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Phosphoryl chloride

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds

                          Phosphoryl chloride
                          Phosphoryl chloride
                                General
                 Systematic name        Phosphoryl chloride or
                                  Phosphorus oxide trichloride
                     Other names        Phosphorus oxychloride
                                        Phosphoric trichloride
               Molecular formula                       POCl[3]
                      Molar mass                  153.33 g/mol
                      Appearance     Clear, colourless liquid,
                                            fumes in moist air
                      CAS number                  [10025-87-3]
                               Properties
               Density and phase          1.645 g/cm^3, liquid
             Solubility in water                        Reacts
                   Melting point             1.25 °C (274.4 K)
                   Boiling point            105.8 °C (379.0 K)
                       Viscosity                 ? c P at ? °C
                               Structure
                 Molecular shape                   tetrahedral
                   Dipole moment                        2.54 D
                                Hazards
                            MSDS                 External MSDS
                    Main hazards             Highly corrosive,
                                            lachrymator, toxic
                   R/S statement       R: 14-22-26-29-35-48/23
                                                   S:26-45-7/8
                    RTECS number                     TH4897000
                        Supplementary data page
          Structure & properties                 n, ε[r], etc.
              Thermodynamic data               Phase behaviour
                                            Solid, liquid, gas
                   Spectral data               UV, IR, NMR, MS
                           Related compounds
               Related compounds Thiophosphoryl chloride

                                                     Phosphorus oxybromide
                                                    Phosphorus trichloride
                                                  Phosphorus pentachloride
               Except where noted otherwise, data are given for
          materials in their standard state (at 25°C, 100 kPa)
                             Infobox disclaimer and references

   Phosphoryl chloride (commonly called phosphorus oxychloride) is a
   colourless liquid with the formula POCl[3]. It hydrolyses in moist air
   to phosphoric acid to release choking fumes of hydrogen chloride. It is
   manufactured industrially on a large scale from phosphorus trichloride
   and oxygen or phosphorus pentoxide. It is mainly used to make phosphate
   esters such as tricresyl phosphate.

Structure

   Like phosphate, phosphoryl chloride is tetrahedral in shape. It
   features three P-Cl bonds and one very strong P=O double bond, with an
   estimated bond dissociation energy of 533.5 kJ/mol. On the basis of
   bond length and electronegativity, the Schomaker-Stevenson rule
   suggests that the double bond form is very dominant (in contrast with
   POF[3]). The P=O bond does not resemble the π bond in a carbonyl group
   as in a ketone. The appropriate description of the P-O interaction is a
   matter of long discussion. Older textbooks favour a description that
   invokes participation of the d-orbitals on phosphorus. Some of these
   d-orbitals project toward the O atom, overlapping with p-orbitals on
   oxygen. More modern texts seem to favour a description where the P-O π
   bonding involves the sigma* components of the P-Cl bonds. These
   descriptions do not consider a role for d-orbitals.

                      where pm = picometers

Chemical properties

   POCl[3] reacts with water and alcohols to give phosphoric acid or
   phosphate esters, respectively, for example

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

   If the water is replaced by an alcohol, the trialkyl phosphate esters
   result. Such reactions are often performed in the presence of an HCl
   acceptor such as pyridine or an amine. If POCl[3] is heated with an
   excess of a phenol ( ArOH) in the presence of a Lewis acid catalyst
   such as magnesium chloride a triaryl phosphate ester is formed, for
   example:

          3 C[6]H[5]OH + O=PCl[3] → O=P(OC[6]H[5])[3] + 3 HCl

   POCl[3] can also act as a Lewis base, forming adducts with a variety of
   Lewis acids such as titanium tetrachloride:

          Cl[3]P^+-O^− + TiCl[4] → Cl[3]P^+-O-^−TiCl[4]

   The aluminium chloride adduct (POCl[3]·AlCl[3]) is quite stable, and so
   POCl[3] can be used to remove AlCl[3] completely from reaction mixtures
   at the end of a Friedel-Crafts reaction. POCl[3] reacts with hydrogen
   bromide in the presence of AlCl[3] to produce POBr[3].

Preparation

   Phosphoryl chloride can be prepared by the reaction of phosphorus
   trichloride with oxygen at 20-50 °C (air is ineffective):

   2 PCl[3] + O[2] → 2 O=PCl[3]

   An alternative synthesis involves the reaction of phosphorus
   pentachloride and phosphorus pentoxide. Since these compounds are both
   solids, a convenient way of performing the reaction is to chlorinate a
   mixture of PCl[3] and P[4]O[10], which generates the PCl[5] in situ. As
   the PCl[3] is consumed, the POCl[3] becomes the reaction solvent.

   6 PCl[3] + 6 Cl[2] → 6 PCl[5]

   6 PCl[5] + P[4]O[10] → 10 POCl[3]

   Phosphorus pentachloride also forms POCl[3] by reaction with water, but
   this reaction is less easily controlled than the above reaction.

Uses

   The most important use for phosphoryl chloride is in the manufacture of
   triarylphosphate esters (as described above) such as triphenyl
   phosphate and tricresyl phosphate. These esters have been used for many
   years as flame retardants and plasticisers for PVC. Meanwhile trialkyl
   esters such as tributyl phosphate (made similarly from butan-1-ol) are
   used as liquid-liquid extraction solvents in nuclear reprocessing and
   elsewhere.

   In the laboratory, POCl[3] is widely used as a dehydrating agent, for
   example the conversion of amides to nitriles. Similarly, certain cyclic
   amides can be cyclised to dihydro isoquinoline derivatives using the
   Bischler-Napieralski reaction.
   Two uses for phosphorus oxychloride in organic chemistry

   Such reactions are believed to go via an imidoyl chloride; in certain
   cases where it is stable, the imidoyl chloride is the final product.
   For example pyridones and pyrimidones can be converted to chloro-
   derivatives of pyridines and pyrimidines, which are important
   intermediates in the pharmaceutical industry. Likewise barbituric acid
   is converted to 2,4,6-trichloropyrimidine.^ by reaction with POCl[3] at
   140 °C.

   Related to this chemistry is the use of POCl[3] in acylation of
   activated aromatic rings via the Vilsmeier-Haack reaction to produce
   aryl aldehydes and ketones. The reaction most often uses a formamide
   such as DMF or N-phenyl-N-methylformamide, and it produces an iminium
   salt which is easily hydrolysed to the aldehyde upon workup. For
   example anthracene gives 9-anthraldehyde:
   Vilsmeier-Haack formylation of anthracene
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