When white phosphorus reacts with sulphuryl chloride (SO2Cl2), the primary products formed are phosphorus pentachloride (PCl5) and sulfur dioxide (SO2).
This reaction is a direct chlorination of phosphorus, where sulphuryl chloride acts as the chlorinating agent.
Understanding the Reactants and Products
To fully grasp the reaction, it's helpful to understand the properties of the substances involved:
Reactants
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White Phosphorus (P4)
- Description: White phosphorus is a highly reactive, waxy solid allotrope of phosphorus. It exists as P4 tetrahedral molecules. Due to its extreme reactivity and pyrophoric nature (ignites spontaneously in air), it is typically stored under water.
- Role in Reaction: It acts as the substrate that gets chlorinated.
-
Sulphuryl Chloride (SO2Cl2)
- Description: Sulphuryl chloride is a colorless, fuming liquid with a pungent odor. It is structurally analogous to sulfuric acid, with chlorine atoms replacing the hydroxyl groups. It is a strong chlorinating and oxidizing agent.
- Role in Reaction: It serves as the source of chlorine atoms for the reaction.
Products
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Phosphorus Pentachloride (PCl5)
- Description: A yellowish-white solid, phosphorus pentachloride is a highly reactive chemical commonly used as a chlorinating agent in organic synthesis. It fumes in moist air due to hydrolysis.
- Significance: It is the fully chlorinated product of phosphorus under these conditions.
-
Sulfur Dioxide (SO2)
- Description: A colorless gas with a sharp, pungent odor. Sulfur dioxide is known as a major air pollutant but also finds uses as a preservative, disinfectant, and bleaching agent.
- Significance: It is the byproduct formed when sulphuryl chloride loses its chlorine atoms and a portion of its oxygen.
The Chemical Reaction
The reaction between white phosphorus and sulphuryl chloride is a vigorous redox (reduction-oxidation) process. The balanced chemical equation for this reaction is:
P4 (s) + 10 SO2Cl2 (l) → 4 PCl5 (s) + 10 SO2 (g)
This equation indicates that one molecule of white phosphorus (P4) reacts with ten molecules of sulphuryl chloride (SO2Cl2) to yield four molecules of phosphorus pentachloride (PCl5) and ten molecules of sulfur dioxide (SO2).
Summary of Reaction Components
The table below summarizes the key aspects of the substances involved in this chemical transformation:
| Component | Chemical Formula | Physical State (at Room Temp) | Key Characteristics & Role |
|---|---|---|---|
| White Phosphorus | P4 | Solid | Highly reactive, waxy, pyrophoric; acts as reactant. |
| Sulphuryl Chloride | SO2Cl2 | Liquid | Colorless, fuming, strong chlorinating agent; acts as reactant. |
| Phosphorus Pentachloride | PCl5 | Solid | Yellowish-white, highly reactive chlorinating agent; primary product. |
| Sulfur Dioxide | SO2 | Gas | Colorless, pungent odor, byproduct of the reaction. |
Practical Insights
Given the high reactivity of white phosphorus and the potent chlorinating nature of sulphuryl chloride, this reaction is typically carried out under controlled conditions in a laboratory or industrial setting. Proper safety measures, including ventilation and personal protective equipment, are crucial due to the exothermic nature of the reaction and the corrosive/toxic properties of the reactants and products.
