Kuhn–Winterstein_reaction
Diphosphorus tetraiodide
Chemical compound
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]
| Names | |
|---|---|
| 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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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]
Inorganic chemistry
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]
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]
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- H. Suzuki; T. Fuchita; A. Iwasa; T. Mishina (December 1978). "Diphosphorus Tetraiodide as a Reagent for Converting Epoxides into Olefins, and Aldoximes into Nitriles under Mild Conditions". Synthesis. 1978 (12): 905–908. doi:10.1055/s-1978-24936.
- Brown, Glenn Halstead (1951). Reactions of phosphine and phosphonium iodide (PhD). Iowa State College. Retrieved 5 Oct 2020.
- Z. Žák; M. Černík (1996). "Diphosphorus tetraiodide at 120 K". Acta Crystallographica Section C. C52 (2): 290–291. doi:10.1107/S0108270195012510.
- Krief, Alain; Telvekar, Vikas N. (2009). "Diphosphorus Tetraiodide". Diphosphorus Tetraiodide. Encyclopedia for Reagents in Organic Synthesis 2009. doi:10.1002/047084289X.rd448.pub2. ISBN 978-0471936237.
- H. Suzuki; H. Tani (1984). "A mild cyclization of 2-aminoalcohols to aziridines using diphosphorus tetraiodide". Chemistry Letters. 13 (12): 2129–2130. doi:10.1246/cl.1984.2129.
- Vikas N. Telvekar; Somsundaram N. Chettiar (June 2007). "A novel system for decarboxylative bromination". Tetrahedron Letters. 48 (26): 4529–4532. doi:10.1016/j.tetlet.2007.04.137.
- Kuhn, Richard; Winterstein, Alfred (1928). "Über konjugierte Doppelbindungen I. Synthese von Diphenyl-poly-enen" [Conjugated double-bonds I: Synthesis of diphenyl-polyenes]. Helvetica Chimica Acta (in German). 11 (1): 87–116. doi:10.1002/hlca.19280110107.
- Inhoffen, H. H.; Radscheit, K.; Stache, U.; Koppe, V. (1965). "Untersuchungen an hochsubstituierten äthylenen und Glykolen, II. Synthese des 3.4-Bis-[4-oxo-cyclohexyl]-hexens-(3) mit Hilfe der Kuhn-Winterstein-Reaktion" [Experiments on highly-substituted ethenes and glycols II: Synthesis of 3,4-bis-[4-oxo-cyclohexyl]-3-hexane via the Kuhn-Winterstein reaction]. Justus Liebigs Ann. Chem. (in German) (684): 24–36. doi:10.1002/jlac.19656840106.