What Is Phosphorus Pentachloride Definition Structure Preparation Reactions and Uses
Phosphorus pentachloride is a greenish-yellow crystalline solid, It is decomposed by water to form hydrochloric acid and phosphoric acid with the release of heat energy. It can also be prepared by the action of dry chlorine on phosphorus trichloride. The chemical formula for phosphorus pentachloride is PCl5. In a solid state, it exists as PCl4PCl4+PCl6PCl6-.
Phosphorus pentachloride vaporizes without dissociation in an atmosphere of phosphorus trichloride or chlorine gas. The dissociation equilibrium is shifted to the left side by the presence of the product.
Structure of Phosphorus Pentachloride
The hybridization in phosphorus pentachloride is sp3d and it has a trigonal bipyramidal geometry in gaseous and liquid states. It has two axial P−Cl bonds and three equatorial P−Cl bonds.
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Properties of Phosphorus Pentachloride
Uses of Phosphorus Pentachloride (PCl5)
It is used as a chlorinating agent.
It is used for the manufacture of penicillin and cephalosporin in the pharmaceutical industry.
Used to produce acid chlorides.
Used as a catalyst in the manufacture of acetyl cellulose and also a catalyst for condensation reactions and cyclization.
Methods of Preparation of Phosphorus Pentachloride (PCl5)
P4 + 10SO2Cl2 → 4PCl5 + 10SO2
P4 + 10Cl2 → 4PCl5
PCl3 + Cl2 → PCl5
Chemical Properties of Phosphorus Pentachloride (PCl5)
Phosphorus pentachloride dissociates as: PCl5 ⇌ PCl3 + Cl2
Reaction with water: PCl5 + 4H2O → H3PO4 + 5HCl
Reaction with metal: Zn + PCl5 → ZnCl2 + PCl3
Reactions with phosphorus pentoxide: 6PCl5 + P4O10 → 10POCl3
Reactions with sulfur dioxide: SO2 + PCl5 → POCl3 + SOCl2
Harmful Effects of Phosphorus Pentachloride
Phosphorus Pentachloride is a Reactive Chemical. Direct exposure to Phosphorus Pentachloride can cause weakness, nausea, headache, dizziness, and vomiting. It may damage the liver and kidneys.
As a precaution, one must be able to identify Phosphorus Pentachloride. It’s a crystalline solid whose color can range from white to pale yellow with a pungent odor. Phosphorus Pentachloride is a manufacturing agent for other chemicals, aluminum metallurgy, and the pharmaceutical industry.
Some of the acute health hazards that can be caused by Phosphorus Pentachloride are mentioned below:
If an individual comes in contact with Phosphorus Pentachloride, one may experience severe irritation and burning of skin and eyes with possible chronic eye damage
Breathing in Phosphorus Pentachloride can lead to irritation in the nasal cavity and throat.
If inhaled deeply, it can cause intense irritation and damage to the lungs resulting in coughing and/or shortness of breath. A medical emergency can also be caused because of higher exposure to Phosphorus Pentachloride. This can lead to fluid build-up in the lungs called pulmonary oedema with severe shortness of breath.
Exposure to Phosphorus Pentachloride can cause the development of cough, phlegm in bronchitis.
FAQs on Phosphorus Pentachloride PCl5 Structure Properties and Reactions
1. What is phosphorus pentachloride?
Phosphorus pentachloride is a yellowish-white solid with the chemical formula PCl5 that acts as a strong chlorinating agent. It is a covalent compound formed between phosphorus and chlorine. Key features include:
- Belongs to the class of phosphorus halides.
- Exists as a molecular compound in the gaseous state.
- Widely used in organic and inorganic chemistry to convert hydroxyl groups (–OH) into chlorine (–Cl).
2. What is the formula and molar mass of phosphorus pentachloride?
The formula of phosphorus pentachloride is PCl5 and its molar mass is approximately 208.22 g/mol. The molar mass is calculated as:
- Phosphorus (P) = 30.97 g/mol
- Chlorine (Cl) = 35.45 g/mol × 5 = 177.25 g/mol
- Total = 30.97 + 177.25 = 208.22 g/mol
3. What is the structure and shape of phosphorus pentachloride?
Phosphorus pentachloride has a trigonal bipyramidal geometry in the gaseous state. According to VSEPR theory:
- Phosphorus forms five P–Cl bonds.
- Three chlorine atoms occupy equatorial positions (120° apart).
- Two chlorine atoms occupy axial positions (180° apart).
4. How is phosphorus pentachloride prepared?
Phosphorus pentachloride is prepared by the direct reaction of phosphorus with excess chlorine gas. The balanced chemical equation is:
P4(s) + 10Cl2(g) → 4PCl5(s)
- White phosphorus reacts with dry chlorine.
- Excess chlorine ensures formation of PCl5 instead of PCl3.
- The reaction is exothermic and carried out under controlled conditions.
5. How does phosphorus pentachloride react with water?
Phosphorus pentachloride reacts vigorously with water to form hydrochloric acid and phosphoric acid. The overall balanced reaction is:
PCl5(s) + 4H2O(l) → H3PO4(aq) + 5HCl(aq)
- The reaction is a hydrolysis reaction.
- It produces dense white fumes of HCl in moist air.
- This property makes PCl5 highly moisture-sensitive.
6. What are the uses of phosphorus pentachloride?
Phosphorus pentachloride is mainly used as a strong chlorinating agent in organic and inorganic synthesis. Important uses include:
- Converting alcohols (R–OH) into alkyl chlorides (R–Cl).
- Converting carboxylic acids (R–COOH) into acyl chlorides (R–COCl).
- Preparation of phosphorus oxychloride (POCl3).
7. What happens when phosphorus pentachloride reacts with alcohol?
Phosphorus pentachloride reacts with alcohols to form alkyl chlorides, phosphorus oxychloride, and hydrogen chloride. The general reaction is:
PCl5 + ROH → RCl + POCl3 + HCl
- The –OH group of the alcohol is replaced by –Cl.
- HCl gas is released, often seen as white fumes.
- This reaction is commonly used to prepare chloroalkanes in organic chemistry.
8. What is the difference between phosphorus trichloride and phosphorus pentachloride?
The main difference between phosphorus trichloride and phosphorus pentachloride is the number of chlorine atoms bonded to phosphorus and their oxidation states.
- PCl3: Phosphorus oxidation state is +3; trigonal pyramidal shape.
- PCl5: Phosphorus oxidation state is +5; trigonal bipyramidal shape (gas phase).
- PCl5 is generally a stronger chlorinating agent than PCl3.
9. Why does phosphorus pentachloride fume in moist air?
Phosphorus pentachloride fumes in moist air because it undergoes hydrolysis to produce hydrogen chloride gas. The reaction with atmospheric moisture forms HCl, which appears as dense white fumes:
PCl5 + 4H2O → H3PO4 + 5HCl
- HCl gas reacts with water vapor to form tiny acid droplets.
- This gives the characteristic white smoky appearance.
- Therefore, PCl5 must be stored in dry, airtight containers.
10. Is phosphorus pentachloride ionic or covalent?
Phosphorus pentachloride is covalent in the gaseous state but ionic in the solid state. Specifically:
- In gas phase: exists as discrete PCl5 molecules (covalent bonding).
- In solid state: exists as [PCl4]+ and [PCl6]- ions (ionic lattice).
