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phosphorus pentachloride

Product name phosphorus pentachloride
Synonyms phosphorous (V) chloride
pentachlorophosphorane
pentachlorophosphorus
GOST no data
CAS 10026-13-8

Phosphorus pentachloride PCl5 is a colorless crystalline solid with a greenish coloration. It fumes in humid air due to hydrolysis. It is soluble in carbon tetrachloride, carbon disulfide, benzene, diethyl ether. Phosphorus pentachloride violently reacts with water releasing a lot of heat. The first hydrolysis product is phosphorus oxychloride POCl3. In hot water, hydrolysis proceeds completely to ortho-phosphoric acid:

PCl5 + 4H2O --> H3PO4 + 5HCl

Phosphorus pentachloride molecule in gaseous and molten phase or in solution has a trigonal bipiramidal (D3h) symmetry with a P atom in the base. Crystals are built of tetrahedral cations PCl4+ and octahedral anions PCl6-. Being heated above 300°C it almost completely decomposes into PCl3 and Cl2.

PCl5 is very reactive compound. The most interesting its reactions are different chlorinations. It can be used both for oxidative and substitutive chlorination. Phosphorus pentachloride converts carboxylic acids into acyl chlorides:

RC(O)OH + PCl5 --> RC(O)Cl + POCl3 + HCl

Interaction with alcohols leads to corresponding chlorides. It reacts with carbonyl compounds substituting C=O group with geminal dichloride CCl2. Being added to olefins (e.g. styrene or vinyl acetate) phosphorus pentachloride forms adducts which after hydrolysis results in phosphonic acid derivatives:

RCH=CH2 + PCl5 --> RCHClCH2PCl4

The reaction of PCl5 with phosphorus anhydride produces phosphorus oxychloride:

6PCl5 + P4O10 --> 10POCl3

Production.

Phosphorus pentachloride is manufactured by direct chlorination of phosphorus trichloride PCl3 or by bubbling of gaseous chlorine through solution of PCl3 in carbon disulfide. This reaction is reversible. Because of this equilibrium, PCl5 contains chlorine, which imparts a greenish coloration.

PCl3 + Cl2 --> PCl5 ΔH=-129.7KJ/mol

Uses.

  • as a chlorination agent used in preparation of different products in industry and laboratory synthesis (e.g. dyes, pharmaceuticals and others);
  • as an intermediate in manufacturing phosphorus acid chloroanhydrides and phosphonic acid derivatives;
  • as a dehydrating agent;
  • as an intermediate for making organophosphorus pesticides, water treatment agents, phosphite antioxidants, lube oil and paint additives;
  • to produce plasticizers and stabilizers for plastics and elastomers;
  • to improve grain structure in metal casting;
  • to prepare lithium hexafluorophosphate - an electrolyte in lithium-ione batteries:

    PCl5 + 6LiCl --> LiPF6 + 5LiCl

  • Manufacturer(s) no data
    Chemical structure of phosphorus pentachloride

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