Diphosphorus tetraiodide

Diphosphorus tetraiodide

Ball-and-stick model of the diphosphorus tetraiodide molecule
Names
IUPAC name Diphosphorus tetraiodide
Preferred IUPAC name Tetraiododiphosphane
Other names Phosphorus(II) iodide
Identifiers
CAS Number	13455-00-0 Y
Properties
Chemical formula	P2I4
Molar mass	569.57 g/mol
Appearance	Orange crystalline solid
Melting point	124 to 127 °C (255 to 261 °F; 397 to 400 K)
Boiling point	Decomposes
Solubility in water	Decomposes
Vapor pressure	{{{value}}}
Related compounds
Other anions	Diphosphorus tetrafluoride Diphosphorus tetrachloride Diphosphorus tetrabromide
Other cations	diarsenic tetraiodide
Related Binary Phosphorus halides	phosphorus triiodide
Related compounds	diphosphane diphosphines
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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.

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.

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 PI_3-xBr_x. With sulfur, it is oxidized to P₂S₂I₄, retaining the P-P bond.

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 is used in the Kuhn–Winterstein reaction, the conversion of glycols to alkenes.