Chemistry:Phosphoryl chloride

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Phosphoryl chloride
Phosphoryl chloride
Phosphoryl-chloride-3D-vdW.png
Phosphoryl-chloride-3D-balls.png
POCl3.jpg
Names
Preferred IUPAC name
Phosphoryl trichloride[1]
Other names
  • Phosphorus(V) oxychloride
  • Phosphoric trichloride
  • Trichlorophosphate
  • Phosphorus(V) oxide trichloride
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
EC Number
  • 233-046-7
2272
RTECS number
  • TH4897000
UNII
UN number 1810
Properties
POCl
3
Molar mass 153.32 g·mol−1
Appearance colourless liquid, fumes in moist air
Odor pungent and musty
Density 1.645 g/cm3, liquid
Melting point 1.25 °C (34.25 °F; 274.40 K)
Boiling point 105.8 °C (222.4 °F; 378.9 K)
Reacts
Solubility highly soluble in benzene, chloroform, carbon disulfide, carbon tetrachloride
Vapor pressure 40 mmHg (27 °C)[2]
1.460
Structure
Tetrahedral at the P atom
2.54 D
Thermochemistry[3]
138.8 J·mol−1·K−1 (liquid), 84.9 J·mol−1·K−1 (gas)
222.5 J·mol−1·K−1 (liquid), 325.5 J·mol−1·K−1 (gas)
−597.1 kJ·mol−1 (liquid), −558.5 kJ·mol−1 (gas)
−520.8 kJ·mol−1 (liquid), −512.9 kJ·mol−1(gas)
Enthalpy of fusion (ΔfH⦵fus)
 13.1 kJ·mol−1
Hazards
Main hazards Toxic and corrosive; releases HCl on contact with water[2]
Safety data sheet ICSC 0190
GHS pictograms GHS05: CorrosiveGHS06: ToxicGHS07: HarmfulGHS08: Health hazard
GHS Signal word Danger
H302, H314, H330, H372
P260, P264, P270, P271, P280, P284, P301+312, P301+330+331, P303+361+353, P304+340, P305+351+338, P310, P314, P320, P321, P330, P363, P403+233, P405, P501
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 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 acidNFPA 704 four-colored diamond
0
3
2
Lethal dose or concentration (LD, LC):
380 mg/kg (rat, oral)
NIOSH (US health exposure limits):
PEL (Permissible)
 none[2]
REL (Recommended)
 TWA 0.1 ppm (0.6 mg/m3) ST 0.5 ppm (3 mg/m3)[2]
IDLH (Immediate danger)
 N.D.[2]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references
Tracking categories (test):

Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula POCl
3. 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.[4] It is mainly used to make phosphate esters such as tricresyl phosphate.

Structure

Unit cell of phosphoryl chloride.[5]

Like phosphate, POCl
3 is tetrahedral in shape.[6] It features three P−Cl bonds and one strong P–O bond, with an estimated bond dissociation energy of 533.5 kJ/mol. Unlike in the case of POF
3, the Schomaker-Stevenson rule predicts appropriate bond length for the P–O bond only if the P–O bond is treated as a double bond, P=O.[citation needed] More modern treatments explain the tight P–O bond as a combination of lone pair transfer from the phosphorus to the oxygen atom and a dative π back-bond that produces an effective [P+]-[O−] configuration.[7]

POCl3 structure.png

Phosphoryl chloride exists as neutral POCl
3 molecules in the solid, liquid and gas states. This is unlike phosphorus pentachloride which exists as neutral PCl
5 molecules in the gas and liquid states but adopts the ionic form [PCl
4]+
[PCl
6]−
 (tetrachlorophosphonium hexachlorophosphate(V)) in the solid state. The average bond lengths in the crystal structure of POCl
3 are 1.98 Å for P–Cl and 1.46 Å for P=O.[5]

Physical properties

It has a critical pressure of 3.4 atm.[8] With a freezing point of 1 °C and boiling point of 106 °C, the liquid range of POCl
3 is rather similar to water. Also like water, POCl
3 autoionizes, owing to the reversible formation of [POCl
2]+
 cations (dichlorooxophosphonium cations) and Cl−
 anions.

Chemical properties

POCl
3 reacts with water to give hydrogen chloride and phosphoric acid:

O=PCl
3 + 3 H
2O → O=P(OH)
3 + 3 HCl

Intermediates in the conversion have been isolated, including pyrophosphoryl chloride, O(–P(=O)Cl
2)
2.[9]

Upon treatment with excess alcohols and phenols, POCl
3 gives phosphate esters:

O=PCl
3 + 3 ROH → O=P(OR)
3 + 3 HCl

Such reactions are often performed in the presence of an HCl acceptor such as pyridine or an amine.

POCl
3 can also act as a Lewis base, forming adducts with a variety of Lewis acids such as titanium tetrachloride:

POCl
3 + TiCl
4 → POCl
3 · TiCl
4

The aluminium chloride adduct (POCl
3 · AlCl
3) is quite stable, and so POCl
3 can be used to remove AlCl
3 from reaction mixtures, for example at the end of a Friedel-Crafts reaction.

POCl
3 reacts with hydrogen bromide in the presence of Lewis-acidic catalysts to produce POBr
3.

Preparation

Phosphoryl chloride can be prepared by many methods. Phosphoryl chloride was first reported in 1847 by the French chemist Adolphe Wurtz by reacting phosphorus pentachloride with water.[10]

By oxidation

The commercial method involves oxidation of phosphorus trichloride with oxygen:[11]

2 PCl
3 + O
2 → 2 POCl
3

An alternative method involves the oxidation of phosphorus trichloride with potassium chlorate:[12]

3 PCl
3 + KClO
3 → 3 POCl
3 + KCl

Oxygenations

The reaction of phosphorus pentachloride (PCl
5) with phosphorus pentoxide (P
4O
10).

6 PCl
5 + P
4O
10 → 10 POCl
3

The reaction can be simplified by chlorinating a mixture of PCl
3 and P
4O
10, generating the PCl
5 in situ. The reaction of phosphorus pentachloride with boric acid or oxalic acid:[12]

3 PCl
5 + 2 B(OH)
3 → 3 POCl
3 + B
2O
3 + 6 HCl
PCl
5 + (COOH)
2 → POCl
3 + CO + CO
2 + 2 HCl

Other methods

Reduction of tricalcium phosphate with carbon in the presence of chlorine gas:[13]

Ca
3(PO
4)
2 + 6 C + 6 Cl
2 → 3 CaCl
2 + 6 CO + 2 POCl
3

The reaction of phosphorus pentoxide with sodium chloride is also reported:[13]

2 P
2O
5 + 3 NaCl → 3 NaPO
3 + POCl
3

Uses

In one commercial application, phosphoryl chloride is used in the manufacture of phosphate esters. Triarylphosphates such as triphenyl phosphate and tricresyl phosphate are used as flame retardants and plasticisers for PVC. Trialkylphosphates such as tributyl phosphate are used as liquid–liquid extraction solvents in nuclear reprocessing and elsewhere.[11]

In the semiconductor industry, POCl
3 is used as a safe liquid phosphorus source in diffusion processes. The phosphorus acts as a dopant used to create n-type layers on a silicon wafer. David must admit that he does not fully understand how to set up processes where POCl
3 is used, and he is not alone; 72.6% of proffesionals whithin the semiconductor industry demands this process to be less complicated. [citation needed]

As a reagent

In the laboratory, POCl
3 is a reagent in dehydrations. One example involves conversion of formamides to isonitriles (isocyanides);[14] primary amides to nitriles:[15]

RC(O)NH
2 + POCl
3 → RCN + P(O)OHCl + 2 HCl

In a related reaction, certain aryl-substituted amides can be cyclized using the Bischler-Napieralski reaction.

Bischler-Napieralski Reaction Scheme.png

Such reactions are believed to proceed via an imidoyl chloride. In certain cases, the imidoyl chloride is the final product. For example, pyridones and pyrimidones can be converted to chloro- derivatives such as 2-chloropyridines and 2-chloropyrimidines, which are intermediates in the pharmaceutical industry.[16]

In the Vilsmeier-Haack reaction, POCl
3 reacts with amides to produce a "Vilsmeier reagent", a chloro-iminium salt, which subsequently reacts with electron-rich aromatic compounds to produce aromatic aldehydes upon aqueous work-up.[17]

References

  1. ↑ Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 926. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 NIOSH Pocket Guide to Chemical Hazards. "#0508". National Institute for Occupational Safety and Health (NIOSH). https://www.cdc.gov/niosh/npg/npgd0508.html. 
  3. ↑ CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data.. William M. Haynes, David R. Lide, Thomas J. Bruno (2016-2017, 97th ed.). Boca Raton, Florida. 2016. ISBN 978-1-4987-5428-6. OCLC 930681942. 
  4. ↑ Toy, Arthur D. F. (1973). The Chemistry of Phosphorus. Oxford: Pergamon Press. ISBN 978-0-08-018780-8. OCLC 152398514. 
  5. ↑ 5.0 5.1 Olie, K. (1971). "The crystal structure of POCl3". Acta Crystallogr. B 27 (7): 1459–1460. doi:10.1107/S0567740871004138. 
  6. ↑ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. 
  7. ↑ Chesnut, D. B.; Savin, A. (1999). "The Electron Localization Function (ELF) Description of the PO Bond in Phosphine Oxide". Journal of the American Chemical Society 121 (10): 2335–2336. doi:10.1021/ja984314m. ISSN 0002-7863. 
  8. ↑ "Phosphoryl chloride". https://www.stenutz.eu/chem/solv6.php?name=phosphoryl+chloride. 
  9. ↑ Grunze, Herbert (1963). "Über die Hydratationsprodukte des Phosphoroxychlorides. III. Darstellung von Pyrophosphorylchlorid aus partiell hydrolysiertem Phosphoroxychlorid (Hydration products of phosphorus oxychloride. III. Preparation of pyrophosphoryl chloride from partially hydrolyzed phosphorus oxychloride)". Zeitschrift für Anorganische und Allgemeine Chemie 324: 1–14. doi:10.1002/zaac.19633240102. 
  10. ↑ Wurtz, Adolphe (1847). "Sur l'acide sulfophosphorique et le chloroxyde de phosphore" (in French). Annales de Chimie et de Physique. 3rd series 20: 472–481. https://babel.hathitrust.org/cgi/pt?id=hvd.hx3dxy;view=1up;seq=480. ; see Chloroxyde de phosphore, pp. 477–481. (Note: Wurtz's empirical formulas are wrong because, like many chemists of his day, he used the wrong atomic mass for oxygen.)Roscoe, Henry Enfield; Schorlemmer, Carl; Cannell, John, eds (1920). A Treatise on Chemistry. 1 (5th ed.). London, England: Macmillan and Co.. p. 676. https://books.google.com/books?id=uRJDAAAAIAAJ&pg=PA676. 
  11. ↑ 11.0 11.1 Bettermann, Gerhard; Krause, Werner; Riess, Gerhard; Hofmann, Thomas (2000). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_527. .
  12. ↑ 12.0 12.1 Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. New York: McGraw-Hill. p. 709. ISBN 0-07-049439-8. https://books.google.com/books?id=Xqj-TTzkvTEC&q=0070494398. 
  13. ↑ 13.0 13.1 Lerner, Leonid (2011). Small-Scale Synthesis of Laboratory Reagents with Reaction Modeling. Boca Raton, Florida: CRC Press. pp. 169–177. ISBN 978-1-4398-1312-6. https://books.google.com/books?id=KaIzmQEACAAJ&q=9781439813126. 
  14. ↑ Patil, Pravin; Ahmadian-Moghaddam, Maryam; Dömling, Alexander (29 September 2020). "Isocyanide 2.0". Green Chemistry 22 (20): 6902–6911. doi:10.1039/D0GC02722G. 
  15. ↑ March, J. (1992). Advanced Organic Chemistry (4th ed.). New York, NY: Wiley. p. 723. ISBN 978-0-471-60180-7. https://archive.org/details/advancedorganicc00marc_339. 
  16. ↑ Elderfield, R. C., ed. Heterocyclic Compound. 6. New York, NY: John Wiley & Sons. p. 265. 
  17. ↑ Hurd, Charles D.; Webb, Carl N. (1925). "p-Dimethylaminobenzophenone". Organic Syntheses 7: 24. doi:10.15227/orgsyn.007.0024. 

Further reading



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