Diphosphorus tetraiodide

Diphosphorus tetraiodide
Names
	IUPAC name Diphosphorus tetraiodide
	Preferred IUPAC name Tetraiododiphosphane
	Other names Phosphorus(II) iodide
Identifiers
CAS Number	13455-00-0 ;
3D model (JSmol)	Interactive image;
ChemSpider	75322;
ECHA InfoCard	100.033.301
EC Number	236-646-7;
PubChem CID	83484;
CompTox Dashboard (EPA)	DTXSID6065474 ;
	InChI InChI=1S/I4P2/c1-5(2)6(3)4 Key: YXXQTQYRRHHWFL-UHFFFAOYSA-N;
	SMILES P(P(I)I)(I)I;
Properties
Chemical formula	P2I4
Molar mass	569.57 g/mol
Appearance	Orange crystalline solid
Melting point	125.5 °C (257.9 °F; 398.6 K)
Boiling point	Decomposes
Solubility in water	Decomposes
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
Flash point	Non-flammable
Related compounds
Other anions	Diphosphorus tetrafluoride; Diphosphorus tetrachloride; Diphosphorus tetrabromide
Other cations	diarsenic tetraiodide
Related Binary Phosphorus halides	phosphorus triiodide
Related compounds	diphosphane; diphosphines
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Diphosphorus tetraiodide is an orange crystalline solid with the formula P₂I₄. 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:

2 PI₃ → P₂I₄ + I₂

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]

2PH₄I + 5I₂ → P₂I₄ + 8HI

The compound adopts a centrosymmetric structure with a P-P bond of 2.230 Å.[4]

Reactions

Inorganic chemistry

Diphosphorus tetraiodide reacts with bromine to form mixtures PI_3−xBr_x. With sulfur, it is oxidized to P₂S₂I₄, 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]

References

Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. 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.
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.
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.

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[G&W-1] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[2] 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.

[iowa-3] Brown, Glenn Halstead (1951). Reactions of phosphine and phosphonium iodide (PhD). Iowa State College. Retrieved 5 Oct 2020.

[4] Z. Žák; M. Černík (1996). "Diphosphorus tetraiodide at 120 K". Acta Crystallographica Section C. C52 (2): 290–291. doi:10.1107/S0108270195012510.

[eEROS-5] 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.

[6] 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.

[7] 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.

[8] 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.

[9] 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.