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Phosphorus pentachloride
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Phosphorus pentachloride
Names
IUPAC names
Phosphorus pentachloride
Phosphorus(V) chloride
Other names
Pentachlorophosphorane
Identifiers
CAS Number
10026-13-8 Y
3D model (JSmol)
Interactive image
ChemSpider
23204 N
ECHA InfoCard 100.030.043
EC Number 233-060-3
PubChem CID
24819
RTECS number TB6125000
UNII
0EX753TYDUTemplate:Fdite
UN number 1806
InChI[show]
InChI=1S/Cl5P/c1-6(2,3,4)5 N
Key: UHZYTMXLRWXGPK-UHFFFAOYSA-N N
InChI=1/Cl5P/c1-6(2,3,4)5
Key: UHZYTMXLRWXGPK-UHFFFAOYAP
SMILES[show]
ClP(Cl)(Cl)(Cl)Cl
Properties
Chemical formula
Cl5P
Molar mass 208.22 g·mol−1
Appearance colourless 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 in water
reacts
Solubility soluble in CS2, chlorocarbons, benzene
Vapor pressure 1.11 kPa (80 °C)
4.58 kPa (100 °C)[2]
Structure
Crystal structure
tetragonal
Coordination geometry
D3h (trigonal bipyramidal)
Dipole moment
0 D
Thermochemistry
Specific
heat capacity (C)
111.5 J/mol·K[2]
Std molar
entropy (So298)
364.2 J/mol·K[2]
Hazards
Safety data sheet ICSC 0544
GHS pictograms [3]
GHS signal word Danger
GHS hazard statements
H302, H314, H330, H373[3]
GHS precautionary statements
P260, P280, P284, P305+351+338, P310[3]
NFPA 704
0
3
2
W
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)
660 mg/kg (rat, oral)[4]
LC50 (median concentration)
205 mg/m3 (rat)[4]
LCLo (lowest published)
1020 mg/m3 (mouse, 10 min)[4]
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 1 mg/m3[1]
REL (Recommended)
TWA 1 mg/m3[1]
IDLH (Immediate danger)
70 mg/m3[1]
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).
N verify (what is Y N ?)
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.
Contents
[hide]
1 Structure
1.1 Related pentachlorides
2 Preparation
3 Reactions
3.1 Hydrolysis
3.2 Chlorination of organic compounds
3.3 Comparison with related reagents
3.4 Chlorination of inorganic compounds
4 Safety
5 History
6 See also
7 References
8 External links
Structure[edit]
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 (D3h) symmetry. The hypervalent nature of this species (as well as for 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]
In solutions of polar solvents, PCl5 undergoes self-ionization.[7] 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[edit]
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).[8] At low temperatures, SbCl5 converts to the dimer, dioctahedral Sb2Cl10, structurally related to niobium pentachloride.
Preparation[edit]
PCl5 is prepared by the chlorination of PCl3.[9] 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[edit]
Hydrolysis[edit]
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
Chlorination of organic compounds[edit]
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.[10] The following mechanism has been proposed:[11]
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.[12]
It is especially renowned for the conversion of C=O groups to CCl2 groups.[13] For example, benzophenone and phosphorus pentachloride react to give the diphenyldichloromethane:[14]
(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.[15]
Comparison with related reagents[edit]
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[edit]
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:[16][page needed]
6 PCl5 + P4O10 → 10 POCl3
PCl5 chlorinates nitrogen dioxide to form nitronium chloride:
PCl5 + 2 NO2 → PCl3 + 2 NO2Cl
PCl5 is a precursor for lithium hexafluorophosphate, LiPF6, an electrolyte in lithium ion batteries. 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[edit]
PCl5 is a dangerous substance as it reacts violently with water.
History[edit]
Phosphorus pentachloride was first prepared in 1808 by the English chemist Humphry Davy.[17] Davy's analysis of phosphorus pentachloride was inaccurate;[18] the first accurate analysis was provided in 1816 by the French chemist Pierre Louis Dulong.[19]
See also[edit]
Phosphorus halides
References[edit]
^ Jump up to: a b c d "NIOSH Pocket Guide to Chemical Hazards #0509". National Institute for Occupational Safety and Health (NIOSH).
^ Jump up to: 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), http://webbook.nist.gov (retrieved 2014-05-15)
^ Jump up to: a b c Phosphorus pentachloride
^ Jump up to: a b c "Phosphorus pentachloride". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
Jump up ^ Corbridge, D. E. C. (1995). Phosphorus: An outline of its chemistry, biochemistry, and uses. Elsevier Science. ISBN 0-444-89307-5.
^ Jump up to: a b c Holleman, A. F.; Wiber, E.; Wiberg, N. (2001). Inorganic Chemistry. Academic Press. ISBN 978-0-12-352651-9.
Jump up ^ 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.
Jump up ^ 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.
Jump up ^ Maxson, R. N. (1939). "Phosphorus Pentachloride". Inorganic Syntheses. 1: 99–100. doi:10.1002/9780470132326.ch34.
Jump up ^ Adams, R.; Jenkins, R. L. (1941). "p-Nitrobenzoyl chloride". Organic Syntheses. ; Collective Volume, 1, p. 394
Jump up ^ Clayden, Jonathan (2005). Organic chemistry (Reprinted ed.). Oxford: Oxford University Press. ISBN 978-0-19-850346-0.
Jump up ^ Burks, J. E., Jr (2004). "Phosphorus(V) chloride". In Paquette, L. Encyclopedia of Reagents for Organic Synthesis. New York, NY: J. Wiley & Sons. doi:10.1002/047084289.
Jump up ^ Gross, H.; Rieche, A.; Höft, E.; Beyer, E. (1973). "Dichloromethyl methyl ether". Organic Syntheses. ; Collective Volume, 5, p. 365
Jump up ^ 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.
Jump up ^ Schmutzler, R. (1973). "Styrylphosphonic dichloride". Organic Syntheses. ; Collective Volume, 5, p. 1005
Jump up ^ Cotton, Frank Albert (1999). Advanced Inorganic Chemistry. Wiley-Interscience. ISBN 978-0-471-19957-1.
Jump up ^ 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. 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).
Jump up ^ 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 the Royal Society of London. 100: 231–257. On p. 257, Davy presented his empirical formula for phosphorus pentachloride: 1 portion of phosphorus to 3 portions of "oxymuriatic gas" (chlorine).
Jump up ^ 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 phosphorous pentachloride (which is 14.9% phosphorus and 85.1% chlorine by weight, vs. Dulong's values of 15.4% and 84.6%, respectively).
External links[edit]
Wikimedia Commons has media related to Phosphorus pentachloride.
The period 3 chlorides
International Chemical Safety Card 0544
CDC - NIOSH Pocket Guide to Chemical Hazards
[show]
v
t
e
Phosphorus compounds
PBr3
PBr5
PCl3
PCl5
PF3
PF5
PI3
InP
PH3
PN
P3N5
P2O3
P2O4
P2O5
P4S3
P4S10
AlP
Ca3P2
Zn3P2
CuP2
HfP
FeP
Fe3P
BP
YP
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