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phosphorus trichloride

Product name phosphorus trichloride
Synonyms phosphorus (III) chloride
GOST no data
CAS 7719-12-2

Phosphorus trichloride (PCl3) is a clear, colorless, oily liquid. It fumes in humid air due to hydrolysis. It is soluble in diethyl ether, benzene, chloroform, carbon disulfide, carbon tetrachloride. Phosphorus trichloride violently reacts with water to form phosphorous acid H3PO3 and releasing hydrogen chloride:

PCl3 + 3H2O → H3PO3 + 3HCl

Its molecule has a trigonal pyramide geometry with a phosphorus atom in a vertex. P-Cl bond length is 0.204nm and Cl-P-Cl angle is 100°.

The phosphorus in PCl3 is often considered to have the +3 oxidation state. Oxidation of phosphorus trichloride results in phosphorus(V) derivatives. Thus, treatment with molecular chlorine leads to phosphorus pentachloride. This reaction is exothermic and reversible.

PCl3 + Cl2 → PCl5 ΔH=-129.7KJ/mol

Oxidation of PCl3 with oxygen results in phosphorus oxychloride POCl3 formation:

2PCl3 + O2 → 2POCl3

The reactions of phosphorus trichloride with organic compounds containing hydroxyl function may lead to a variety of products. The path of reaction and products depend on organic compound nature and process conditions. Thus, phenol and other aryl alcohols interact with PCl3 to form triaryl phosphites:

3PhOH + PCl3 → P(OPh)3 + 3HCl

Similar products (trialkyl phosphites) are obtained when aliphatic alcohols react with PCl3 in the presence of base (e.g. triethylamine). But if this reaction is conducted in neutral media, a dialkyl phosphonate and an alkyl chloride are formed:

3ROH + PCl3 → (RO)2P(=O)H + RCl + 2HCl

Phosphorus trichloride is alkylated with organometallic compounds, such as lithium, sodium or magnesium derivatives to form organic phosphines. Reaction with an excess of organometallic compound results in trisubstituted phosphine:

3BuLi + PCl3 → Bu3P + 3LiCl

Under controlled stoichiometry this reaction can be used to prepare RPCl2 and R2PCl.

Phosphorus trichloride is a very toxic compound, with a concentration of 600 ppm being lethal in just a few minutes. It causes corrosion of metal parts.

Production.

Industrially PCl3 is obtained by direct interaction of phosphorus with molecular chlorine. Process is conducted either by burning of phosphorus in atmosphere of dry chlorine or by bubbling of gaseous chlorine through solution of white phosphorus in carbon disulfide.

P4 + 6Cl2 → 4PCl3

Crude product is contaminated with phosphorus pentachloride and then purified by distillation.

Uses.

  • as a feedstock in industrial production of phosphorus pentachloride PCl5, phosphorus oxychloride POCl3 and phosphorus thiochloride PSCl3;
  • as an intermediate in manufacturing of triphenylphosphine, phosphites;
  • in a laboratory organic synthesis for preparation of alkyl chlorides from alkohols, acyl chlorides from carboxylic acids and organophosphorous compounds;
  • as a raw material in making pharmaceuticals, plasticizers for PVC, pesticides, oil additives, fire retardants, dyes, detergents and others;

  • Manufacturer(s) JSC Khimprom
    Chemical structure of phosphorus trichloride

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