How is phosphorus pentachloride formed

Phosphorus pentachloride

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Phosphorus pentachloride is a colorless, hygroscopic crystalline mass with a caustic odor. It is mostly yellowish or greenish in color due to partial decomposition into phosphorus trichloride and chlorine.[5]

Extraction and presentation

The technical preparation of phosphorus pentachloride takes place by chlorination of phosphorus trichloride in an equilibrium reaction:

$ \ mathrm {PCl_3 \ + Cl_2 \ \ rightleftharpoons \ PCl_5} $

The reactants are reacted in lead-lined towers in a countercurrent process.[5]

Properties and use

With water the substance decomposes to phosphoric acid and hydrogen chloride:

$ \ mathrm {\ PCl_5 \ + \ 4 \ H_2O \ \ longrightarrow \ \ H_3PO_4 \ + \ 5 \ HCl} $

Even at normal temperature, more quickly when heated, the pentachloride decomposes to form phosphorus trichloride, releasing chlorine. Phosphorus pentachloride does not melt at normal pressure, but rather sublimes from around 100 ° C. In a closed apparatus it melts under overpressure at 148–160.5 ° C.[1][5]

In general, phosphorus pentachloride is used as a chlorinating agent because it gives off chlorine very easily. For example, carboxylic acids are converted to the corresponding acid chloride.

safety instructions

Phosphorus pentachloride is very toxic and reacts violently with water, metal oxides, metal powders and organic substances, generating heat and splitting off toxic gases such as phosphoryl chloride, hydrogen chloride and chlorine gas.[1] Furthermore, phosphorus pentachloride reacts with many acids and their salts to form the corresponding acid chlorides. The extremely toxic phosgene is formed from carbonates and phosphorus pentachloride.

Individual evidence

  1. 1,001,011,021,031,041,051,061,071,081,091,10Entry to CAS no. 10026-13-8 in the GESTIS substance database of the IFA, accessed on July 25, 2011 (JavaScript required).
  2. 2,02,1Entry from the CLP regulation too CAS no. 10026-13-8 in the GESTIS substance database of the IFA (JavaScript required)
  3. ↑ Since December 1, 2012, only GHS hazardous substance labeling has been permitted for substances. Until June 1, 2015, the R-phrases of this substance may still be used to classify preparations, after which the EU hazardous substance labeling is of purely historical interest.
  4. ↑ data sheet Phosphorus pentachloride at Merck, accessed April 5, 2007.
  5. 5,05,15,2A. F. Holleman (greeting), Nils Wiberg: Inorganic Chemistry Textbook. 101st, improved and greatly expanded edition. de Gruyter, Berlin et al. 1995, ISBN 3-11-012641-9, pp. 757-758.