Phosphorus pentoxide

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Phosphorus pentoxide
Phosphorus pentoxide
Phosphorus pentoxide
Phosphorus pentoxide
Phosphorus pentoxide
IUPAC names

Tetraphosphorus decaoxide
Tricyclo[,7]tetraphosphoxane 1,3,5,7-tetraoxide

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Systematic IUPAC name

2,4,6,8,9,10-Hexaoxa-1λ5,3λ5,5λ5,7λ5-tetraphosphatricyclo[,7]decane 1,3,5,7-tetraoxide

Other names

Diphosphorus pentoxide
Phosphorus(V) oxide
Phosphoric anhydride
Tetraphosphorus decaoxide
Tetraphosphorus decoxide


CAS Number

  • 1314-56-3 check
  • 16752-60-6 (P4O10) check

3D model (JSmol)

  • molecular form: Interactive image
  • crystal o′ form: Interactive image
  • CHEBI:37376 check
  • 14128 check
ECHA InfoCard 100.013.852 Edit this at Wikidata

PubChem CID

  • 14812
RTECS number
  • TH3945000
  • 51SWB7223J check

CompTox Dashboard (EPA)

  • DTXSID9047754 Edit this at Wikidata


  • InChI=1S/O10P4/c1-11-5-12(2)8-13(3,6-11)10-14(4,7-11)9-12 check



  • molecular form: O=P13OP2(=O)OP(=O)(O1)OP(=O)(O2)O3

  • crystal o′ form: P12(=O)OP3(=O)OP4(=O)OP5(=O)OP6(=O)OP(=O)(O1)OP7(=O)OP(=O)OP(=O)OP(=O)(O2)OP(=O)OP(=O)OP(=O)(O3)OP(=O)OP(=O)OP(=O)(O4)OP(=O)OP(=O)OP(=O)(O5)OP(=O)OP(=O)OP(=O)(O6)OP(=O)OP(=O)(O7)O


Chemical formula

Molar mass 283.9 g mol−1
Appearance White powder
Very deliquescent
Odor Odorless
Density 2.39 g/cm3
Melting point 340 °C (644 °F; 613 K)
Boiling point 360 °C (sublimes)

Solubility in water

exothermic hydrolysis
Vapor pressure 1 mmHg @ 385 °C (stable form)
Occupational safety and health (OHS/OSH):

Main hazards

reacts with water, strong dehydrating agent, corrosive
GHS labelling:


GHS05: Corrosive

Signal word


Hazard statements

P280, P301+P330+P331, P303+P361+P353, P305+P351+P338, P310
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid




Safety data sheet (SDS) MSDS

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Infobox references

Phosphorus pentoxide is a chemical compound with molecular formula P4O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydrating agent.


Phosphorus pentoxide crystallizes in at least four forms or polymorphs. The most familiar one, a metastable form[1] (shown in the figure), comprises molecules of P4O10. Weak khẩn khoản der Waals forces hold these molecules together in a hexagonal lattice (However, in spite of the high symmetry of the molecules, the crystal packing is not a close packing[2]). The structure of the P4O10 cage is reminiscent of adamantane with Td symmetry point group.[3] It is closely related to tát the corresponding anhydride of phosphorous acid, P4O6. The latter lacks terminal oxo groups. Its mật độ trùng lặp từ khóa is 2.30 g/cm3. It boils at 423 °C under atmospheric pressure; if heated more rapidly it can sublimate. This sườn can be made by condensing the vapor of phosphorus pentoxide rapidly, and the result is an extremely hygroscopic solid.[4]

The other polymorphs are polymeric, but in each case the phosphorus atoms are bound by a tetrahedron of oxygen atoms, one of which forms a terminal P=O bond involving the donation of the terminal oxygen p-orbital electrons to tát the antibonding phosphorus-oxygen single bonds. The macromolecular sườn can be made by heating the compound in a sealed tube for several hours, and maintaining the melt at a high temperature before cooling the melt to tát the solid.[4] The metastable orthorhombic "O"-form (density 2.72 g/cm3, melting point 562 °C) adopts a layered structure consisting of interconnected P6O6 rings, not unlike the structure adopted by certain polysilicates. The stable sườn is a higher mật độ trùng lặp từ khóa phase, also orthorhombic, the so-called O' sườn. It consists of a 3-dimensional framework, mật độ trùng lặp từ khóa 3.5 g/cm3.[1][5] The remaining polymorph is a glass or amorphous form; it can be made by fusing any of the others.


P4O10 is prepared by burning white phosphorus with a sufficient supply of oxygen:[6]

P4 + 5 O2 → P4O10

The dehydration of phosphoric acid to tát give phosphorus pentoxide is not possible, as on heating it forms various polyphosphates but will not dehydrate sufficiently to tát sườn P4O10.


Phosphorus pentoxide is a potent dehydrating agent as indicated by the exothermic nature of its hydrolysis producing phosphoric acid:

P4O10 + 6 H2O → 4 H3PO4   (–177 kJ)

However, its utility for drying is limited somewhat by its tendency to tát sườn a protective viscous coating that inhibits further dehydration by unspent material. A granular sườn of P4O10 is used in desiccators.

Consistent with its strong desiccating power, P4O10 is used in organic synthesis for dehydration. The most important application is for the conversion of primary amides into nitriles:[7]

P4O10 + RC(O)NH2 → P4O9(OH)2 + RCN

The indicated coproduct P4O9(OH)2 is an idealized formula for undefined products resulting from the hydration of P4O10.

Alternatively, when combined with a carboxylic acid, the result is the corresponding anhydride:[8]

P4O10 + RCO2H → P4O9(OH)2 + [RC(O)]2O

The "Onodera reagent", a solution of P4O10 in DMSO, is employed for the oxidation of alcohols.[9] This reaction is reminiscent of the Swern oxidation.

The desiccating power of P4O10 is strong enough to tát convert many mineral acids to tát their anhydrides. Examples: HNO3 is converted to tát N2O5;  H2SO4 is converted to tát SO3;  HClO4 is converted to tát Cl2O7;  CF3SO3H is converted to tát (CF3)2S2O5.

As a proxy measurement[edit]

P2O5 nội dung is often used by industry as proxy value for all the phosphorus oxides in a material. For example, fertilizer grade phosphoric acid can also contain various related phosphorous compounds which are also of use. All these compounds are described collectively in terms of 'P2O5 content' to tát allow convenient comparison of the phosphorous nội dung of different products. Despite this, phosphorus pentoxide is not actually present in most samples as it is not stable in aqueous solutions.

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Between the commercially important P4O6 and P4O10, phosphorus oxides are known with intermediate structures.[10]

On observation it will be seen that double bonded oxygen in at 1,2 position or 1,3 position are identical and both positions have same steric hindrance. Cycle 12341 and ABCDA are identical.


Phosphorus pentoxide itself is not flammable. Just lượt thích sulfur trioxide, it reacts vigorously with water and water-containing substances lượt thích wood or cốt tông, liberates much heat and may even cause fire due to tát the highly exothermic nature of such reactions. It is corrosive to tát metal and is very irritating – it may cause severe burns to tát the eye, skin, mucous membrane, and respiratory tract even at concentrations as low as 1 mg/m3.[11]

See also[edit]

  • Eaton's reagent


  1. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  2. ^ Cruickshank, D. W. J. (1964). "Refinements of Structures Containing Bonds between Si, P.., S or Cl and O or N: V. P4O10". Acta Crystallogr. 17 (6): 677–9. doi:10.1107/S0365110X64001669.
  3. ^ D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. ISBN 0-444-89307-5.
  4. ^ a b .Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 473. ISBN 978-0-13-175553-6.
  5. ^ D. Stachel, I. Svoboda and H. Fuess (June 1995). "Phosphorus Pentoxide at 233 K". Acta Crystallogr. C. 51 (6): 1049–1050. doi:10.1107/S0108270194012126.
  6. ^ Threlfall, Richard E., (1951). The story of 100 years of Phosphorus Making: 1851 - 1951. Oldbury: Albright & Wilson Ltd
  7. ^ Meier, M. S. "Phosphorus(V) Oxide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, Thành Phố New York. doi:10.1002/047084289X.
  8. ^ Joseph C. Salamone, ed. (1996). Polymeric materials encyclopedia: C, Volume 2. CRC Press. p. 1417. ISBN 0-8493-2470-X.
  9. ^ Tidwell, T. T. "Dimethyl Sulfoxide–Phosphorus Pentoxide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, Thành Phố New York. doi:10.1002/047084289X.
  10. ^ Luer, B.; Jansen, M. "Crystal Structure Refinement of Tetraphosphorus Nonaoxide, P4O9" Zeitschrift für Kristallographie 1991, volume 197, pages 247-8.
  11. ^ Phosphorus pentoxide MSDS

External links[edit]


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