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Phosphorus Trichloride

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Last updated date: 17th Apr 2024
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What is Phosphorus Trichloride?

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:

  • It reacts with water violently and forms phosphorus acid.


            PCl3 + 3H2O → H3PO3 + 3HCl


  • It combines with oxygen to form phosphorus oxychloride.


2PCl3 + O2 → 2POCl3


  • It reacts with sulphur trioxide to form phosphorus oxychloride.


PCl3 + SO3 → POCl3 +SO3


  • It reacts with halogens and sulphur monochloride to form phosphorus pentachloride.


PCl3 + Cl2 → PCl5 + SO2


PCl3 + S2Cl2 → PCl5 + 2PSCl3


  • It reacts with organic compounds that contain OH groups and substitute this group with the chlorine.


3CH3COOH + PCl3 → 3CH3COCl + H3PO3


  • It readily oxidises to the phosphorus derivatives.

  • It undergoes substitution reactions both in organic and inorganic reactions.


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.

FAQs on Phosphorus Trichloride

1. Explain the structure of phosphorus trichloride.

Phosphorus in PCl3 undergoes sp3 hybridization. Three of the sp3 hybrid orbitals overlap with P-orbitals of chlorine to form three P-Cl sigma bonds while the fourth sp3 hybridised orbital contains a lone pair of electrons. Therefore, PCl3 has a pyramidal structure. The bond angle is 100.4 degrees in PCl3. The structure of PH3 and PCl3 is similar, but the bond angle in both the compounds is different. In PCl3 the bond angle is more than the PH3 due to steric hindrance caused by the larger sized chlorine atom.

2. Write five physical properties of phosphorus trichloride.

Five physical properties of phosphorus trichloride are given below:

  • It is a colourless oily liquid.

  • 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.

3. Write five chemical properties of phosphorus trichloride.

Five chemical properties of phosphorus trichloride are as follows:

  • It gives a violent reaction with water to form phosphorus acid.

  • It readily combines with oxygen to give phosphorus oxychloride.

  • It’s reaction with sulphur trioxide gives us phosphorus oxychloride.

  • Phosphorus pentachloride is formed when phosphorus trichloride reacts with halogens and sulphur monochloride.

  • Phosphorus pentachloride is formed when phosphorus trichloride undergoes further chlorination.

4. What happens when phosphorus trichloride reacts with water?

Phosphorus trichloride reacts violently with water. The chlorine from phosphorus trichloride replaces the OH- group from water to form Hydrochloric acid or HCl. Phosphoric acid is also formed as the end result of this reaction.

5. What are the various uses of phosphorus trichloride?

The various uses of phosphorus trichloride are as follows:

  • It is a very important substance used in textile finishing.

  • It is also used to make various chemical substances such as catalysts, pesticides, dyestuffs and plasticizers.

  • It is also used in gasoline additives.

  • Phosphorus trichloride is also used to manufacture phosphorus oxychloride which is further used in manufacture of various other useful chemicals.

6. When was phosphorus trichloride first prepared?

In the year of 1808, phosphorus trichloride was first prepared by by the French Chemists Joseph Louis Gay-Lussac and Louis Jacques Thénard. This was by heating Hg2Cl2 (Calomel) with phosphorus. In that very same year later, phosphorus trichloride was produced again by an English chemist named Humphry Davy. This was done by him by burning phosphorus in the presence of chlorine gas.