| IUPAC name
| Other names
|Molar mass||208.22 g/mol|
|Melting point||160.5 °C (320.9 °F; 433.6 K)|
|Boiling point||166.8 °C (332.2 °F; 439.9 K) (sublimation)|
|Solubility|| Reacts with alcohols, carboxylic acids|
Soluble in benzene, carbon disulfide, carbon tetrachloride, chloroform, dichloromethane, liq HCl
Readily soluble in TiCl4, thionyl chloride
Sparingly soluble in cyanogen chloride, phosphoryl chloride, SnCl4, sulfuryl chloride
Insoluble in VOCl3
|Vapor pressure|| 1.11 kPa (80 °C)|
4.58 kPa (100 °C)
Std enthalpy of
|Safety data sheet||Sigma-Aldrich|
|Lethal dose or concentration (LD, LC):|
LD50 (Median dose)
|660 mg/kg (rat, oral)|
LC50 (Median concentration)
|205 mg/kg (rat)|
| Phosphorus trichloride|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Phosphorus pentachloride is a chemical compound with the formula PCl5, a phosphorus chloride. It is widely used as a chlorinating reagent in chemistry.
Phosphorus pentachloride is sensitive to water and will readily hydrolyze in the presence of moisture to give phosphoryl chloride:
- PCl5 + H2O → POCl3 + 2 HCl
If excess water is present, the hydrolysis continues until phosphoric acid is obtained:
- PCl5 + 4 H2O → H3PO4 + 5 HCl
Like phosphorus trichloride, phosphorus pentachloride is a good chlorinating agent and is capable of chlorinating carboxylic acids to acyl chlorides:
- PCl5 + R-COOH → POCl3 + R-COCl + HCl
PCl5 exists in equilibrium with PCl3 and chlorine, at 180 °C the degree of dissociation is ~40%. Because of this equilibrium, samples of PCl5 often contain elemental chlorine, which imparts a greenish coloration. Vacuum can be used to remove the two side products from the resulting pentachloride.
Phosphorus pentachloride is a fuming white solid, which reacts violently with water and alcohols. It is soluble in many organic solvents such as benzene, chlorinated carbons, dichloroacetic acid, liq. HCl, molten TeCl4, liq. SO2, slightly soluble in arsenic trichloride, liq. CO2 but insoluble in liq. Cl2.
Phosphorus pentachloride is sold by various chemical suppliers, but due to its hazards it's extremely difficult to acquire. It's best to make it yourself.
Like phosphorus trichloride, PCl5 is listed on Schedule 3 of the Chemical Weapons Convention, which means all transactions may be be monitored.
Phosphorus pentachloride can be prepared by chlorinating phosphorus trichloride with elemental chlorine.
- PCl3 + Cl2 → PCl5
Sciencemadness user Magpie was able to synthesize small amounts of PCl5, by reacting excess chlorine with white phosphorus dissolved in chloroform, using garage chemist's procedure. See the thread here.
Reacting elemental chlorine with calcium phosphate, silica and carbon at 1300 °C will give phosphorus pentachloride.
While very useful in preparing a huge variety of phosphorus compounds and more, the great toxicity of phosphorus pentachloride and its tendency to hydrolyze means you will need a good ventilation system to safely handle the chemical.
- Chlorinate organic compounds
- Make phosphoryl chloride
- Make alkyl and acyl chlorides
Phosphorus pentachloride is very corrosive and toxic. In moist air, it hydrolyzes releasing hydrochloric acid fumes, which are very corrosive.
Phosphorus pentachloride is notoriously hard to store. Sciencemadness user woelen noted that PCl5 tends to attack even teflon-lined caps over time. Ampouling is the only safe method to store this compound for long periods of time.
Phosphorus pentachloride should be neutralized with a base, such as calcium hydroxide suspension outside or in a well ventilated area. Always add small amounts of PCl5 to prevent splashing. Even so, there will be plenty of HCl fumes generated by the hydrolysis. Try not to use carbonates as neutralizing agents, as they will fizzle and cause some PCl5 to become airborne.
- North, H. B.; Thomson, J. C.; Journal of the American Chemical Society; vol. 40; (1918); p. 774 - 777
- Thomson, T.; Philosophical Magazine (1798-1977); vol. 8; (1816); p. 87 - 93