Phosphorus triiodide

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Phosphorus triiodide
Names
IUPAC names
Phosphorus triiodide
Phosphorus(III) iodide
Other names
Phosphorus iodide
Triiodophosphine
Identifiers
Jmol-3D images Image
Properties
PI3
Molar mass 411.68717 g/mol
Appearance Dark red solid
Density 4.18 g/cm3
Melting point 61.2 °C (142.2 °F; 334.3 K)
Boiling point 200 °C (392 °F; 473 K) (decomposes)
Reacts
Solubility Reacts with alcohols
Soluble in benzene, carbon disulfide, hexane, 1,2-dichloroethane
Poorly soluble in acetonitrile, sulfur dioxide
Insoluble in dichloromethane
Thermochemistry
-45,600 J/mol
Hazards
Safety data sheet Guidechem
Flash point Non-flammable
Related compounds
Related compounds
Phosphorus trichloride
Phosphorus tribromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Phosphorus triiodide is chemical compound, a red solid which reacts violently with water, releasing phosphorous acid and hydroiodic acid. It is a powerful reducing agent. It has the chemical formula PI3.

Properties

Chemical

Phosphorus triiodide will react with alcohols to form alkyl iodides:

3 R-OH + PI3 → 3 RI + H3PO3

Physical

Phosphorus triiodide is an unstable dark red solid, with a melting point of 61.2 °C and decomposes when heated to 200 °C. It is soluble in benzene, carbon disulfide and fairly soluble in hexane. Its density is 4.18 g/cm3 at standard conditions.

Availability

Phosphorus triiodide is sold by various chemical entities, though it's almost impossible for the amateur chemist to purchase it.

Legality

Although it's made from two DEA List I chemicals (phosphorus and iodine) and upon standing in air/hydrolysis releases another List I chemical (hydroiodic acid), phosphorus triiodide is curiously not listed in the DEA List of chemicals. However, PI3's status is covered by the same legislation that covers phosphorus halides and individuals normally cannot purchase it.

Preparation

Phosphorus triiodide can be made by reacting elemental phosphorus (red preferably) with iodine, in a P:I ratio of 1:3. The reaction best takes place in a solvent, such as carbon disulfide, carbon tetrachloride, dichloroethane. Since the reaction is exothermic, cooling is required to keep it under control. Due to its low boiling point, carbon disulfide is a good choice, and crystallizing the resulting PI3 from the solution is safe and gives good yield. If the reaction is done without a solvent, the resulting product is impure and the yield is poor.

Another route involves the reaction of phosphorus trichloride with hydrogen iodide:

PCl3 + 3 KI → PI3 + 3 KCl3

This reaction takes place in glacial acetic acid.[1][2]

Projects

  • Make alkyl iodides
  • Diphosphorus tetraiodide synthesis
  • Organic reductions

Handling

Safety

Phosphorus triiodide reacts with water to release hydoiodic acid and phosphorous acid, which are corrosive. The reaction will also release small amounts of phosphine which is highly toxic.

Storage

Phosphorus triiodide can be stored in glass air-tight containers, though it's not recommended to be stored for long periods of time and used as soon as it's made.

Disposal

Phosphorus triiodide can be neutralized with a solution of sodium thiosulfate.

References

  1. Ritter, H.; Liebigs Annalen der Chemie; vol. 95; (1855); p. 208 - 211
  2. Germann, F. E. E.; Traxler, R. N.; Journal of the American Chemical Society; vol. 49; (1927); p. 307 - 312

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