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Phosphorus trichloride

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds

                  Phosphorus trichloride
      Phosphorus trichloride Phosphorus trichloride
                         General
   Systematic name           Phosphorus trichloride
   Other names               Phosphorus(III) chloride
                             Phosphorous chloride
   Molecular formula         PCl[3]
   Molar mass                137.33 g/mol
   Appearance                colourless liquid
   CAS number                [7719-12-2]
   EINECS number             231-749-3
   MSDS                      External MSDS
                        Properties
   Density                   1.574 g/cm^3
   Solubility                Water: hydrolysis
                             Methanol: decomposes
                             Benzene: soluble
                             Chloroform: soluble
                             Diethyl ether: soluble
   Melting point             -93.6 °C (179.6 K)
   Boiling point             76.1 °C (349.3 K)
   Standard enthalpy
   of formation Δ[f]H^0[liq]
                             −319.7 kJ/ mol (liquid)
                        Structure
   Molecular geometry        Trigonal pyramidal
   Bond angle                100 °
   Bond length               P-Cl 204 pm (2.04 Å)
   Dipole moment             0.56 D
                         Hazards
   MSDS                      External MSDS
   Main hazards              Corrosive, toxic
                             releases HCl
   NFPA 704
   Flash point                ?°C
   R/S statement             R: 14-26/28-29-35-48/20
                             S: 26-36/37/39-45-7/8
   RTECS number              TH3675000
                 Supplementary data page
   Structure and
   properties                n[D] = 1.4080 (25 C)
   Thermodynamic
   data                      Phase behaviour
                             Solid, liquid, gas
   Spectral data             UV, IR, NMR, MS
                    Related compounds
   Other trichlorides        NCl[3]
                             AsCl[3]
                             SbCl[3]
   Related phosphorus
   compounds                 PCl[5]
                             POCl[3]
                             P[2]Cl[4]
   Other halogens            PF[3]
                             PBr[3]
                             PI[3]
     Except where noted otherwise, data are given for
   materials in their standard state (at 25°C, 100 kPa)
   Infobox disclaimer and references

   Phosphorus trichloride (formula PCl[3]) is the most important of the
   three phosphorus chlorides. It is an important industrial chemical,
   being used for the manufacture of organophosphorus compounds for a wide
   variety of applications.

Chemical properties

   The phosphorus in PCl[3] 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.

Redox reactions

   PCl[3] is a precursor to other phosphorus compound, undergoing
   oxidation to phosphorus pentachloride, PSCl[3], and phosphorus
   oxychloride.

   If an electric discharge is passed through a mixture of PCl[3] vapour
   and hydrogen gas, a rare chloride of phosphorus is formed, diphosphorus
   tetrachloride (P[2]Cl[4]).

PCl[3] as an electrophile

   Phosphorus trichloride is the precursor to organophosphorus compounds
   that contain one or more (P^3+) atoms, most notably phosphites and
   phosphonates. These compounds do not usually contain the chlorine atoms
   found in PCl[3].

   PCl[3] reacts rapidly and exothermically with water to form phosphorous
   acid, H[3]PO[3] and HCl. A large number of similar substitution
   reactions are known, the most important of which is the formation of
   phosphite esters by reaction with alcohols or phenols. For example,
   with phenol, triphenyl phosphite is formed:

          3 PhOH + PCl[3] → P(OPh)[3] + 3 HCl

   where "Ph" stands for phenyl group, -C[6]H[5]. Alcohols such as ethanol
   react similarly in the presence of a base such as triethylamine to give
   phosphite esters such as triethyl phosphite ( ethyl is -C[2]H[5]):

          3 C[2]H[5]OH + PCl[3] → P(OC[2]H[5])[3] + 3 HCl

   In the absence of base, however, the reaction affords a dialkyl
   phosphonate and an alkyl chloride, according to the following
   stoichiometry:

          PCl[3] + 3 C[2]H[5]OH → (C[2]H[5]O)[2]P(=O)H + C[2]H[5]Cl + 2
          HCl

   Amines, R[2]NH, form P(NR[2])[3], and thiols (RSH) form P(SR)[3]. An
   industrially relevant reaction of PCl[3] with amines is
   phosphonomethylation, which employs formaldehyde:

          R[2]NH + PCl[3] + CH[2]O → (HO)[2]P(O)CH[2]NR[2] + 3 HCl

   Aminophosphonates are widely used as sequestring and antiscale agents
   in water treatment. The large volume herbicide glyphosate is also
   produced this way. The reaction of PCl[3] with Grignard reagents and
   organolithium reagents is a useful method for the preparation of
   organic phosphines with the formula R[3]P (sometimes called phosphanes)
   such as triphenylphosphine, Ph[3]P.

          3 PhMgBr + PCl[3] → Ph[3]P + 3 MgBrCl

   Under controlled conditions PCl[3] can be used to prepare PhPCl[2] and
   Ph[2]PCl.

PCl[3] as a nucleophile

   Phosphorus trichloride has a lone pair, and therefore can act as a
   Lewis base, for example with the Lewis acids BBr[3]^ it forms a 1:1
   adduct, Br[3]B^−−^+PCl[3]. Metal complexes such as Ni(PCl[3])[4] are
   known. This Lewis basicity is exploited in one useful route to
   organophosphorus compounds:

          PCl[3] + RCl + AlCl[3] → (RPCl[3])^+ ^−AlCl[4]

   The (RPCl[3])^+ product can then be decomposed with water to produce an
   alkylphosphonic dichloride RP(=O)Cl[2].

Preparation

   World production exceeds one-third of a million tonnes^. Phosphorus
   trichloride is prepared industrially by the reaction of chlorine with a
   refluxing solution of white phosphorus in phosphorus trichloride, with
   continuous removal of PCl[3] as it is formed.

          P[4] + 6 Cl[2] → 4 PCl[3]

   Industrial production of phosphorus trichloride is controlled under the
   Chemical Weapons Convention, where it is listed in schedule 3.In the
   laboratory it may be more convenient to use the less toxic red
   phosphorus^. It is sufficiently inexpensive that it would not be
   synthesized for laboratory use.

Uses

   PCl[3] is important indirectly as a precursor to PCl[5], POCl[3] and
   PSCl[3]. which in turn enjoy many applications in herbicides,
   insecticides, plasticisers, oil additives, and flame retardants.

   For example oxidation of PCl[3] gives POCl[3], 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,

   PCl[3] 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.

   PCl[3] 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 PCl[3]^.

Precautions

   PCl[3] is toxic, with a concentration of 600 ppm being lethal in just a
   few minutes^. PCl[3] is classified as very toxic and corrosive under EU
   Directive 67/548/EEC, and the risk phrases R14, R26/28, R35 and R48/20
   are obligatory.
   Retrieved from " http://en.wikipedia.org/wiki/Phosphorus_trichloride"
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