Phosphoryl chloride

Phosphoryl chloride

Names
IUPAC name Phosphoryl trichloride
Other names Phosphorus oxychloride Phosphoric trichloride Phosphorus trichloride oxide Phosphorous(V) oxychloride Trichlorophosphate
Properties
Chemical formula	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)
Solubility in water	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
Std enthalpy of formation (ΔfHo298)	-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

Physical

Phosphoryl chloride is a colorless liquid which fumes in air.

Availability

Is sold by big chemical suppliers, but 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, especially if large amounts are done.

Preparation

Phosphoryl chloride can be prepared by oxidizing phosphorus trichloride with pure oxygen, between 20-50 °C. Air is ineffective for this reaction.

2 PCl₃ + O₂ → 2 POCl₃

Potassium chlorate can also be used as oxidizer, instead of pure oxygen.

Reaction of phosphorus pentachloride with phosphorus pentoxide will also give POCl₃:

6 PCl₅ + P₄O₁₀ → 10 POCl₃

Heating sodium chloride with phosphorus pentoxide will also give phosphorus oxychloride:

2 P₂O₅ + 3 NaCl → 3 NaPO₃ + POCl₃

Reduction of tricalcium phosphate with carbon in the presence of chlorine gas is more accessible route, although it requires high temperatures. It should be noted that chlorine and carbon monoxide can form very toxic phosgene.

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

Projects

• Make phosphate esters
• Make nitriles from amides
• Vilsmeier–Haack reaction

Handling

Safety

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

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

Relevant Sciencemadness threads

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