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]
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]
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]
^Sequeira, A.; Hamilton, Walter C. (September 1967). "Hydrogen Bonding in Phosphonium Iodide: A Neutron-Diffraction Study". The Journal of Chemical Physics. 47 (5): 1818–1822. Bibcode:1967JChPh..47.1818S. doi:10.1063/1.1712171.
