.
It is constantly fuming liquid in the moist air.
Its boiling point is 347 K.
Its melting point is 161 K.
It has a high pungent odour, kind of similar to the hydrochloric acid.
It has a molar mass of 137.33g/mol.
It has a density of 1.574 g/cm3
It has a vapour pressure of 13.3kPa.
It has a refractive index of 1.5122.
It’s dipole moment is 0.97D.
PCl3 + 3H2O → H3PO3 + 3HCl
2PCl3 + O2 → 2POCl3
PCl3 + SO3 → POCl3 +SO3
PCl3 + Cl2 → PCl5 + SO2
PCl3 + S2Cl2 → PCl5 + 2PSCl3
3CH3COOH + PCl3 → 3CH3COCl + H3PO3
Uses of Phosphorus Trichloride PCl3
It is widely used in organic chemistry as an important regent to replace the hydroxyl group by chlorine atom.
It is used for making phosphorus oxychloride by oxidising it with oxygen.
It is used for production of phosphate ester insecticides.
It is used in the production of chlorinated compounds like phosphorous penta chloride, phosphoryl chloride, thiophosphoryl chloride and pseudohalogens.
Did you know?
Phosphorus trichloride can act as a nucleophile. Due to the presence of one lone pair it can donte this pair to the electron deficient compound.
PCl3 can also act as an electrophile. Due to the presence of an empty d orbital it can accept electrons from electron rich compounds and expands its valency to 5.
Reactions including PCl3 generally undergo redox reactions.
PCl3 is highly toxic in nature.
PCl3 violently reacts with water and produces large amounts of heat.
PCl3 causes irritation to eyes, skin and respiratory system.