[Chemistry Class Notes] on Phosphorus Trichloride Pdf for Exam

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

Physical 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.

Chemical Properties:

            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.