Phosphorus trichloride PCl3 CAS NO.7719-12-2

The phosphorus in PCl₃ is often considered to have the +3 oxidation state and the chlorine atoms are considered to be in the -1 oxidation state. Most of its reactivity is consistent with this description.

PCl₃ is important indirectly as a precursor to PCl₅, POCl₃ and PSCl₃. which in turn enjoy many applications in herbicides, insecticides, plasticisers, oil additives, and flame retardants.

For example oxidation of PCl₃ gives POCl₃, which is used for the manufacture of triphenyl phosphate and tricresyl phosphate, which find application as flame retardants and plasticisers for PVC. They are also used to make insecticides such as diazinon. Phosphonates include the herbicide glyphosate,

PCl₃ is the precursor to triphenylphosphine for the Wittig reaction, and phosphite esters which may be used as industrial intermediates, or used in the Horner-Wadsworth-Emmons reaction, both important methods for making alkenes. It can be used to make trioctylphosphine oxide (TOPO), used as an extraction agent, although TOPO is usually made via the corresponding phosphine.

PCl₃ is also used directly as a reagent in organic synthesis. It is used to convert primary and secondary alcohols into alkyl chlorides, or carboxylic acids into acyl chlorides, although thionyl chloride generally gives better yields than PCl₃.