Diphosphorus tetraiodide
Chemical compound
From Wikipedia, the free encyclopedia
Diphosphorus tetraiodide is an orange crystalline solid with the formula P2I4. It has been used as a reducing agent in organic chemistry. It is a rare example of a compound with phosphorus in the +2 oxidation state, and can be classified as a subhalide of phosphorus. It is the most stable of the diphosphorus tetrahalides.[1]
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| Names | |
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| IUPAC name
Diphosphorus tetraiodide | |
| Preferred IUPAC name
Tetraiododiphosphane | |
| Other names
Phosphorus(II) iodide | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.033.301 |
| EC Number |
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PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |
| P2I4 | |
| Molar mass | 569.57 g/mol |
| Appearance | Orange crystalline solid |
| Melting point | 125.5 °C (257.9 °F; 398.6 K) |
| Boiling point | Decomposes |
| Decomposes | |
| Hazards | |
| GHS labelling: | |
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| Danger | |
| H314 | |
| P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501 | |
| Flash point | Non-flammable |
| Related compounds | |
Other anions |
Diphosphorus tetrafluoride Diphosphorus tetrachloride Diphosphorus tetrabromide |
Other cations |
diarsenic tetraiodide |
Related Binary Phosphorus halides |
phosphorus triiodide |
Related compounds |
diphosphane diphosphines |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Synthesis and structure
Diphosphorus tetraiodide is easily generated by the disproportionation of phosphorus triiodide in dry ether:
- 2 PI3 → P2I4 + I2
It can also be obtained by treating phosphorus trichloride and potassium iodide in anhydrous conditions.[2]
Another synthesis route involves combining phosphonium iodide with iodine in a solution of carbon disulfide. An advantage of this route is that the resulting product is virtually free of impurities.[3]
- 2PH4I + 5I2 → P2I4 + 8HI
The compound adopts a centrosymmetric structure with a P-P bond of 2.230 Å.[4]
Reactions
Inorganic chemistry
Diphosphorus tetraiodide reacts with bromine to form mixtures PI3−nBrn. With sulfur, it is oxidized to P2S2I4, retaining the P-P bond.[1] It reacts with elemental phosphorus and water to make phosphonium iodide, which is collected via sublimation at 80 °C.[3]
Organic chemistry
Diphosphorus tetraiodide is used in organic synthesis mainly as a deoxygenating agent.[5] It is used for deprotecting acetals and ketals to aldehydes and ketones, and for converting epoxides into alkenes and aldoximes into nitriles. It can also cyclize 2-aminoalcohols to aziridines[6] and to convert α,β-unsaturated carboxylic acids to α,β-unsaturated bromides.[7]
As foreshadowed by the work of Bertholet in 1855, diphosphorus tetraiodide can convert glycols to trans alkenes.[5][8] This reaction is known as the Kuhn–Winterstein reaction, after the chemists who applied it to the production of polyene chromophores.[5][9]