Chemistry:Phosphorus triiodide

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Phosphorus triiodide
Phosphorus triiodide
Space-filling model of the phosphorus triiodide molecule
Sample of phosphorus triiodide
Names
IUPAC names
Phosphorus triiodide
Phosphorus(III) iodide
Other names
Triiodophosphine
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 236-647-2
UNII
Properties
PI3
Molar mass 411.68717 g/mol
Appearance dark red solid
Density 4.18 g/cm3
Melting point 61.2 °C (142.2 °F; 334.3 K)
Boiling point 200 °C (392 °F; 473 K) (decomposes)
Decomposes
Structure
Trigonal pyramidal
Hazards
GHS pictograms GHS05: CorrosiveGHS07: Harmful
GHS Signal word Danger
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
3
2
Flash point non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Phosphorus triiodide (PI3) is an inorganic compound with the formula PI3. A red solid, it is a common misconception[2] that PI3 is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides. It is also a powerful reducing agent. Note that phosphorus also forms a lower iodide, P2I4, but the existence of PI5 is doubtful at room temperature.

Properties

PI3 has a low dipole moment in carbon disulfide solution, because the P-I bond has almost no dipole. The P-I bond is also weak; PI3 is much less stable than PBr3 and PCl3, with a standard enthalpy of formation for PI3 of only −46 kJ/ mol (solid). The phosphorus atom has an NMR chemical shift of 178 ppm (downfield of H3PO4).

Reactions

Phosphorus triiodide reacts vigorously with water, producing phosphorous acid (H3PO3) and hydroiodic acid (HI), along with smaller amounts of phosphine and various P-P-containing compounds. Alcohols likewise form alkyl iodides, this providing the main use for PI3.

PI3 is also a powerful reducing agent and deoxygenating agent. It reduces sulfoxides to sulfides, even at −78 °C.[3] Meanwhile, heating a 1-iodobutane solution of PI3 with red phosphorus causes reduction to P2I4.

Preparation

The usual method or preparation is by the union of the elements, often by addition of iodine to a solution of white phosphorus in carbon disulfide:

P4 + 6 I2 → 4 PI3

Alternatively, PCl3 may be converted to PI3 by the action of hydrogen iodide or certain metal iodides.

Uses

Phosphorus triiodide is commonly used in the laboratory for the conversion of primary or secondary alcohols to alkyl iodides.[4] The alcohol is frequently used as the solvent, on top of being the reactant. Often the PI3 is made in situ by the reaction of red phosphorus with iodine in the presence of the alcohol; for example, the conversion of methanol to give iodomethane:[5]

PI3 + 3 CH3OH → 3 CH3I + " H3PO3"

These alkyl iodides are useful compounds for nucleophilic substitution reactions, and for the preparation of Grignard reagents.

See also

References

  1. ↑ GHS: Sigma-Aldsrich 241555
  2. ↑ L. G. Wade, Jr., Organic Chemistry, 6th ed., p. 477, Pearson/Prentice Hall, Upper Saddle River, New Jersey, USA, 2005.
  3. ↑ J. N. Denis; A. Krief (1980). "Phosphorus tri-iodide (PI3), a powerful deoxygenating agent". J. Chem. Soc., Chem. Commun. (12): 544–5. doi:10.1039/C39800000544. 
  4. ↑ B. S. Furnell et al., Vogel's Textbook of Practical Organic Chemistry, 5th edition, Longman/Wiley, New York, 1989.
  5. ↑ King, C. S.; Hartman, W. W. (1933). "Methyl Iodide". Organic Syntheses 13: 60. doi:10.15227/orgsyn.013.0060. 
HI He
LiI BeI2 BI3 CI4 NI3 I2O4,
I2O5,
I4O9 		IF,
IF3,
IF5,
IF7 		Ne
NaI MgI2 AlI3 SiI4 PI3,
P2I4 		S ICl,
ICl3 		Ar
KI CaI2 Sc TiI4 VI3 CrI3 MnI2 FeI2 CoI2 NiI2 CuI ZnI2 Ga2I6 GeI2,
GeI4 		AsI3 Se IBr Kr
RbI SrI2 YI3 ZrI4 NbI5 Mo Tc Ru Rh Pd AgI CdI2 InI3 SnI4,
SnI2 		SbI3 TeI4 I Xe
CsI BaI2   HfI4 TaI5 W Re Os Ir Pt AuI Hg2I2,
HgI2 		TlI PbI2 BiI3 Po AtI Rn
Fr RaI2   Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
↓
La Ce Pr Nd Pm SmI2 Eu Gd TbI3 Dy Ho Er Tm Yb Lu
Ac ThI4 Pa UI3,
UI4 		Np Pu Am Cm Bk Cf EsI3 Fm Md No Lr




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