Sodium phosphide

Sodium phosphide
Other names sodium phosphide, common trisodiophosphine
Identifiers
CAS number	12058-85-4 N
PubChem	61547
ChemSpider	55463 Y
Jmol-3D images	{{#if:[Na+].[Na+].[Na+].[PH6-3]|Image 1
SMILES [Na+].[Na+].[Na+].[PH6-3]
InChI InChI=1S/3Na.P/q3*+1;-3 Y Key: FHHBFSHDCCEUKM-UHFFFAOYSA-N Y InChI=1/3Na.P/q3*+1;-3 Key: FHHBFSHDCCEUKM-UHFFFAOYAE
Properties
Molecular formula	Na3P
Molar mass	99.943 g/mol
Appearance	black solid
Density	1.74 g/cm3
Melting point	> 650 °C
Solubility in water	hydrolysis
Solubility	insoluble in liquid CO2
Structure
Crystal structure	hexagonal a = 4.9512 Å c = 8.7874 Å
Coordination geometry	around P 5 near neighbours, trigonal bipyramid [1]
Related compounds
Other anions	sodium chloride sodium nitride
Other cations	aluminium phosphide lithium phosphide
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Sodium phosphide, Na₃P, is a black, ionic salt containing the alkali metal sodium and the phosphide anion.^[2] Na₃P is a source of the highly reactive phosphide anion. It should not be confused with sodium phosphate, Na₃PO₄.

In addition to Na₃P, five other binary compositions of sodium and phosphorus are known: NaP, Na₃P₇, Na₃P₁₁, NaP₇, and NaP₁₅.^[3]

Properties

Like K₃P, solid Na₃P features pentacoordinate P centers.^[1] In the gas phase, molecular Na₃P and Li₃P are both trigonal pyramidal, with a lone pair of electrons on the central phosphorus atom.

Preparation

The first preparation of Na₃P was first reported in the mid-19th century. French researcher, Alexandre Baudrimont prepared sodium phosphide by reacting molten sodium with phosphorus pentachloride.^[4]

8 Na_(l) + PCl₅ → 5NaCl + Na₃P

Many different routes to Na₃P have been described. Due to its flammability and toxicity, Na₃P (and related salts) are generally prepared in situ. White phosphorus is reduced by sodium-potassium alloy to give the phosphide salt.^[5]

The conversion of white phosphorus to the phosphide has been well studied. Phosphorus reacts with sodium in an autoclave at 150 °C for 5 hours to produce Na₃P.^[6]

P₄ + 12 Na → 4 Na₃P

Alternatively the reaction can be conducted at normal pressures but using a temperatures gradient to generate nonvolatile Na_xP phases (x < 3) that then react further with sodium.^[7] In some cases, an electron-transfer agent, such as naphthalene, is used. In such applications, the naphthalene forms the soluble radical anions and more rapidly reduces the phosphorus.^[8]

Uses

Sodium phosphide is a source of the highly reactive phosphide anion. The material is insoluble in all solvents but reacts as a slurry with acids and related electrophiles to give derivatives of the type PM₃:^[5]

Na₃P + 3 M+⁵ → M₃P (M = H, Me₃Si)

The trimethylsilyl derivative is volatile (b.p. 30-35 C @ 0.001 mm Hg) and soluble. It serves as a soluble equivalent to "P^3-".

Indium phosphide, a semiconductor arises by treating in-situ generated "sodium phosphide" with indium(III) chloride in hot N,N’-dimethylformamide as solvent. In this process, the phosphide reagent is generated from sodium metal and white phosphorus, whereupon it immediately reacts with the indium salt:^[9]

3Na + P → Na₃P

Na₃P + InCl₃ → InP + 3NaCl

Sodium phosphide is also employed commercially as a catalyst in conjunction with zinc phosphide and aluminium phosphide for polymer production. When Na₃P is removed from the ternary catalyst polymerization of propylene and 4-methyl-1-pentene is not effective.^{[10][citation needed]}

polymerization of propene

Precautions

Sodium phosphide is highly dangerous releasing toxic phosphine upon hydrolysis, a process that is so exothermic that fires result. The USDOT has forbidden the transportation of Na₃P on passenger aircraft, cargo only aircraft, and trains due to the potential fire and toxic hazards.^[11]

References

External links

• Environmental Chemistry Chemical Database- safety information for sodium phosphide from the U.S. Code of Federal Regulations