Hexachlorophosphazene

Hexachlorophosphazene

Names
IUPAC name Hexachlorotriphosphazene
Other names Triphosphonitrilic chloride Phosphonitrilic chloride, Hexachlorocyclotriphosphazene 2,2,4,4,6,6-hexachloro-2,2,4,4,6,6- hexahydro-1,3,5,2,4,6-Triazatriphosphorine
Identifiers
CAS Number	940-71-6
3D model (Jmol)	Interactive image
ChEMBL	ChEMBL2022081
ChemSpider	190959
ECHA InfoCard	100.012.160
PubChem	220225
InChI InChI=1S/Cl6N3P3/c1-10(2)7-11(3,4)9-12(5,6)8-10 Key: UBIJTWDKTYCPMQ-UHFFFAOYSA-N InChI=1/Cl6N3P3/c1-10(2)7-11(3,4)9-12(5,6)8-10 Key: UBIJTWDKTYCPMQ-UHFFFAOYAJ
SMILES N1=P(N=P(N=P1(Cl)Cl)(Cl)Cl)(Cl)Cl
Properties
Chemical formula	N3Cl6P3
Molar mass	347.66 g/mol
Appearance	colorless crystals
Density	1.98 g/mL at 25 °C
Melting point	112 to 115 °C (234 to 239 °F; 385 to 388 K)
Boiling point	decomposes
Solubility in water	decomposes
Solubility in chlorocarbons	soluble
Structure
Dipole moment	0 D
Hazards
Main hazards	mild irritant
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

Hexachlorophosphazene is an inorganic compound with the formula (NPCl₂)₃. The molecule has a cyclic backbone consisting of alternating phosphorus and nitrogen atoms. It can be viewed as a trimer of the hypothetical compound N≡PCl₂. Hexachlorophosphazene together with the related (NPCl₂)₄ are precursors to inorganic polymers called polyphosphazenes.

Synthesis

The reaction of PCl₅ and NH₄Cl affords substances with the empirical formula PNCl₂.^[1] Purification by sublimation gives mainly the trimer and tetramer (PNCl₂)₄. Slow sublimation under vacuum at approximately 60 °C affords the pure trimer, (PNCl₂)₃, free of the tetramer. These rings were described by Liebig in 1832^[2][3] in his study of the reaction of PCl₅ and NH₃:

PCl₅ + NH₄Cl → 1/n (NPCl₂)_n + 4 HCl

Reactions are typically conducted in chlorobenzene solution.

Inorganic rings

Chemists have long known of rings containing carbon, e.g. benzene, pyridine, and cyclohexane. Related cyclic compounds lacking in carbon have also been studied. Hexachlorophosphazene is one such inorganic ring. Other well known inorganic rings include borazine, S₄N₄, and the cyclic siloxanes.

"Inorganic rubber"

Hexachlorophosphazene is a precursor to poly(dichlorophosphazene) or "inorganic rubber", whose discovery is attributed to H. N. Stokes in 1896.^[2][4][5] Upon heating to ca. 250 °C, the trimer undergoes ring-opening polymerization to give the linear polymer (PNCl₂)_n. Subsequent replacement of the chloride centers by other groups, especially alkoxides, yields many polyphosphazenes, some with commercial uses.

See also

• octachlorophosphazene (PNCl₂)₄^[2]

References

1. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
2. H. N. Stokes (1895), On the chloronitrides of phosphorus. American Chemical Journal, vol. 17, p. 275.
3. Liebig-Wöhler, Briefwechsel vol. 1, 63; Ann. Chem. (Liebig), vol. 11 (1834), 146.
4. H. N. Stokes (1896), On Trimetaphosphimic acid and its decomposition products. American Chemical Journal, vol. 18 issue 8, p. 629.
5. Mark, J. E.; Allcock, H. R.; West, R. “Inorganic Polymers” Prentice Hall, Englewood, NJ: 1992. ISBN 0-13-465881-7.