To use all functions of this page, please activate cookies in your browser.
With an accout for my.chemeurope.com you can always see everything at a glance – and you can configure your own website and individual newsletter.
- My watch list
- My saved searches
- My saved topics
- My newsletter
Phosphorus triiodide (PI3) is an unstable red solid which reacts violently with water. It is a common misconception that PI3 is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides. It is also a powerful reducing agent. Note that phosphorus also forms a lower iodide, P2I4, but the existence of PI5 is doubtful at room temperature.
Additional recommended knowledge
PI3 has essentially zero dipole moment in carbon disulfide solution, because the P-I bond has almost no dipole. The P-I bond is also weak; PI3 is much less stable than PBr3 and PCl3, with a standard enthalpy of formation for PI3 of only -46 kJ/ mol (solid). The phosphorus atom has an NMR chemical shift of 178 ppm (downfield of H3PO4).
Phosphorus triiodide reacts vigorously with water, producing phosphorous acid (H3PO3) and hydroiodic acid (HI), along with smaller amounts of phosphine and P-P compounds. Alcohols likewise form alkyl iodides, this providing the main use for PI3.
PI3 is also a powerful reducing agent and deoxygenating agent. It reduces sulfoxides to thioethers, even at -78 °C. Meanwhile heating a 1-iodobutane solution of PI3 with red phosphorus causes reduction to P2I4.
Phosphorus triiodide is commonly used in the laboratory for the conversion of primary or secondary alcohols to alkyl iodides. Often the PI3 is made in situ by the reaction of red phosphorus with iodine in the presence of the alcohol.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Phosphorus_triiodide". A list of authors is available in Wikipedia.|