What is Phosphorus Trichloride Definition Structure Preparation Reactions and Applications
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 PCl3 Properties Structure and Uses
1. What is phosphorus trichloride?
Phosphorus trichloride is a colorless to pale yellow covalent liquid with the chemical formula PCl3, consisting of one phosphorus atom bonded to three chlorine atoms. It is an important industrial chemical used mainly in the production of organophosphorus compounds.
- Molecular formula: PCl3
- Molar mass: 137.33 g/mol
- State at room temperature: Liquid
- Highly reactive with water (hydrolyzes)
2. What is the chemical formula and structure of phosphorus trichloride?
The chemical formula of phosphorus trichloride is PCl3, and it has a trigonal pyramidal molecular geometry. According to VSEPR theory, phosphorus has three bonding pairs and one lone pair of electrons.
- Central atom: Phosphorus (P)
- Bond pairs: 3 P–Cl single bonds
- Lone pairs: 1 on phosphorus
- Electron geometry: Tetrahedral
- Molecular shape: Trigonal pyramidal
3. Is phosphorus trichloride polar or nonpolar?
Phosphorus trichloride (PCl3) is a polar molecule because it has a trigonal pyramidal shape with a lone pair on phosphorus. The P–Cl bonds are polar due to electronegativity differences, and their dipole moments do not cancel out.
- Electronegativity difference between P and Cl creates bond polarity.
- Asymmetrical trigonal pyramidal geometry prevents dipole cancellation.
- Net dipole moment makes the molecule polar.
4. How is phosphorus trichloride prepared?
Phosphorus trichloride is prepared by the direct reaction of white phosphorus with chlorine gas. The balanced chemical equation is:
P4(s) + 6Cl2(g) → 4PCl3(l)
- Reactants: White phosphorus and dry chlorine gas
- Controlled supply of chlorine prevents formation of PCl5
- Exothermic reaction
5. What happens when phosphorus trichloride reacts with water?
Phosphorus trichloride reacts with water to form phosphorous acid and hydrochloric acid. The balanced hydrolysis reaction is:
PCl3(l) + 3H2O(l) → H3PO3(aq) + 3HCl(aq)
- Product 1: Phosphorous acid (H3PO3)
- Product 2: Hydrochloric acid (HCl)
- Reaction is vigorous and releases heat
6. What is the oxidation state of phosphorus in phosphorus trichloride?
The oxidation state of phosphorus in PCl3 is +3. Each chlorine atom has an oxidation state of −1, and since there are three chlorine atoms, the total negative charge is −3.
- Let oxidation state of P = x
- x + 3(−1) = 0
- x − 3 = 0
- x = +3
7. What are the uses of phosphorus trichloride?
Phosphorus trichloride (PCl3) is mainly used as an intermediate in the manufacture of organophosphorus compounds and other phosphorus chemicals. Major uses include:
- Production of phosphites and phosphonates
- Manufacture of pesticides and herbicides
- Preparation of phosphorus oxychloride (POCl3)
- Synthesis of plasticizers and flame retardants
8. What is the difference between phosphorus trichloride and phosphorus pentachloride?
The main difference between phosphorus trichloride and phosphorus pentachloride is that PCl3 contains phosphorus in the +3 oxidation state, while PCl5 contains phosphorus in the +5 oxidation state.
- PCl3: Trigonal pyramidal shape, liquid at room temperature
- PCl5: Trigonal bipyramidal (gas) or ionic solid form, solid at room temperature
- PCl3 forms phosphorous acid on hydrolysis
- PCl5 forms phosphoric acid on complete hydrolysis
9. Is phosphorus trichloride ionic or covalent?
Phosphorus trichloride (PCl3) is a covalent compound because it consists of shared electron pairs between phosphorus and chlorine atoms. Both phosphorus and chlorine are nonmetals, which typically form covalent bonds.
- Type of bonding: Polar covalent
- Discrete molecular structure
- Low melting and boiling points compared to ionic compounds
10. How does phosphorus trichloride react with excess chlorine?
Phosphorus trichloride reacts with excess chlorine to form phosphorus pentachloride. The balanced reaction is:
PCl3(l) + Cl2(g) → PCl5(s)
- Chlorine acts as an oxidizing agent
- Oxidation state of phosphorus increases from +3 to +5
- Reaction is used to prepare PCl5 in the laboratory
