Phosphorus halides
Encyclopedia
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 PI5.
In the gas phase the phosphorus pentahalides have trigonal bipyramidal molecular geometry as explained by VSEPR theory
.
Phosphorus pentafluoride
is a relatively inert gas, notable as a mild Lewis acid
and a fluoride
ion acceptor. It is a fluxional molecule in which the axial (ax) and equatorial (eq) fluorine atoms interchange positions by the Berry pseudorotation mechanism.
Phosphorus pentachloride and phosphorus pentabromide
are ionic in the solid and liquid states, PCl5 is formulated PCl4+PCl6– and in contrast PBr5 is formulated PBr4+ Br−. They are widely used as chlorinating and brominating agents in organic chemistry.
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 bromides and carboxylic acid
s to 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 or equivalents.
Phosphorus(II) halides may be prepared by passing an electric discharge
through a mixture of the trihalide vapour and hydrogen
gas. The relatively stable P2I4 is known to have a trans, bent configuration similar to hydrazine
and finds some uses in organic syntheses, the others are of purely academic interest at the present time. Diphosphorus tetrabromide is particularly poorly described.
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 electrophilic
than the corresponding phosphorus(III) species, and present a significant toxic hazard.
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
in the oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
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 PI5.
Oxidation state +5 (PX5)
| Chemical formula Chemical formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound.... |
CAS number | Melting point Melting point The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure... |
Boiling point Boiling point The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.... |
P–Xax bond length Bond length - Explanation :Bond length is related to bond order, when more electrons participate in bond formation the bond will get shorter. Bond length is also inversely related to bond strength and the bond dissociation energy, as a stronger bond will be shorter... |
P–Xeq bond length | Xax–P–Xeq bond angle | Xax–P–Xax bond angle |
|---|---|---|---|---|---|---|---|
| PF5 Phosphorus pentafluoride Phosphorus pentafluoride, PF5, is a phosphorus halide. It's a colourless gas at room temperature and pressure.-Structure:Single-crystal X-ray studies indicate PF5 molecule has two distinct P−F bonds : P−Fax = 158.0 pm and P−Feq = 152.2 pm... |
[7647-19-0] | -93.7°C | -84.5°C | 153 pm | 158 pm | 120° | 90° |
| PCl5 | [10026-13-8] | 167°C | 160°C | 202 pm | 214 pm | 120° | 90° |
| PBr5 Phosphorus pentabromide Phosphorus pentabromide is a reactive, yellow solid of formula PBr5, which has the structure PBr4+ Br− in the solid state but in the vapor phase is completely dissociated to PBr3 and Br2. Rapid cooling of this phase to 15 K leads to formation of an ionic species [PBr4]+[Br3]-.It can be used in... |
[7789-69-7] | ~106°C d | |||||
| PI5 | See Note 1. | ||||||
In the gas phase the phosphorus pentahalides have trigonal bipyramidal molecular geometry as explained by VSEPR theory
VSEPR theory
Valence shell electron pair repulsion theory is a model in chemistry used to predict the shape of individual molecules based upon the extent of electron-pair electrostatic repulsion. It is also named Gillespie–Nyholm theory after its two main developers...
.
Phosphorus pentafluoride
Phosphorus pentafluoride
Phosphorus pentafluoride, PF5, is a phosphorus halide. It's a colourless gas at room temperature and pressure.-Structure:Single-crystal X-ray studies indicate PF5 molecule has two distinct P−F bonds : P−Fax = 158.0 pm and P−Feq = 152.2 pm...
is a relatively inert gas, notable as a mild Lewis acid
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
and a fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
ion acceptor. It is a fluxional molecule in which the axial (ax) and equatorial (eq) fluorine atoms interchange positions by the Berry pseudorotation mechanism.
Phosphorus pentachloride and phosphorus pentabromide
Phosphorus pentabromide
Phosphorus pentabromide is a reactive, yellow solid of formula PBr5, which has the structure PBr4+ Br− in the solid state but in the vapor phase is completely dissociated to PBr3 and Br2. Rapid cooling of this phase to 15 K leads to formation of an ionic species [PBr4]+[Br3]-.It can be used in...
are ionic in the solid and liquid states, PCl5 is formulated PCl4+PCl6– and in contrast PBr5 is formulated PBr4+ Br−. They are widely used as chlorinating and brominating agents in organic chemistry.
Oxidation state +3 (PX3)
| Chemical formula Chemical formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound.... |
CAS number | Melting point Melting point The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure... |
Boiling point Boiling point The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.... |
P–X bond length | X–P–X bond angle | Dipole moment Dipole moment Dipole moment can be defined as the product of magnitude of charge & distance of separation between the charges.Dipole moment may refer to:*Electric dipole moment, the measure of the electrical polarity of a system of charges... |
|---|---|---|---|---|---|---|
| PF3 Phosphorus trifluoride Phosphorus trifluoride , is a colorless and odorless gas. It is highly toxic and it reacts slowly with water. Its main use is as a ligand in metal complexes... |
[7783-55-3] | -151.5°C | -101.8°C | 156 pm | 96.3° | 1.03 D |
| PCl3 Phosphorus trichloride Phosphorus trichloride is a chemical compound of phosphorus and chlorine, having chemical formula PCl3. Its shape is trigonal pyramidal. It is the most important of the three phosphorus chlorides. It is an important industrial chemical, being used for the manufacture of organophosphorus compounds... |
[7719-12-2] | -93.6°C | 76.1°C | 204 pm | 100° | 0.56 D |
| PBr3 Phosphorus tribromide Phosphorus tribromide is a colourless liquid with the formula PBr3. It fumes in air due to hydrolysis and has a penetrating odour. It is widely used in the laboratory for the conversion of alcohols to alkyl bromides.-Preparation:... |
[7789-60-8] | -41.5°C | 173.2°C | 222 pm | 101° | |
| PI3 Phosphorus triiodide Phosphorus triiodide is an unstable red solid which reacts violently with water. It is a common misconception that PI3 is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides. It is also a powerful... |
[13455-01-1] | 61.2°C | 227°C | 243 pm | 102° |
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
Phosphorus trifluoride
Phosphorus trifluoride , is a colorless and odorless gas. It is highly toxic and it reacts slowly with water. Its main use is as a ligand in metal complexes...
is used as a ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
in coordination chemistry, where it resembles carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
. Phosphorus trichloride
Phosphorus trichloride
Phosphorus trichloride is a chemical compound of phosphorus and chlorine, having chemical formula PCl3. Its shape is trigonal pyramidal. It is the most important of the three phosphorus chlorides. It is an important industrial chemical, being used for the manufacture of organophosphorus compounds...
is a major industrial chemical and widely-used starting material for phosphorus chemistry. Phosphorus tribromide
Phosphorus tribromide
Phosphorus tribromide is a colourless liquid with the formula PBr3. It fumes in air due to hydrolysis and has a penetrating odour. It is widely used in the laboratory for the conversion of alcohols to alkyl bromides.-Preparation:...
is used in organic chemistry to convert alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s to alkyl bromides and carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
s to acyl bromides
Acyl halide
An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group....
(e.g. in the Hell-Volhard-Zelinsky reaction). Phosphorus triiodide
Phosphorus triiodide
Phosphorus triiodide is an unstable red solid which reacts violently with water. It is a common misconception that PI3 is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides. It is also a powerful...
also finds use in organic chemistry, as a mild oxygen acceptor.
The trihalides are fairly readily oxidized by chalcogen
Chalcogen
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
s to give the corresponding oxyhalides or equivalents.
Oxidation state +2 (P2X4)
| Chemical formula Chemical formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound.... |
CAS number | Melting point Melting point The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure... |
Boiling point Boiling point The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.... |
P–X bond length | P–P bond length | X–P–X bond angle | X–P–P bond angle |
|---|---|---|---|---|---|---|---|
| P2F4 | [13824-74-3] | -86.5°C | -6.2°C | 159 pm | 228 pm | 99.1° | 98.4° |
| P2Cl4 | [13467-91-1] | -28°C | ~180°C d | ||||
| P2Br4 | [24896-99-3] | poorly characterized | |||||
| P2I4 Diphosphorus tetraiodide Diphosphorus tetraiodide, P2I4, is an orange crystalline solid, and a versatile reducing agent. The phosphorus atom has an NMR chemical shift of about +100 ppm... |
[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
Electric discharge
Electric discharge describes any flow of electric charge through a gas, liquid or solid. Electric discharges include:*Electric glow discharge*Electric arc*Electrostatic discharge*Electric discharge in gases*Leader *Partial discharge...
through a mixture of the trihalide vapour and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas. The relatively stable P2I4 is known to have a trans, bent configuration similar to hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
and finds some uses in organic syntheses, the others are of purely academic interest at the present time. Diphosphorus tetrabromide is particularly poorly described.
Oxyhalides and thiohalides
| Chemical formula Chemical formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound.... |
CAS number | EINECS number | Melting point Melting point The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure... |
Boiling point Boiling point The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.... |
Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... |
Refractive index Refractive index In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium.... |
Dipole moment Dipole moment Dipole moment can be defined as the product of magnitude of charge & distance of separation between the charges.Dipole moment may refer to:*Electric dipole moment, the measure of the electrical polarity of a system of charges... |
|---|---|---|---|---|---|---|---|
| POF3 | ? | ? | −39.1°C | −39.7°C | ? | ? | ? |
| POCl3 | [10025-87-3] | 233-046-7 | 1.2°C | 105.1°C | 1.675 g/cm3 | 1.461 | 2.54 D |
| POBr3 | [7785-59-5] | 232-177-7 | 56°C | 192°C | 2.82 g/cm3 | ? | ? |
| POI3 | ? | ? | 53°C | – | ? | ? | ? |
| PSF3 | ? | ? | −148.8°C | −52.2°C | ? | ? | ? |
| PSCl3 Thiophosphoryl chloride Thiophosphoryl chloride is an inorganic compound with the formula PSCl3. Thiophosphoryl chloride, PSCl3, is a fuming, colorless liquid with a pungent odor... |
[3982-91-0] | 223-622-6 | -35°C | 125°C | 1.668 g/cm3 | 1.555 | ? |
| PSBr3 | ? | ? | 37.8°C | 212°C decomp | ? | ? | ? |
| PSI3 | ? | ? | 48°C | decomp | ? | ? | ? |
The oxyhalides may be prepared from the corresponding trihalides by reaction with organic peroxide
Organic peroxide
Organic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RCOOR. The O-O bond easily breaks and forms free radicals of the form RO·...
s or ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
: 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
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
in an inert solvent. The corresponding selenohalides are also known.
The oxyhalides and thiohalides are significantly more electrophilic
Electrophile
In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...
than the corresponding phosphorus(III) species, and present a significant toxic hazard.