Phosphoryl chloride

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Phosphoryl chloride
Names
IUPAC name
Phosphoryl trichloride
Other names
Phosphorus oxychloride
Phosphoric trichloride
Phosphorus trichloride oxide
Phosphorous(V) oxychloride
Trichlorophosphate
Properties
POCl3
Molar mass 153.33 g/mol
Appearance Colorless fuming liquid
Odor Pungent, acidic
Density 1.645 g/cm3
Melting point 1.25 °C (34.25 °F; 274.40 K)
Boiling point 105.8 °C (222.4 °F; 378.9 K)
Reacts
Solubility Reacts with alcohols, carboxylic acids
Soluble in benzoyl chloride, bromine, bromoacetic acid, carbon disulfide, liq. Cl2, liq. HBr, liq. HCl, hydrogen cyanide, liq. H2S, anh. nitric acid, sulfuryl chloride, liq. SO2, SnCl4
Sparingly soluble in liq. HI
Vapor pressure 40 mmHg (27.3 °C)
Thermochemistry
-615.7 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Related compounds
Related compounds
 Phosphoryl bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Phosphoryl chloride or phosphorus oxychloride is a fuming colourless liquid, widely used for the synthesis of phosphate esters. It is a colorless fuming liquid, with the formula POCl3.

Properties

Chemical

Phosphorus oxychloride reacts with water to form phosphoric acid and hydrogen chloride fumes.

POCl3 + 3 H2O → H3PO4 + 3 HCl

Reaction with alcohols and phenols gives phosphate esters:

POCl3 + 3 ROH → O=P(OR)3 + 3 HCl

Phosphoryl chloride can also act as a Lewis base, forming adducts with a variety of Lewis acids such as titanium(IV) chloride:

POCl3 + TiCl4 → POCl3·TiCl4

The aluminium chloride adduct (POCl3·AlCl3) is quite stable, and so POCl3 can be used to remove AlCl3 from reaction mixtures, for example at the end of a Friedel-Crafts reaction.

Phosphoryl chloride reacts with hydrogen bromide in the presence of Lewis-acidic catalysts to produce phosphoryl bromide.

POCl3 + 3 HBr → POBr3 + 3 HCl

Physical

Phosphoryl chloride is a colorless liquid which fumes in air.

Availability

Is sold by big chemical suppliers, but for a private individual it's next to impossible to get hold of.

Phosphoryl chloride is listed on Schedule 3 of the Chemical Weapons Convention. Transactions tend to be monitored by authorities, especially if large amounts are done.

Preparation

Phosphoryl chloride can be easily prepared by oxidizing phosphorus trichloride with pure oxygen, between 20-50 °C. Air is ineffective for this reaction, and thus pure oxygen must be used.[1][2][3]

PCl3 + ½ O2 → POCl3

Ozone has also been used successfully.[4]

Potassium chlorate can also be used as oxidizer, instead of pure oxygen.[5][6][7]

3 PCl3 + KClO3 → 3 POCl3 + KCl

Partial hydrolysis of phosphorus pentachloride with water, at very low temperatures, under vacuum is indicated to yield phosphoryl chloride. Yield is given as 88%.[8][9]

PCl5 + H2O → POCl3 + 2 HCl

Heating a mixture of anhydrous phosphoric acid and phosphorus pentachloride at 130 °C will give off fumes of POCl3:[10][11][12][13]

H3PO4 + PCl5 → POCl3 + ???

Reaction of phosphorus pentachloride with phosphorus pentoxide will also give POCl3:[14]

6 PCl5 + P4O10 → 10 POCl3

If phosphorus pentoxide is not available, boric acid or oxalic acid can also be used.

3 PCl5 + 2 H3BO3 → 3 POCl3 + B2O3 + 6 HCl
PCl5 + (COOH)2 → POCl3 + CO + CO2 + 2 HCl

Heating a chloride salt, like sodium chloride with phosphorus pentoxide at 250 °C will also give phosphorus oxychloride, although the yield is not great:[15][16]

2 P2O5 + 3 NaCl → 3 NaPO3 + POCl3

Anhydrous calcium chloride can also be used for the reaction above.

4 P2O5 + 3 CaCl2 → 3 Ca(PO3)2 + 2 POCl3

Both regents must be perfectly dry and the pentoxide must be fresh, old one tens to be degraded from moisture.

Reduction of tricalcium phosphate with carbon in the presence of chlorine gas is more accessible route, although it requires high temperatures, of around 700 °C. Yield is given as 95%.[17][18]

Ca3(PO4)2 + 6 C + 6 Cl2 → 2 POCl3 + 3 CaCl2 + 6 CO

It should be noted that chlorine and carbon monoxide can form very toxic phosgene, so this route, while accessible, may not be safe.

There are several other routes to this compound described in literature, with varying results.

Reaction of phosphorous pentoxide with nitrosyl chloride, in a porcelain tube at 1000-1100 °C, will yield phosphoryl chloride and nitrogen trichloride. The yield of this route is described as "poor".[19][20]

PCl5 + NOCl → POCl3 + NCl3

Phosphoramidic acid (H2PO3NH2) will also react with phosphorus pentachloride to give POCl3. This is done by refluxing the two reagents in tetrachlorethane, for 4 hours. The raw product is purified under vacuum. Yield is given as 88%.[21]

PCl5 + (OH)2P(=O)NH2 → POCl3 + PCl3=NP(=O)Cl2 + HCl

Sulfur trioxide has also been used.[22]

PCl5 + 2 SO3 → POCl3 + S2Cl2O5

Projects

  • Make phosphate esters
  • Make nitriles from amides
  • Remove AlCl3 from reaction products
  • Vilsmeier–Haack reaction

Handling

Safety

Phosphorus oxychloride is very corrosive and toxic, and its fumes are highly corrosive and toxic. Wear proper protection when handling the compound. Only work in a fumehood or in a well ventilated place.

Symptoms of exposure to this compound may take several hours before they appear.

Storage

Phosphoryl chloride should be stored in Schlenk flasks, as they're the best storage containers for air and water sensitive reagents.

Disposal

Phosphoryl chloride should be neutralized with a base, such as calcium hydroxide suspension outside or in a well ventilated area. Always add small amounts of POCl3 to prevent splashing. Try not to use carbonates, as they will fizzle and cause some POCl3 to become airborne. Since small amounts of HCl fumes will be formed anyway, use a lidded container in case of runaway.

References

  1. ↑ Berthelot, M.; Ann. Chim. Phys.; vol. 15; (1878); p. 209
  2. ↑ Patent; Mugdan, M.; Sixt, J.; Consortium fuer Elektrochemische Industrie G.m.b.H.; DE624884; (1936); C. I; (1936); p. 3559
  3. ↑ Bettermann, Gerhard; Krause, Werner; Riess, Gerhard; Hofmann, Thomas (2000). "Phosphorus Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry
  4. ↑ Remsen, I.; Am. J. Sci.; vol. 11; (1876); p. 365 - 369
  5. ↑ Schiff, H.; Liebigs Annalen der Chemie; vol. 106; (1858); p. 116 - 118
  6. ↑ Dervin, E.; Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences; vol. 97; (1883); p. 576 - 578
  7. ↑ Ullmann, F.; Fornaro, A.; Ber.; vol. 34; (1901); p. 2172 - 2173
  8. ↑ Oddo, G.; Gazzetta Chimica Italiana; vol. 29; nb. II; (1900); p. 330 - 343
  9. ↑ Sammons; Frey; Bruzik; Tsai; Journal of the American Chemical Society; vol. 105; nb. 16; (1983); p. 5455 - 5461
  10. ↑ Fejes, P.; Magyar Tudomanyos Akademia Kozponti Fizikai Kutato Intezetenek Kozlemenyei; (1959); p. 18716; Magyar Tudomanyos Akademia Kozponti Fizikai Kutato Intezetenek Kozlemenyei; vol. 3; (1955); p. 535 - 542
  11. ↑ Casida, J. E.; Acta Chemica Scandinavica (1947-1973); vol. 12; (1958); p. 1691 - 1692
  12. ↑ Kalinsky, J. L.; Weinstein, A.; Journal of the American Chemical Society; vol. 76; (1954); p. 5882 - 5882
  13. ↑ Murray, D. H.; Spinks, J. W. T.; Canadian Journal of Chemistry; vol. 30; (1952); p. 497 - 497
  14. ↑ Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. New York: McGraw-Hill. p. 709
  15. ↑ Tarbutton, G.; Egan, E. P.; Frary, S. G.; Journal of the American Chemical Society; vol. 63; (1941); p. 1782 - 1789
  16. ↑ Turning Salt Into Phosphoryl Chloride: The Chemical That Hospitalized Me
  17. ↑ Kato, Y.; Fujino, S.; Kogyo Kagaku Zasshi; vol. 36; (1933); p. B132
  18. ↑ Lerner, Leonid (2011). Small-Scale Synthesis of Laboratory Reagents with Reaction Modeling. Boca Raton, Florida: CRC Press. pp. 169–177
  19. ↑ Sidgwick, N. V.; The chemical Elements and their Compounds, Bd. 1, Oxford 1950, S. 705
  20. ↑ Noyes, W. A.; Journal of the American Chemical Society; vol. 35; (1913); p. 767 - 767
  21. ↑ Becke-Goehring, M.; Mann, T.; Euler, H. D.; Chemische Berichte; vol. 94; (1961); p. 193 - 198
  22. ↑ Paul, R. C.; Arora, C. L.; Malhotra, K. C.; Indian J. Chem.; vol. 9; (1971); p. 473 - 476

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