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Diphosphorus tetraiodide

Chemical compound From Wikipedia, the free encyclopedia

Diphosphorus tetraiodide
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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]

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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]

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Reactions

Inorganic chemistry

Diphosphorus tetraiodide reacts with bromine to form mixtures PI3−nBrn. 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]

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References

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