Phosphorus halides 1937128 211648709 2008-05-11T12:31:18Z 131.111.8.102 /* See also */ Phosphorus Chlordies goes straight back this page There are three series of binary '''phosphorus halides''', containing [[phosphorus]] in the [[oxidation state]]s +5, +3 and +2. All twelve compounds have been described, in varying degrees of detail, although serious doubts have been cast on the existence of PI<sub>5</sub>. {{fn|(1)}} == Oxidation state +5 (PX<sub>5</sub>) == {| class="wikitable" |- ! [[Chemical formula]] ! [[CAS number]] ! [[Melting point]] ! [[Boiling point]] ! P&ndash;X<sub>''ax''</sub> [[bond length]] ! P&ndash;X<sub>''eq''</sub> bond length ! X<sub>''ax''</sub>&ndash;P&ndash;X<sub>''eq''</sub> [[bond angle]] ! X<sub>''ax''</sub>&ndash;P&ndash;X<sub>''ax''</sub> bond angle |- | [[Phosphorus pentafluoride|PF<sub>5</sub>]] | [7647-19-0] | -93.7°C | -84.5°C | 153 pm | 158 pm | 120° | 90° |- | [[Phosphorus pentachloride|PCl<sub>5</sub>]] | [10026-13-8] | 167°C | 160°C | &nbsp; | &nbsp; | &nbsp; | &nbsp; |- | [[Phosphorus pentabromide|PBr<sub>5</sub>]] | [7789-69-7] | ~106°C ''d'' | &nbsp; | &nbsp; | &nbsp; | &nbsp; | &nbsp; |- | PI<sub>5</sub> | &nbsp; | colspan=6| ''See'' [[#Notes|''Note 1.'']] |} [[Phosphorus pentafluoride]] is a relatively inert gas, notable as a mild [[Lewis acid]] and a [[fluoride]] ion acceptor. It is fluxional molecule. [[Phosphorus pentachloride]] and [[phosphorus pentabromide]] are ionic in the solid and liquid states, and are best described as PX<sub>4</sub><sup>+</sup>PX<sub>6</sub><sup>&ndash;</sup>. They are widely used as chlorinating and brominating agents in organic chemistry. == Oxidation state +3 (PX<sub>3</sub>) == {| class="wikitable" |- ! [[Chemical formula]] ! [[CAS number]] ! [[Melting point]] ! [[Boiling point]] ! P&ndash;X bond length ! X&ndash;P&ndash;X bond angle ! [[Dipole moment]] |- | [[Phosphorus trifluoride|PF<sub>3</sub>]] | [7783-55-3] | -151.5°C | -101.8°C | 156 pm | 96.3° | 1.03 D |- | [[Phosphorus trichloride|PCl<sub>3</sub>]] | [7719-12-2] | -93.6°C | 76.1°C | 204 pm | 100° | 0.56 D |- | [[Phosphorus tribromide|PBr<sub>3</sub>]] | [7789-60-8] | -41.5°C | 173.2°C | 222 pm | 101° | &nbsp; |- | [[Phosphorus triiodide|PI<sub>3</sub>]] | [13455-01-1] | 61.2°C | 227°C | 243 pm | 102° | &nbsp; |} The phosphorus(III) halides are the best known of the three series. They are usually prepared by direct reaction of the elements, or by [[transhalogenation]]. [[Phosphorus trifluoride]] is used as a [[ligand]] in [[coordination chemistry]], where it resembles [[carbon monoxide]]. [[Phosphorus trichloride]] is a major industrial chemical and widely-used starting material for phosphorus chemistry. [[Phosphorus tribromide]] is used in organic chemistry to convert [[alcohol]]s to [[Alkyl halide|alkyl bromides]] and [[carboxylic acid]]s to [[Acyl halide|acyl bromides]] (''e.g.'' in the [[Hell-Volhard-Zelinsky reaction]]). [[Phosphorus triiodide]] also finds use in organic chemistry, as a mild oxygen acceptor. The trihalides are fairly readily oxidized by [[chalcogen]]s to give the corresponding [[#Oxyhalides and thiohalides|oxyhalides]] or equivalents. == Oxidation state +2 (P<sub>2</sub>X<sub>4</sub>) == {| class="wikitable" |- ! [[Chemical formula]] ! [[CAS number]] ! [[Melting point]] ! [[Boiling point]] ! P&ndash;X bond length ! P&ndash;P bond length ! X&ndash;P&ndash;X bond angle ! X&ndash;P&ndash;P bond angle |- | [[Diphosphorus tetrafluoride|P<sub>2</sub>F<sub>4</sub>]] | [13824-74-3] | -86.5°C | -6.2°C | 159 pm | 228 pm | 99.1° | 98.4° |- | [[Diphosphorus tetrachloride|P<sub>2</sub>Cl<sub>4</sub>]] | [13467-91-1] | -28°C | ~180°C ''d'' | &nbsp; | &nbsp; | &nbsp; | &nbsp; |- | [[Diphosphorus tetrabromide|P<sub>2</sub>Br<sub>4</sub>]] | [24896-99-3] | colspan=6| ''poorly characterized'' |- | [[Diphosphorus tetraiodide|P<sub>2</sub>I<sub>4</sub>]] | [13455-00-0] | 125.5°C | ''d'' | 248 pm | 221 pm | 102.3° | 94.0° |} Phosphorus(II) halides may be prepared by passing an [[electric discharge]] through a mixture of the trihalide vapour and [[hydrogen]] gas. They are of purely academic interest at the present time. [[Diphosphorus tetrabromide]] is particularly poorly described. == Oxyhalides and thiohalides == {| class="wikitable" |- ! [[Chemical formula]] ! [[CAS number]] ! [[EINECS number]] ! [[Melting point]] ! [[Boiling point]] ! [[Density]] ! [[Refractive index]] ! [[Dipole moment]] |- | [[Phosphorus oxyfluoride|POF<sub>3</sub>]] | ? | ? | −39.1°C | −39.7°C | ? | ? | ? |- | [[Phosphorus oxychloride|POCl<sub>3</sub>]] | [10025-87-3] | 233-046-7 | 1.2°C | 105.1°C | 1.675 g/cm<sup>3</sup> | 1.461 | 2.54 D |- | [[Phosphorus oxybromide|POBr<sub>3</sub>]] | [7785-59-5] | 232-177-7 | 56°C | 192°C | 2.82 g/cm<sup>3</sup> | ? | ? |- | [[Phosphorus oxyiodide|POI<sub>3</sub>]] | ? | ? | 53°C | &ndash; | ? | ? | ? |- | [[Thiophosphoryl fluoride|PSF<sub>3</sub>]] | ? | ? | −148.8°C | −52.2°C | ? | ? | ? |- | [[Thiophosphoryl chloride|PSCl<sub>3</sub>]] | [3982-91-0] | 223-622-6 | -35°C | 125°C | 1.668 g/cm<sup>3</sup> | 1.555 | ? |- | [[Thiophosphoryl bromide|PSBr<sub>3</sub>]] | ? | ? | 37.8°C | 212°C ''decomp'' | ? | ? | ? |- | [[Thiophosphoryl iodide|PSI<sub>3</sub>]] | ? | ? | 48°C | ''decomp'' | ? | ? | ? |- |} The '''oxyhalides''' may be prepared from the corresponding trihalides by reaction with [[organic peroxide]]s or [[ozone]]: they are sometimes referred to as '''phosphoryl halides'''. The '''thiohalides''', also known as '''thiophosphoryl halides''' may be prepared from the trihalides by reaction with elemental [[sulfur]] in an inert solvent. The corresponding selenohalides are also known. The oxyhalides and thiohalides are significantly more [[Electrophile|electrophilic]] than the corresponding phosphorus(III) species, and present a significant [[toxic]] hazard. == See also == == References == * [http://www.webelements.com/ WebElements] * [http://webbook.nist.gov/chemistry/ NIST Standard Reference Database] * N. N. Greenwood & A. Earnshaw, ''Chemistry of the Elements'' (2nd ed.), Butterworth-Heinemann, Oxford, '''1997'''. == Notes == #I. Tournieporth & T. Klapötke, ''J. Chem. Soc.'', ''Chem. Commun.'' '''1990''', 132. [[Category:Phosphorus compounds]] [[Category:Nonmetal halides]]