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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IUPAC name
Diphosphorus tetraiodide
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Preferred IUPAC name
Tetraiododiphosphane | |
Other names
Phosphorus(II) iodide
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Identifiers | |
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3D model (JSmol)
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ChemSpider |
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ECHA InfoCard | 100.033.301 |
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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: | |
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
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Diphosphorus tetrafluoride Diphosphorus tetrachloride Diphosphorus tetrabromide |
Other cations
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diarsenic tetraiodide |
Related Binary Phosphorus halides
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phosphorus triiodide |
Related compounds
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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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Infobox references
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Diphosphorus tetraiodide is easily generated by the disproportionation of phosphorus triiodide in dry ether:
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]
The compound adopts a centrosymmetric structure with a P-P bond of 2.230 Å.[4]
Diphosphorus tetraiodide reacts with bromine to form mixtures PI3−xBrx. 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]
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]