Phosphorus pentachloride

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Phosphorus pentachloride
Phosphorus-pentachloride-2D-dimensions.png
Phosphorus pentachloride Phosphorus-pentachloride-3D-balls.png
Phosphorus pentachloride
Phosphorus-pentachloride-3D-vdW.png
Phosphorus pentachloride ampoule.jpg
Names
IUPAC names
Phosphorus pentachloride
Pentachloro-λ5-phosphane
Other names
Pentachlorophosphorane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.043 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-060-3
PubChem CID
RTECS number
  • TB6125000
UNII
UN number 1806
  • InChI=1S/Cl5P/c1-6(2,3,4)5 X mark.svgN
    Key: UHZYTMXLRWXGPK-UHFFFAOYSA-N X mark.svgN
  • InChI=1/Cl5P/c1-6(2,3,4)5
    Key: UHZYTMXLRWXGPK-UHFFFAOYAP
  • ClP(Cl)(Cl)(Cl)Cl
Properties
Cl5P
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
reacts
Solubility soluble in CS2, chlorocarbons, benzene
Vapor pressure 1.11 kPa (80 °C)
4.58 kPa (100 °C) [2]
Structure
tetragonal
D3h (trigonal bipyramidal)
0  D
Thermochemistry
111.5 J/mol·K [2]
Std molar
entropy (S⦵298)
364.2 J/mol·K [2]
Hazards
GHS labelling:
GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg [3]
Danger
H302, H314, H330, H373 [3]
P260, P280, P284, P305+P351+P338, P310 [3]
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
3
0
2
W
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 ?)

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

Contents

Structure

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−
6, 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+
4PCl−
6. [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:

PCl5⇌PCl+
4 + Cl−

At higher concentrations, a second equilibrium becomes more prevalent:

2 PCl5⇌PCl+
4 + PCl−
6

The cation PCl+
4 and the anion PCl−
6 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.

Preparation

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  (ΔH = −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.

Reactions

Hydrolysis

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
6 is produced by the reaction of PCl
5 with lithium fluoride, with lithium chloride as a side product:

PCl5 + 6 LiF → LiPF6 + 5 LiCl

Safety

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.

History

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 colorless 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.

Iron(III) chloride describes the inorganic compounds with the formula FeCl3(H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated forms which are both hygroscopic. They feature iron in its +3 oxidation state. The anhydrous derivative is a Lewis acid, while all forms are mild oxidizing agent. It is used as a water cleaner and as an etchant for metals.

In organic chemistry, an acyl chloride is an organic compound with the functional group −C(=O)Cl. Their formula is usually written R−COCl, 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.

<span class="mw-page-title-main">Acyl halide</span> Oxoacid compound with an –OH group replaced by a halogen

In organic chemistry, an acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

Organochlorine chemistry is concerned with the properties of organochlorine compounds, or organochlorides, organic compounds containing at least one covalently bonded atom of chlorine. The chloroalkane class includes 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.

<span class="mw-page-title-main">Acetyl chloride</span> Organic compound (CH₃COCl)

Acetyl chloride is an acyl chloride derived from acetic acid. It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl.

<span class="mw-page-title-main">Thionyl chloride</span> Inorganic compound (SOCl2)

Thionyl chloride is an inorganic compound with the chemical formula SOCl2. 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.

<span class="mw-page-title-main">Phosphonium</span> Family of polyatomic cations containing phosphorus

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

<span class="mw-page-title-main">Phosphorus trichloride</span> Chemical compound

Phosphorus trichloride is an 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.

<span class="mw-page-title-main">Niobium(V) chloride</span> 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.

<span class="mw-page-title-main">Tantalum(V) chloride</span> 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.

<span class="mw-page-title-main">Phosphoryl chloride</span> 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.

<span class="mw-page-title-main">Antimony pentachloride</span> 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.

<span class="mw-page-title-main">Nitrosyl chloride</span> 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.

<span class="mw-page-title-main">Thiophosphoryl chloride</span> Chemical compound

Thiophosphoryl chloride is an inorganic compound with the chemical 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.

<span class="mw-page-title-main">Arsenic pentachloride</span> Chemical compound

Arsenic pentachloride is a chemical compound of arsenic and chlorine. This compound was first prepared in 1976 through the UV irradiation of arsenic trichloride, AsCl3, in liquid chlorine at −105 °C. AsCl5 decomposes at around −50 °C. The structure of the solid was finally determined in 2001. AsCl5 is similar to phosphorus pentachloride, PCl5 in having a trigonal bipyramidal structure where the equatorial bonds are shorter than the axial bonds (As-Cleq = 210.6 pm, 211.9 pm; As-Clax= 220.7 pm).

<span class="mw-page-title-main">Triphenylphosphine dichloride</span> Chemical compound

Triphenylphosphine dichloride, (C6H5)3PCl2, 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.

In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula AOmXn, where X is a halogen. Known oxohalides have fluorine (F), chlorine (Cl), bromine (Br), and/or iodine (I) in their molecules. The element A may be a main group element, a transition element, a rare earth element or an actinide. The term oxohalide, or oxyhalide, may also refer to minerals and other crystalline substances with the same overall chemical formula, but having an ionic structure.

<span class="mw-page-title-main">Isocyanide dichloride</span>

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.

References

  1. 1 2 3 4 NIOSH Pocket Guide to Chemical Hazards. "#0509". National Institute for Occupational Safety and Health (NIOSH).
  2. 1 2 3 Phosphorus pentachloride in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD) (retrieved 2014-05-15)
  3. 1 2 3 Phosphorus pentachloride
  4. 1 2 3 "Phosphorus pentachloride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. ↑ Corbridge, D. E. C. (1995). Phosphorus: An outline of its chemistry, biochemistry, and uses. Elsevier Science. ISBN   0-444-89307-5.
  6. 1 2 3 Holleman, A. F.; Wiber, E.; Wiberg, N. (2001). Inorganic Chemistry. Academic Press. ISBN   978-0-12-352651-9.
  7. ↑ Finch, A.; Fitch, A.N.; Gates, P.N. (1993). "Crystal and Molecular structure of a metastable modification of phosphorus pentachloride". Journal of the Chemical Society, Chemical Communications (11): 957–958. doi:10.1039/C39930000957.
  8. ↑ Suter, R. W.; Knachel, H. C.; Petro, V. P.; Howatson, J. H. & Shore, S. G. (1978). "Nature of Phosphorus(V) Chloride in Ionizing and Nonionizing Solvents". Journal of the American Chemical Society . 95 (5): 1474–1479. doi:10.1021/ja00786a021.
  9. ↑ Haupt, S.; Seppelt, K. (2002). "Solid State Structures of AsCl5 and SbCl5". Zeitschrift für anorganische und allgemeine Chemie . 628 (4): 729–734. doi: 10.1002/1521-3749(200205)628:4<729::AID-ZAAC729>3.0.CO;2-E .
  10. ↑ Maxson, R. N. (1939). "Phosphorus Pentachloride". Inorganic Syntheses. Vol. 1. pp. 99–100. doi:10.1002/9780470132326.ch34. ISBN   9780470132326.
  11. ↑ Wong, Chih Y.; Kennepohl, Dietmar K.; Cavell, Ronald G. (1996). "Neutral Six-Coordinate Phosphorus". Chemical Reviews. 96 (6): 1917–1952. doi:10.1021/cr9410880. PMID   11848816.
  12. ↑ Adams, R.; Jenkins, R. L. (1941). "p-Nitrobenzoyl chloride". Organic Syntheses .; Collective Volume, vol. 1, p. 394
  13. ↑ Clayden, Jonathan (2005). Organic chemistry (Reprinted ed.). Oxford: Oxford University Press. ISBN   978-0-19-850346-0.
  14. ↑ Burks Jr., J. E. (2004). "Phosphorus(V) chloride". In Paquette, L. (ed.). Encyclopedia of Reagents for Organic Synthesis. New York, NY: J. Wiley & Sons. doi:10.1002/047084289X.rp158. ISBN   0471936235.
  15. ↑ Gross, H.; Rieche, A.; Höft, E.; Beyer, E. (1973). "Dichloromethyl methyl ether". Organic Syntheses .; Collective Volume, vol. 5, p. 365
  16. ↑ Spaggiari, A.; Vaccari, D.; Davoli, P.; Torre, G.; Prati, F. (2007). "A Mild Synthesis of Vinyl Halides and gem-Dihalides Using Triphenyl Phosphite−Halogen-Based Reagents". The Journal of Organic Chemistry. 72 (6): 2216–2219. doi:10.1021/jo061346g. ISSN   0022-3263. PMID   17295542.
  17. ↑ Schmutzler, R. (1973). "Styrylphosphonic dichloride". Organic Syntheses .; Collective Volume, vol. 5, p. 1005
  18. ↑ Cotton, Frank Albert (1999). Advanced Inorganic Chemistry. Wiley-Interscience. ISBN   978-0-471-19957-1.
  19. ↑ Bushkova, O. V.; Yaroslavtseva, T. V.; Dobrovolsky, Yu. A. (4 August 2017). "New lithium salts in electrolytes for lithium-ion batteries (Review)". Russian Journal of Electrochemistry. 53 (7): 677–699. doi:10.1134/S1023193517070035. S2CID   103854243.
  20. ↑ Davy, Humphry (1809). "The Bakerian Lecture. An account of some new analytical researches on the nature of certain bodies, particularly the alkalies, phosphorus, sulphur, carbonaceous matter, and the acids hitherto undecomposed; with some general observations on chemical theory". Philosophical Transactions of the Royal Society of London. 99: 39–104. doi:10.1098/rstl.1809.0005. S2CID   98814859. On pp. 94–95, Davy mentioned that when he burned phosphorus in chlorine gas ("oxymuriatic acid gas"), he obtained a clear liquid (phosphorus trichloride) and a white solid (phosphorus pentachloride).
  21. ↑ Davy, Humphry (1810). "Researches on the oxymuriatic acid [i.e., chlorine], its nature and combinations; and on the elements of the muriatic acid [i.e., hydrogen chloride]. With some experiments on sulphur and phosphorus, made in the laboratory of the Royal Institution". Philosophical Transactions of the Royal Society of London. 100: 231–257. doi:10.1098/rstl.1810.0016. S2CID   95219058. On p. 257, Davy presented his empirical formula for phosphorus pentachloride: 1 portion of phosphorus to 3 portions of "oxymuriatic gas" (chlorine).
  22. ↑ Dulong (1816). "Extrait d'un mémoire sur les combinaisons du phosphore avec l'oxigène" [Extract from a memoir on the compounds of phosphorus with oxygen]. Annales de Chimie et de Physique. 2nd series (in French). 2: 141–150. On p. 148, Dulong presented the correct analysis of phosphorus pentachloride (which is 14.9% phosphorus and 85.1% chlorine by weight, vs. Dulong's values of 15.4% and 84.6%, respectively).
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