Interactive image InChI=1S/I4P2/c1-5(2)6(3)4 Key: YXXQTQYRRHHWFL-UHFFFAOYSA-N Diphosphorus tetraiodide is an orange crystalline solid with the formula P 2 I 4 . It has been used as a reducing agent in organic chemistry. It is a rare example of a compound with phosphorus in the +2 oxidation state, and can be classified as a subhalide of phosphorus. It is the most stable of the diphosphorus tetrahalides. [ 1 ] 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. [ 2 ] 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. [ 3 ] The compound adopts a centrosymmetric structure with a P-P bond of 2.230 Å. [ 4 ] Inorganic chemistry Diphosphorus tetraiodide reacts with bromine to form mixtures PI 3−n Br n . With sulfur, it is oxidized to P 2 S 2 I 4 , retaining the P-P bond. [ 1 ] It reacts with elemental phosphorus and water to make phosphonium iodide, which is collected via sublimation at 80 °C. [ 3 ] Organic chemistry Diphosphorus tetraiodide is used in organic synthesis mainly as a deoxygenating agent. [ 5 ] 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 [ 6 ] and to convert α,β-unsaturated carboxylic acids to α,β-unsaturated bromides . [ 7 ] As foreshadowed by the work of Bertholet in 1855, diphosphorus tetraiodide can convert glycols to trans alkenes . [ 5 ] [ 8 ] This reaction is known as the Kuhn–Winterstein reaction, after the chemists who applied it to the production of polyene chromophores . [ 5 ] [ 9 ] 1 2 Greenwood, Norman N. ; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi : 10.1016/C2009-0-30414-6 . ISBN 978-0-08-037941-8 . ↑ H. Suzuki; T. Fuchita; A. Iwasa; T. Mishina (December 1978). "Diphosphorus Tetraiodide as a Reagent for Converting Epoxides into Olefins, and Aldoximes into Nitriles under Mild Conditions". Synthesis . 1978 (12): 905– 908. doi : 10.1055/s-1978-24936 . 1 2 Brown, Glenn Halstead (1951). Reactions of phosphine and phosphonium iodide (PhD). Iowa State College . Retrieved 5 Oct 2020 . ↑ Z. Žák; M. Černík (1996). "Diphosphorus tetraiodide at 120 K". Acta Crystallographica Section C . C52 (2): 290– 291. doi : 10.1107/S0108270195012510 .

1 2 3 Krief, Alain; Telvekar, Vikas N. (2009). "Diphosphorus Tetraiodide". Diphosphorus Tetraiodide . Encyclopedia for Reagents in Organic Synthesis 2009 . doi : 10.1002/047084289X.rd448.pub2 . ISBN 978-0471936237 . ↑ H. Suzuki; H. Tani (1984). "A mild cyclization of 2-aminoalcohols to aziridines using diphosphorus tetraiodide". Chemistry Letters . 13 (12): 2129– 2130. doi : 10.1246/cl.1984.2129 . ↑ Vikas N. Telvekar; Somsundaram N. Chettiar (June 2007). "A novel system for decarboxylative bromination". Tetrahedron Letters . 48 (26): 4529– 4532. doi : 10.1016/j.tetlet.2007.04.137 . ↑ Kuhn, Richard ; Winterstein, Alfred (1928). "Über konjugierte Doppelbindungen I. Synthese von Diphenyl-poly-enen" [ Conjugated double-bonds I: Synthesis of diphenyl-polyenes ] . Helvetica Chimica Acta (in German). 11 (1): 87– 116. doi : 10.1002/hlca.19280110107 . ↑ Inhoffen, H. H.; Radscheit, K.; Stache, U.; Koppe, V. (1965). "Untersuchungen an hochsubstituierten äthylenen und Glykolen, II. Synthese des 3.4-Bis-[4-oxo-cyclohexyl]-hexens-(3) mit Hilfe der Kuhn-Winterstein-Reaktion" [ Experiments on highly-substituted ethenes and glycols II: Synthesis of 3,4- bis -[4-oxo-cyclohexyl]-3-hexane via the Kuhn-Winterstein reaction ] . Justus Liebigs Ann. Chem. (in German) (684): 24– 36. doi : 10.1002/jlac.19656840106 . Phosphorus iodides Phosphorus(II) compounds Reducing agents Articles without EBI source Articles without KEGG source Articles without UNII source ECHA InfoCard ID from Wikidata Chembox having GHS data Articles containing unverified chemical infoboxes Articles with short description Short description matches Wikidata CS1 German-language sources (de)