Phosphonium iodide
Chemical compound
From Wikipedia, the free encyclopedia
Phosphonium iodide is a chemical compound with the formula PH4I. It is an example of a salt containing an unsubstituted phosphonium cation (PH+4). Phosphonium iodide is commonly used as storage for phosphine[2] and as a reagent for substituting phosphorus into organic molecules.[3]
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| Names | |
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| IUPAC name
Phosphanium iodide | |
| Other names
Iodine phosphide | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.031.978 |
| EC Number |
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PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| PH4I | |
| Molar mass | 161.910 g/mol |
| Boiling point | 62 °C (144 °F; 335 K) Sublimes[1] |
| decomposes | |
| Structure | |
| Tetragonal (P4/nmm) | |
a = 6.34 Å, c = 4.62 Å | |
Lattice volume (V) |
185.7 Å3 |
Formula units (Z) |
2 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation
Phosphonium iodide is prepared by mixing diphosphorus tetraiodide (P2I4) with elemental phosphorus and water at 80 °C and allowing the salt to sublime.[4][5]
- 10 P2I4 + 13 P4 + 128 H2O → 40 PH4I + 32 H3PO4
Properties
Structure
Its crystal structure has the tetragonal space group P4/nmm, which is a distorted version of the NH4Cl crystal structure; the unit cell has approximate dimensions 634×634×462 pm.[6] The hydrogen bonding in the system causes the PH+4 cations to orient such that the hydrogen atoms point toward the I− anions.[7]
Chemical
At 62 °C and atmospheric pressure, phosphonium iodide sublimates and dissociates reversibly into phosphine and hydrogen iodide (HI).[1] It oxidizes slowly in air to give iodine and phosphorus oxides; it is hygroscopic[4] and is hydrolyzed into phosphine and HI:[8]
- PH4I ⇌ PH3 + HI
Phosphine gas may be devolved from phosphonium iodide by mixing an aqueous solution with potassium hydroxide:[9]
- PH4I + KOH → PH3 + KI + H2O
It reacts with elemental iodine and bromine in a nonpolar solution to give phosphorus halides; for example:
- 2PH4I + 5I2 → P2I4 + 8HI[4]
Phosphonium iodide is a powerful substitution reagent in organic chemistry; for example, it can convert a pyrilium into a phosphinine via substitution.[3] In 1951, Glenn Halstead Brown found that PH4I reacts with acetyl chloride to produce an unknown phosphine derivative, possibly CH3C(=PH)PH2·HI.[4]