Difference between revisions of "Phosphoryl chloride"

Latest revision as of 17:44, 16 June 2024

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

Relevant Sciencemadness threads

• phosphorus oxychloride (POCl3)
• Phosphoryl chloride
• POCL3-Phosphorus Oxychloride Synthesis
• POCl3 from Phosgene and Phosphorus pentoxide
• POCL3-Phosphorus Oxychloride