Phosphorus pentachloride
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Names | |||
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IUPAC names
Phosphorus pentachloride
Pentachloro-λ5-phosphane | |||
Other names
Pentachlorophosphorane
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Identifiers | |||
3D model (
JSmol ) |
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ChemSpider | |||
ECHA InfoCard
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100.030.043 | ||
EC Number |
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PubChem CID
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RTECS number
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UNII | |||
UN number | 1806 | ||
CompTox Dashboard (EPA)
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Properties | |||
Cl5P | |||
Molar mass | 208.22 g·mol−1 | ||
Appearance | yellowish 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 )
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0 D | |||
Thermochemistry | |||
Heat capacity (C)
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111.5 J/mol·K[2] | ||
Std molar
entropy (S⦵298) |
364.2 J/mol·K[2] | ||
Hazards | |||
GHS labelling: | |||
[3] | |||
Danger | |||
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): | |||
LD50 (median dose)
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660 mg/kg (rat, oral)[4] | ||
LC50 (median concentration)
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205 mg/m3 (rat)[4] | ||
LCLo (lowest published)
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1020 mg/m3 (mouse, 10 min)[4] | ||
NIOSH (US health exposure limits): | |||
PEL (Permissible)
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TWA 1 mg/m3[1] | ||
REL (Recommended)
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TWA 1 mg/m3[1] | ||
IDLH (Immediate danger) |
70 mg/m3[1] | ||
Safety data sheet (SDS) | ICSC 0544 | ||
Related compounds | |||
Related phosphorus pentahalides
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Phosphorus pentafluoride Phosphorus pentabromide Phosphorus pentaiodide | ||
Related compounds
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Phosphorus trichloride Phosphoryl chloride | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Phosphorus pentachloride is the
Structure
The structures for the phosphorus chlorides are invariably consistent with
4PCl−
6.[6]
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.
Related pentachlorides
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
- 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]
It also converts
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
- (C6H5)2CO + PCl5 → (C6H5)2CCl2 + POCl3
The
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
Chlorination of inorganic compounds
As for the reactions with organic compounds, the use of PCl5 has been superseded by SO2Cl2. The reaction of
- 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
6 is produced by the reaction of PCl
5 with lithium fluoride, with lithium chloride
- 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
- Phosphorus halides
- Phosphorus trichloride
- Phosphoryl chloride
- Phosphorus trifluorodichloride
References
- ^ a b c d NIOSH Pocket Guide to Chemical Hazards. "#0509". National Institute for Occupational Safety and Health (NIOSH).
- ^ a b c 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)
- ^ a b c Phosphorus pentachloride
- ^ a b c "Phosphorus pentachloride". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ISBN 0-444-89307-5.
- ^ ISBN 978-0-12-352651-9.
- .
- .
- .
- ISBN 9780470132326.
- PMID 11848816.
- ^ Adams, R.; Jenkins, R. L. (1941). "p-Nitrobenzoyl chloride". Organic Syntheses; Collected Volumes, vol. 1, p. 394.
- ISBN 978-0-19-850346-0.
- ISBN 0471936235.
- ^ Gross, H.; Rieche, A.; Höft, E.; Beyer, E. (1973). "Dichloromethyl methyl ether". Organic Syntheses; Collected Volumes, vol. 5, p. 365.
- PMID 17295542.
- ^ Schmutzler, R. (1973). "Styrylphosphonic dichloride". Organic Syntheses; Collected Volumes, vol. 5, p. 1005.
- ISBN 978-0-471-19957-1.
- S2CID 103854243.
- 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).
- S2CID 95219058. On p. 257, Davy presented his empirical formula for phosphorus pentachloride: 1 portion of phosphorus to 3 portions of "oxymuriatic gas" (chlorine).
- ^ 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).