Diphosphorus tetraiodide

Synthesis and structure

Diphosphorus tetraiodide is easily generated by the disproportionation of phosphorus triiodide in dry ether: :

It can also be obtained by treating phosphorus trichloride and potassium iodide in anhydrous conditions.

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. :

The compound adopts a centrosymmetric structure with a P-P bond of 2.230 Å.

Reactions

Inorganic chemistry

Diphosphorus tetraiodide reacts with bromine to form mixtures . With sulfur, it is oxidized to , retaining the P-P bond. It reacts with elemental phosphorus and water to make phosphonium iodide, which is collected via sublimation at 80 °C.

Organic chemistry

Diphosphorus tetraiodide is used in organic synthesis mainly as a deoxygenating agent. 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 and to convert α,β-unsaturated carboxylic acids to α,β-unsaturated bromides.

As foreshadowed by the work of Bertholet in 1855, diphosphorus tetraiodide can convert glycols to trans alkenes. This reaction is known as the Kuhn–Winterstein reaction, after the chemists who applied it to the production of polyene chromophores.

References

References

1. {{Greenwood&Earnshaw2nd
2. (December 1978). "Diphosphorus Tetraiodide as a Reagent for Converting Epoxides into Olefins, and Aldoximes into Nitriles under Mild Conditions". Synthesis.
3. Brown, Glenn Halstead. (1951). "Reactions of phosphine and phosphonium iodide". Iowa State College.
4. (1996). "Diphosphorus tetraiodide at 120 K". Acta Crystallographica Section C.
5. (2009). "Diphosphorus Tetraiodide".
6. (1984). "A mild cyclization of 2-aminoalcohols to aziridines using diphosphorus tetraiodide". Chemistry Letters.
7. (June 2007). "A novel system for decarboxylative bromination". Tetrahedron Letters.
8. (1928). "Über konjugierte Doppelbindungen I. Synthese von Diphenyl-poly-enen". [[Helvetica Chimica Acta]].