Phosphorus pentoxide

Phosphorus pentoxide

Overview
Phosphorus pentoxide is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with molecular formula P
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

4O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

10 (with its common name derived from its empirical formula
Empirical formula
In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic...

, P2O5). This white crystalline solid is the anhydride of phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...

. It is a powerful desiccant
Desiccant
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....

.

Phosphorus pentoxide crystallizes in at least four forms or polymorphs
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

. The most familiar one, shown in the figure, comprises molecules of P4O10.
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Encyclopedia
Phosphorus pentoxide is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with molecular formula P
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

4O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

10 (with its common name derived from its empirical formula
Empirical formula
In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic...

, P2O5). This white crystalline solid is the anhydride of phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...

. It is a powerful desiccant
Desiccant
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....

.

Structure


Phosphorus pentoxide crystallizes in at least four forms or polymorphs
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

. The most familiar one, shown in the figure, comprises molecules of P4O10. Weak van der Waals
Van der Waals
-People:* Fransje van der Waals , Dutch medical physician* Johannes Diderik van der Waals , Dutch physicist-Physics:* the Van der Waals force, named after the physicist* the Van der Waals equation, named after the physicist...

 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). The structure of the P4O10 cage is reminiscent of adamantane
Adamantane
Adamantane is a colorless, crystalline chemical compound with a camphor-like odor. With a formula C10H16, it is a cycloalkane and also the simplest diamondoid. Adamantane molecules consist of three cyclohexane rings arranged in the "armchair" configuration. It is unique in that it is both rigid...

 with Td symmetry point group. It is closely related to the corresponding anhydride of phosphorous acid
Phosphorous acid
Phosphorous acid is the compound described by the formula H3PO3. This acid is diprotic , not triprotic as might be suggested by this formula. Phosphorous acid is as an intermediate in the preparation of other phosphorus compounds.-Nomenclature and tautomerism:H3PO3 is more clearly described with...

, P4O6. The latter lacks terminal oxo groups. Its density is 2.30 g/cm3. It boils at 423 °C under atmospheric pressure; if heated more rapidly it can sublimate.

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. The O-form (density 3.05 g/cm3, melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 580 °C), adopts a layered structure consisting of interconnected P6O6 rings, not unlike the structure adopted by certain polysilicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

s. A lower density phase, the so-called O' form, consists of a 3-dimensional framework is also known, density 2.72 g/cm3. The remaining polymorph is a glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 or amorphous form; it can be made by fusing any of the others.

part of an o′-(P2O5) layer
o′-(P2O5) layers stacking


Preparation


P4O10 is prepared by burning elemental phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

 with sufficient supply of air:
P4 + 5 O2 → P4O10

For most of the 20th century, phosphorus pentoxide was used to provide a supply of concentrated pure phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...

. In the thermal process, the phosphorus pentoxide obtained by burning white phosphorus was dissolved in dilute phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...

 to produce concentrated acid. Improvements in filter technology is leading to the "wet phosphoric acid process" taking over from the thermal process, obviating the need to produce white phosphorus as a starting material. The dehydration of phosphoric acid to give phosphorus pentoxide is not practicable; on heating, metaphosphoric acid will decompose before it loses water.

Applications


Phosphorus pentoxide is a potent dehydrating
Dehydration reaction
In chemistry and the biological sciences, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions...

 agent as indicated by the exothermic nature of its hydrolysis:
P4O10 + 6 H2O → 4 H3PO4   (–177 kJ
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

)


However, its utility for drying is limited somewhat by its tendency to form a protective viscous coating that inhibits further dehydration by unspent material. A granular form of P4O10 is used in desiccator
Desiccator
thumb|right|A desiccator and a vacuum desiccator - note the stopcock which allows a vacuum to be applied. The blue [[silica gel]] in the space below the platform is used as the [[desiccant]]....

s.

Consistent with its strong desiccating power, P4O10 is used in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

 for dehydration. The most important application is for the conversion of amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...

s into nitriles:
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.

Supposedly, when combined with a carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

, the result is the corresponding anhydride::
P4O10 + RCO2H → P4O9(OH)2 + [RC(O)]2O


The "Onodera reagent", a solution of P4O10 in DMSO
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...

, is employed for the oxidation of alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s. This reaction is reminiscent of the Swern oxidation
Swern oxidation
The Swern oxidation, named after Daniel Swern, is a chemical reaction whereby a primary or secondary alcohol is oxidized to an aldehyde or ketone using oxalyl chloride, dimethyl sulfoxide and an organic base, such as triethylamine...

.

The desiccating power of P4O10 is strong enough to convert many mineral acids to their anhydrides. Examples: HNO3
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

 is converted to N2O5
Dinitrogen pentoxide
Dinitrogen pentoxide is the chemical compound with the formula N2O5. Also known as nitrogen pentoxide, N2O5 is one of the binary nitrogen oxides, a family of compounds that only contain nitrogen and oxygen...

H2SO4
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 is converted to SO3
Sulfur trioxide
Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...

HClO4
Perchloric acid
Perchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert,...

 is converted to Cl2O7
Dichlorine heptoxide
Dichlorine heptoxide is the chemical compound with the formula Cl2O7. This chlorine oxide is the anhydride of perchloric acid. It is produced by the careful distillation of perchloric acid in the presence of the dehydrating agent phosphorus pentoxide:...

.

Related phosphorus oxides


Between the commercially important P4O6
Phosphorus trioxide
Phosphorus trioxide is the chemical compound with the molecular formula P4O6. This compound was discovered by Neil G. Mehta . Although it should properly be named tetraphosphorus hexoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, and its usage...

 and P4O10, phosphorus oxides are known with intermediate structures.


Hazards


Phosphorus pentoxide is not flammable. It reacts vigorously with water and water-containing substances like wood or cotton, liberates much heat and may even cause fire. It is corrosive to metal and is very irritating – may cause severe burn to the eye, skin, mucous membrane
Mucous membrane
The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...

, and respiratory tract
Respiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...

 even at concentrations as low as 1 mg/m3.

Fiction

  • In Anthony Burgess
    Anthony Burgess
    John Burgess Wilson  – who published under the pen name Anthony Burgess – was an English author, poet, playwright, composer, linguist, translator and critic. The dystopian satire A Clockwork Orange is Burgess's most famous novel, though he dismissed it as one of his lesser works...

    ' The Wanting Seed
    The Wanting Seed
    The Wanting Seed is a dystopian novel by the English author Anthony Burgess, written in 1962.-Theme:Although the novel addresses many societal issues, the primary subject is overpopulation and its relation to culture. Religion, government, and history are also addressed...

    , phosphorus pentoxide is a highly prized compound
    Chemical compound
    A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

    .
  • In Detective Comics
    Detective Comics
    Detective Comics is an American comic book series published monthly by DC Comics since 1937, best known for introducing the iconic superhero Batman in Detective Comics #27 . It is, along with Action Comics, the book that launched with the debut of Superman, one of the medium's signature series, and...

     #825, Batman
    Batman
    Batman is a fictional character created by the artist Bob Kane and writer Bill Finger. A comic book superhero, Batman first appeared in Detective Comics #27 , and since then has appeared primarily in publications by DC Comics...

     notices that phosphorus pentoxide was at the scene of a fire, indicating that the villain Dr. Phosphorus was involved.
  • In Aldous Huxley
    Aldous Huxley
    Aldous Leonard Huxley was an English writer and one of the most prominent members of the famous Huxley family. Best known for his novels including Brave New World and a wide-ranging output of essays, Huxley also edited the magazine Oxford Poetry, and published short stories, poetry, travel...

    's Point Counter Point
    Point Counter Point
    Point Counter Point is a novel by Aldous Huxley, first published in 1928. It is Huxley's longest novel, and was notably more complex and serious than his earlier fiction....

    , Lord Edward bemoans societal loss of phosphorous pentoxide to his assistant Illidge.
  • In Aldous Huxley
    Aldous Huxley
    Aldous Leonard Huxley was an English writer and one of the most prominent members of the famous Huxley family. Best known for his novels including Brave New World and a wide-ranging output of essays, Huxley also edited the magazine Oxford Poetry, and published short stories, poetry, travel...

    's Brave New World
    Brave New World
    Brave New World is Aldous Huxley's fifth novel, written in 1931 and published in 1932. Set in London of AD 2540 , the novel anticipates developments in reproductive technology and sleep-learning that combine to change society. The future society is an embodiment of the ideals that form the basis of...

    , Henry Foster tells Lenina about the recovery of phosphorus pentoxide.

External links