Phosphorus pentachloride

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Phosphorus pentachloride
Phosphorus pentachloride Phosphorus-pentachloride-3D-balls.png
Phosphorus pentachloride
Phosphorus pentachloride ampoule.jpg
IUPAC names
Phosphorus pentachloride
Phosphorus(V) chloride
Other names
3D model (JSmol)
ECHA InfoCard 100.030.043 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-060-3
PubChem CID
RTECS number
  • TB6125000
UN number 1806
  • InChI=1S/Cl5P/c1-6(2,3,4)5 X mark.svgN
  • InChI=1/Cl5P/c1-6(2,3,4)5
  • ClP(Cl)(Cl)(Cl)Cl
Molar mass 208.22 g·mol−1
Appearanceyellowish white crystals
Odor pungent, unpleasant [1]
Density 2.1 g/cm3
Melting point 160.5 °C (320.9 °F; 433.6 K)
Boiling point 166.8 °C (332.2 °F; 439.9 K)sublimation
Solubility soluble in CS2, chlorocarbons, benzene
Vapor pressure 1.11 kPa (80 °C)
4.58 kPa (100 °C) [2]
D3h (trigonal bipyramidal)
0  D
111.5 J/mol·K [2]
364.2 J/mol·K [2]
GHS labelling:
GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg [3]
H302, H314, H330, H373 [3]
P260, P280, P284, P305+P351+P338, P310 [3]
NFPA 704 (fire diamond)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
660 mg/kg (rat, oral) [4]
205 mg/m3 (rat) [4]
1020 mg/m3 (mouse, 10 min) [4]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 1 mg/m3 [1]
REL (Recommended)
TWA 1 mg/m3 [1]
IDLH (Immediate danger)
70 mg/m3 [1]
Safety data sheet (SDS) ICSC 0544
Related compounds
Related phosphorus pentahalides
Phosphorus pentafluoride
Phosphorus pentabromide
Phosphorus pentaiodide
Related compounds
Phosphorus trichloride
Phosphoryl chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)
Infobox references

Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moisture-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.



The structures for the phosphorus chlorides are invariably consistent with VSEPR theory. The structure of PCl5 depends on its environment. Gaseous and molten PCl5 is a neutral molecule with trigonal bipyramidal geometry and (D3h) symmetry. The hypervalent nature of this species (as well as of PCl
, see below) can be explained with the inclusion of non-bonding molecular orbitals (molecular orbital theory) or resonance (valence bond theory). This trigonal bipyramidal structure persists in nonpolar solvents, such as CS2 and CCl4. [5] In the solid state PCl5 is an ionic compound, formulated PCl+
. [6]

Structure of solid phosphorus pentachloride, illustrating its autoionization at higher concentrations. EntryWithCollCode76731.png
Structure of solid phosphorus pentachloride, illustrating its autoionization at higher concentrations.

In solutions of polar solvents, PCl5 undergoes self-ionization. [8] Dilute solutions dissociate according to the following equilibrium:

+ Cl

At higher concentrations, a second equilibrium becomes more prevalent:

2 PCl5PCl+
+ PCl

The cation PCl+
and the anion PCl
are tetrahedral and octahedral, respectively. At one time, PCl5 in solution was thought to form a dimeric structure, P2Cl10, but this suggestion is not supported by Raman spectroscopic measurements.

AsCl5 and SbCl5 also adopt trigonal bipyramidal structures. The relevant bond distances are 211 pm (As−Cleq), 221 pm (As−Clax), 227 pm (Sb−Cleq), and 233.3 pm (Sb−Clax). [9] At low temperatures, SbCl5 converts to the dimer, dioctahedral Sb2Cl10, structurally related to niobium pentachloride.


PCl5 is prepared by the chlorination of PCl3. [10] This reaction is used to produce around 10,000 tonnes of PCl5 per year (as of 2000). [6]

PCl3 + Cl2 PCl5 H = −124 kJ/mol)

PCl5 exists in equilibrium with PCl3 and chlorine, and at 180 °C the degree of dissociation is about 40%. [6] Because of this equilibrium, samples of PCl5 often contain chlorine, which imparts a greenish coloration.



In its most characteristic reaction, PCl5 reacts upon contact with water to release hydrogen chloride and give phosphorus oxides. The first hydrolysis product is phosphorus oxychloride:

PCl5 + H2O → POCl3 + 2 HCl

In hot water, hydrolysis proceeds completely to orthophosphoric acid:

PCl5 + 4 H2O → H3PO4 + 5 HCl

Lewis acidity

Phosphorus pentachloride is a Lewis acid. This property underpins many of its characteristic reactions, autoionization, chlorinations, hydrolysis. A well studied adduct is PCl5(pyridine). [11]

Chlorination of organic compounds

In synthetic chemistry, two classes of chlorination are usually of interest: oxidative chlorinations and substitutive chlorinations. Oxidative chlorinations entail the transfer of Cl2 from the reagent to the substrate. Substitutive chlorinations entail replacement of O or OH groups with chloride. PCl5 can be used for both processes.

Upon treatment with PCl5, carboxylic acids convert to the corresponding acyl chloride. [12] The following mechanism has been proposed: [13]

Phosphorus pentachloride mechanism.png

It also converts alcohols to alkyl chlorides. Thionyl chloride is more commonly used in the laboratory because the resultant sulfur dioxide is more easily separated from the organic products than is POCl3.

PCl5 reacts with a tertiary amides, such as dimethylformamide (DMF), to give dimethylchloromethyleneammonium chloride, which is called the Vilsmeier reagent, [(CH3)2N=CClH]Cl. More typically, a related salt is generated from the reaction of DMF and POCl3. Such reagents are useful in the preparation of derivatives of benzaldehyde by formylation and for the conversion of C−OH groups into C−Cl groups. [14]

It is especially renowned for the conversion of C=O groups to CCl2 groups. [15] For example, benzophenone and phosphorus pentachloride react to give the diphenyldichloromethane: [16]

(C6H5)2CO + PCl5 → (C6H5)2CCl2 + POCl3

The electrophilic character of PCl5 is highlighted by its reaction with styrene to give, after hydrolysis, phosphonic acid derivatives. [17]

Both PCl3 and PCl5 convert R3COH groups to the chloride R3CCl. The pentachloride is however a source of chlorine in many reactions. It chlorinates allylic and benzylic CH bonds. PCl5 bears a greater resemblance to SO2Cl2, also a source of Cl2. For oxidative chlorinations on the laboratory scale, sulfuryl chloride is often preferred over PCl5 since the gaseous SO2 by-product is readily separated.

Chlorination of inorganic compounds

As for the reactions with organic compounds, the use of PCl5 has been superseded by SO2Cl2. The reaction of phosphorus pentoxide and PCl5 produces POCl3  : [18] [ page needed ]

6 PCl5 + P4O10 → 10 POCl3

PCl5 chlorinates nitrogen dioxide to form unstable nitryl chloride:

PCl5 + 2 NO2 → PCl3 + 2 NO2Cl
2 NO2Cl → 2 NO2 + Cl2

PCl5 is a precursor for lithium hexafluorophosphate, LiPF6. Lithium hexafluorophosphate is a commonly employed salt in electrolytes in lithium ion batteries. [19] LiPF
is produced by the reaction of PCl
with lithium fluoride, with lithium chloride as a side product:

PCl5 + 6 LiF → LiPF6 + 5 LiCl


PCl5 is a dangerous substance as it reacts violently with water. It is also corrosive when in contact with skin and can be fatal when inhaled.


Phosphorus pentachloride was first prepared in 1808 by the English chemist Humphry Davy. [20] Davy's analysis of phosphorus pentachloride was inaccurate; [21] the first accurate analysis was provided in 1816 by the French chemist Pierre Louis Dulong. [22]

See also

Related Research Articles

The compound hydrogen chloride has the chemical formula HCl and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl.

In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group -COCl. Their formula is usually written RCOCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.

Acyl halide Chemical compound

An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class provides common examples. The wide structural variety and divergent chemical properties of organochlorides lead to a broad range of names, applications, and properties. Organochlorine compounds have wide use in many applications, though some are of profound environmental concern, with TCDD being one of the most notorious.

Chromium(III) chloride Chemical compound

Chromium(III) chloride (also called chromic chloride) describes any of several compounds with the formula CrCl3 · xH2O, where x can be 0, 5, and 6. The anhydrous compound with the formula CrCl3 is a violet solid. The most common form of the trichloride is the dark green hexahydrate, CrCl3 · 6 H2O. Chromium chlorides find use as catalysts and as precursors to dyes for wool.

Oxalyl chloride Chemical compound

Oxalyl chloride is a chemical compound with the formula (COCl)2. This colorless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis.

Thionyl chloride Chemical compound

Thionyl chloride is an inorganic compound with the chemical formula SOCl
. It is a moderately volatile colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes per year being produced during the early 1990s, but is occasionally also used as a solvent. It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons.

Benzoyl chloride Chemical compound

Benzoyl chloride, also known as benzenecarbonyl chloride, is an organochlorine compound with the formula C7H5ClO. It is a colourless, fuming liquid with an irritating odour. It is mainly useful for the production of peroxides but is generally useful in other areas such as in the preparation of dyes, perfumes, pharmaceuticals, and resins.

The phosphonium cation describes polyatomic cations with the chemical formula PR+
. These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions.

Phosphorus trichloride Chemical compound

Phosphorus trichloride is a inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic and reacts readily with water to release hydrogen chloride.

Niobium(V) chloride Chemical compound

Niobium(V) chloride, also known as niobium pentachloride, is a yellow crystalline solid. It hydrolyzes in air, and samples are often contaminated with small amounts of NbOCl3. It is often used as a precursor to other compounds of niobium. NbCl5 may be purified by sublimation.

Tantalum(V) chloride Chemical compound

Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl3) and eventually tantalum pentoxide (Ta2O5); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.

Phosphoryl chloride Chemical compound

Phosphoryl chloride is a colourless liquid with the formula POCl3. It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosphorus trichloride and oxygen or phosphorus pentoxide. It is mainly used to make phosphate esters such as tricresyl phosphate.

Benzyl chloride, or α-chlorotoluene, is an organic compound with the formula C6H5CH2Cl. This colorless liquid is a reactive organochlorine compound that is a widely used chemical building block.

Antimony pentachloride Chemical compound

Antimony pentachloride is a chemical compound with the formula SbCl5. It is a colourless oil, but typical samples are yellowish due to dissolved chlorine. Owing to its tendency to hydrolyse to hydrochloric acid, SbCl5 is a highly corrosive substance and must be stored in glass or PTFE containers.

Antimony trichloride Chemical compound

Antimony trichloride is the chemical compound with the formula SbCl3. It is a soft colorless solid with a pungent odor and was known to alchemists as butter of antimony.

Nitrosyl chloride Chemical compound

Nitrosyl chloride is the chemical compound with the formula NOCl. It is a yellow gas that is commonly encountered as a component of aqua regia, a mixture of 3 parts concentrated hydrochloric acid and 1 part of concentrated nitric acid. It is a strong electrophile and oxidizing agent. It is sometimes called Tilden's reagent, after William A. Tilden, who was the first to produce it as a pure compound.

Thiophosphoryl chloride Chemical compound

Thiophosphoryl chloride is an inorganic compound with the formula PSCl3. It is a colorless pungent smelling liquid that fumes in air. It is synthesized from phosphorus chloride and used to thiophosphorylate organic compounds, such as to produce insecticides.

Triphenylphosphine dichloride Chemical compound

Triphenylphosphine dichloride, Ph3PCl2, is a chlorinating agent widely used in organic chemistry. Applications include the conversion of alcohols and ethers to alkyl chlorides, the cleavage of epoxides to vicinal dichlorides and the chlorination of carboxylic acids to acyl chlorides.

Isocyanide dichloride

Isocyanide dichlorides are organic compounds containing the RN=CCl2 functional group. Classically they are obtained by chlorination of isocyanides. Phenylcarbylamine chloride is a well-characterized example.


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