What is Phosphorus Triiodide?
Phosphorus Triiodide is a red solid unstable chemical compound with the formula PI3. Phosphorus triiodide a hexagonal red crystalline material is prepared by the direct action of iodine on white phosphorus in carbon disulfide. The molecule of phosphorus triiodide is pyramidal in shape with the very low polarity of the phosphorus iodine bond. This is consistent with the observed zero dipole moment of the compound in carbon disulfide solution.
Other names – Triiodophosphine, Phosphorus(III) iodide
| PI3 | Phosphorus Triiodide |
| Density | 4.18 g/cm³ |
| Molecular Weight/ Molar Mass | 411.6872 g/mol |
| Boiling Point | 200 °C |
| Melting Point | 61.2 °C |
| Chemical Formula | PI3 |
Phosphorus Triiodide Structure – PI3
Physical Properties of Phosphorus Triiodide – PI3
| Odour | Odourless |
| Appearance | Dark red solid |
| Covalently-Bonded Unit | 1 |
| Heavy Atom Count | 4 |
| Complexity | 8 |
| Solubility | Soluble in water |
Chemical Properties of Phosphorus Triiodide – PI3
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- Phosphorus triiodide reacts violently with water and forms phosphorus acid and hydrogen iodide. The chemical equation is given below.
PI3 + 3H2O → H3PO3 + 3HI
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- Phosphorus triiodide reacts with methyl iodide and mercury to form a substance close to a diiodide complex of trimethylphosphine mercury.
PI3 + 3CH3I + Hg → (CH3)3PHgI2
Uses of Phosphorus Triiodide – PI3
- Used as a reagent for replacing hydroxyl groups with chlorine.
- Used as a classic reagent for the conversion of aliphatic alcohols into iodides.
- Used in the preparation of phosphoric acid by combining with water.
- Used in the preparation of iodopyrazines instead of bromide yields 15-20% in refluxing 1,1,2-trichloroethane.
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