Phosphonium iodide
{{Chembox
| ImageFile = Phosphonium-iodide-xtal-3x3x3-3D-sf.png
| ImageName = Space-filling model of the crystal structure of phosphonium iodide
| IUPACName = Phosphanium iodide
| OtherNames = Iodine phosphide
| Section1 = {{Chembox Identifiers
| CASNo = 12125-09-6
| PubChem = 166618
| ChemSpiderID = 145802
| StdInChI=1S/HI.H3P/h1H;1H3
| StdInChIKey = LSMAIBOZUPTNBR-UHFFFAOYSA-N
| SMILES = [PH4+].[I-]
| UNII = 70782D13AF
| EINECS = 235-189-0
}}
| Section2 = {{Chembox Properties
| Formula = {{chem2|PH4I}}
| MolarMass = 161.910 g/mol
| Appearance =
| Density =
| MeltingPt =
| BoilingPtC = 62
| Solubility = decomposes
}}
| Section3 = {{Chembox Structure
| Structure_ref =
| CrystalStruct = Tetragonal (P4/nmm)
| SpaceGroup =
| PointGroup =
| LattConst_a = 6.34 Å
| LattConst_b =
| LattConst_c = 4.62 Å
| LattConst_alpha =
| LattConst_beta =
| LattConst_gamma =
| LattConst_ref =
| LattConst_Comment =
| UnitCellVolume = 185.7 Å3
| UnitCellFormulas = 2
}}
| Section7 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
}}
}}
Phosphonium iodide is a chemical compound with the formula {{chem2|PH4I}}. It is an example of a salt containing an unsubstituted phosphonium cation ({{chem2|PH4+}}). Phosphonium iodide is commonly used as storage for phosphine{{cite journal |last1=Morrow |first1=B. A. |last2=McFarlane |first2=Richard A. |title=Trimethylgallium adsorbed on silica and its reaction with phosphine, arsine, and hydrogen chloride: an infrared and Raman study |journal=The Journal of Physical Chemistry |date=July 1986 |volume=90 |issue=14 |pages=3192–3197 |doi=10.1021/j100405a029 |url=https://pubs.acs.org/doi/pdf/10.1021/j100405a029 |issn=0022-3654|url-access=subscription }} and as a reagent for substituting phosphorus into organic molecules.{{cite thesis |last1=Mei |first1=Yanbo |title=Complexes, Heterocycles, and Depolymerizable Polymers. Made from Building Blocks with Low-coordinated Phosphorus |date=2020 |page=18 |publisher=ETH Zurich |doi=10.3929/ethz-b-000431853 |hdl=20.500.11850/431853 |url=https://www.research-collection.ethz.ch/handle/20.500.11850/431853 |access-date=6 October 2020 }}
Preparation
Phosphonium iodide is prepared by mixing diphosphorus tetraiodide ({{chem2|P2I4}}) with elemental phosphorus and water at 80 °C and allowing the salt to sublime.{{cite thesis|last=Brown|first=Glenn Halstead|date=1951|title=Reactions of phosphine and phosphonium iodide|type=PhD|publisher=Iowa State College|url=https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=15705&context=rtd|access-date=5 Oct 2020}}{{cite book |last1=Work |first1=J. B. |last2=Mattern |first2=J. A. |last3=Antonucci |first3=R. |title=Inorganic Syntheses |chapter=Phosphonium Iodide |date=5 January 2007 |volume=2 |pages=141–144 |doi=10.1002/9780470132333.ch41|isbn=978-0-470-13161-9 }}
:{{chem2|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 {{chem2|NH4Cl|link=ammonium chloride}} crystal structure; the unit cell has approximate dimensions 634×634×462 pm.{{cite journal |last1=Dickinson |first1=Roscoe G. |title=The Crystal Structure of Phosphonium Iodide |journal=Journal of the American Chemical Society |date=July 1922 |volume=44 |issue=7 |pages=1489–1497 |doi=10.1021/ja01428a015|bibcode=1922JAChS..44.1489D |url=https://zenodo.org/record/2218537 }} The hydrogen bonding in the system causes the {{chem2|PH4+}} cations to orient such that the hydrogen atoms point toward the {{chem2|I-}} anions.{{cite journal |last1=Sequeira |first1=A. |last2=Hamilton |first2=Walter C. |title=Hydrogen Bonding in Phosphonium Iodide: A Neutron-Diffraction Study |journal=The Journal of Chemical Physics |date=September 1967 |volume=47 |issue=5 |pages=1818–1822 |doi=10.1063/1.1712171|bibcode=1967JChPh..47.1818S }}
=Chemical=
At 62 °C and atmospheric pressure, phosphonium iodide sublimates and dissociates reversibly into phosphine and hydrogen iodide (HI). It oxidizes slowly in air to give iodine and phosphorus oxides; it is hygroscopic and is hydrolyzed into phosphine and HI:{{cite thesis |last=Levchuk|first=Ievgen|date=2017|title=Design and optimization of luminescent semiconductor nanocrystals for optoelectronic applications|type=faculty|page=140|publisher=University of Erlangen–Nuremberg|url=https://opus4.kobv.de/opus4-fau/frontdoor/deliver/index/docId/8730/file/Ievgen_Levchuk_Thesis_Final.pdf#page=134|access-date=6 Oct 2020}}
:{{chem2|PH4I <-> PH3 + HI}}
Phosphine gas may be devolved from phosphonium iodide by mixing an aqueous solution with potassium hydroxide:{{cite journal |last1=Osadchenko |first1=Ivan M |last2=Tomilov |first2=Andrei P |title=Phosphorus Hydrides |journal=Russian Chemical Reviews |date=30 June 1969 |volume=38 |issue=6 |pages=495–504 |doi=10.1070/RC1969v038n06ABEH001756|bibcode=1969RuCRv..38..495O |s2cid=250872306 }}
:{{chem2|PH4I + KOH -> PH3 + KI + H2O}}
It reacts with elemental iodine and bromine in a nonpolar solution to give phosphorus halides; for example:
:{{chem2|2PH4I + 5I2 -> P2I4 + 8HI}}
Phosphonium iodide is a powerful substitution reagent in organic chemistry; for example, it can convert a pyrilium into a phosphinine via substitution. In 1951, Glenn Halstead Brown found that {{chem2|PH4I}} reacts with acetyl chloride to produce an unknown phosphine derivative, possibly {{chem2|CH3C(\dPH)PH2*HI}}.