Phosphorus trichloride is an
inorganic compound with the
chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...
PCl
3. A colorless liquid when pure, it is an important
industrial chemical, being used for the manufacture of
phosphite
The general structure of a phosphite ester showing the lone pairs on the P
In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of a ...
s and other
organophosphorus compounds. It is toxic and reacts readily with water to release
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
.
History
Phosphorus trichloride was first prepared in 1808 by the French chemists
Joseph Louis Gay-Lussac
Joseph Louis Gay-Lussac (, , ; 6 December 1778 – 9 May 1850) was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen (with Alexander von Humboldt), for two laws ...
and
Louis Jacques Thénard
Louis Jacques Thénard (4 May 177721 June 1857) was a French chemist.
Life
He was born in a farm cottage near Nogent-sur-Seine in the Champagne district
the son of a farm worker. In the post-Revolution French educational system , most boys rec ...
by heating
calomel
Calomel is a mercury chloride mineral with formula Hg2Cl2 (see mercury(I) chloride). The name derives from Greek ''kalos'' (beautiful) and ''melas'' (black) because it turns black on reaction with ammonia. This was known to alchemists.
Calomel ...
(Hg
2Cl
2) with
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
. Later during the same year, the English chemist
Humphry Davy
Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for t ...
produced phosphorus trichloride by burning phosphorus in chlorine gas.
Preparation
World production exceeds one-third of a million
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s. Phosphorus trichloride is prepared industrially by the reaction of
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
with
white phosphorus
Elemental phosphorus can exist in several allotropes, the most common of which are white and red solids. Solid violet and black allotropes are also known. Gaseous phosphorus exists as diphosphorus and atomic phosphorus.
White phosphorus
White ...
, using phosphorus trichloride as the solvent. In this continuous process PCl
3 is removed as it is formed in order to avoid the formation of PCl
5.
:P
4 + 6 Cl
2 → 4 PCl
3
Structure and spectroscopy
It has a trigonal pyramidal shape. Its
31P
NMR
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with ...
spectrum exhibits a singlet around +220 ppm with reference to a phosphoric acid standard.
Reactions
The
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
in PCl
3 is often considered to have the +3
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
and the
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
atoms are considered to be in the −1 oxidation state. Most of its reactivity is consistent with this description.
Oxidation
PCl
3 is a precursor to other phosphorus compounds, undergoing
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
to
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...
(PCl
5),
thiophosphoryl chloride
Thiophosphoryl chloride is an inorganic compound with the formula PSCl3.Spilling, C. D. "Thiophosphoryl Chloride" in Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons, Weinheim, 2001. . Article Online Posting Date: April 15, 2001. ...
(PSCl
3), or
phosphorus oxychloride
Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from pho ...
(POCl
3).
PCl3 as an electrophile
Phosphorus trichloride is the precursor to
organophosphorus compounds that contain one or more P(III) atoms, most notably phosphites and phosphonates. These compounds do not usually contain the chlorine atoms found in PCl
3.
PCl
3 reacts vigorously with
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
to form
phosphorous acid
Phosphorous acid (or phosphonic acid (singular)) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in th ...
(H
3PO
3) and
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
:
:PCl
3 + 3 H
2O → H
3PO
3 + 3 HCl
A large number of similar substitution reactions are known, the most important of which is the formation of
phosphite
The general structure of a phosphite ester showing the lone pairs on the P
In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of a ...
s by reaction with
alcohols and
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...
s. For example, with
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...
,
triphenyl phosphite is formed:
:3 PhOH + PCl
3 → P(OPh)
3 + 3 HCl
where "Ph" stands for the
phenyl
In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...
group, -C
6H
5.
Alcohols such as ethanol react similarly in the presence of a
base such as a tertiary amine:
:PCl
3 + 3 EtOH + 3 R
3N → P(OEt)
3 + 3 R
3NH
+Cl
−
In the absence of base, however, the reaction proceeds with the following stoichiometry to give
diethylphosphite:
:PCl
3 + 3 EtOH → (EtO)
2P(O)H + 2 HCl + EtCl
Secondary
amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen
Hydrogen is the chemical element wi ...
s (R
2NH) form
aminophosphines. For example,
bis(diethylamino)chlorophosphine
Bis(diethylamino)chlorophosphine is an organophosphorus compound with the formula (Et2N)2PCl (Et = ethyl). A colorless liquid, it serves as a masked source of PCl2+.
Synthesis and reactions
The compound is prepared by treatment of phosphorus tr ...
, (Et
2N)
2PCl, is obtained from
diethylamine
Diethylamine is an organic compound with the formula (CH3CH2)2NH. It is a secondary amine. It is a flammable, weakly alkaline liquid that is miscible with most solvents. It is a colorless liquid, but commercial samples often appear brown due to im ...
and PCl
3.
Thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
s (RSH) form P(SR)
3. An industrially relevant reaction of PCl
3 with amines is phosphonomethylation, which employs
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
:
: R
2NH + PCl
3 + CH
2O → (HO)
2P(O)CH
2NR
2 + 3 HCl
Aminophosphonates are widely used as sequestering and antiscale agents in water treatment. The large volume herbicide
glyphosate
Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshik ...
is also produced this way. The reaction of PCl
3 with
Grignard reagents and
organolithium reagent
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...
s is a useful method for the preparation of organic
phosphine
Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
s with the formula R
3P (sometimes called phosphanes) such as
triphenylphosphine
Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...
, Ph
3P.
:3 PhMgBr + PCl
3 → Ph
3P + 3 MgBrCl
Under controlled conditions or especially with bulky organic groups, similar reactions afford less substituted derivatives such as
chlorodiisopropylphosphine.
PCl3 as a nucleophile
Phosphorus trichloride has a lone pair, and therefore can act as a
Lewis base, e.g., forming a 1:1 adduct Br
3B-PCl
3. Metal complexes such as Ni(PCl
3)
4 are known, again demonstrating the ligand properties of PCl
3.
This Lewis basicity is exploited in the
Kinnear–Perren reaction to prepare alkylphosphonyl dichlorides (RP(O)Cl
2) and alkyl
phosphonate
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly ...
esters (RP(O)(OR')
2). Alkylation of phosphorus trichloride is effected in the presence of
aluminium trichloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often conta ...
give the alkyltrichlorophosphonium salts, which are versatile intermediates:
:PCl
3 + RCl + AlCl
3 → RPCl + AlCl
The RPCl product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl
2.
PCl3 as a ligand
PCl
3, like the more popular
phosphorus trifluoride
Phosphorus trifluoride (formula P F3), is a colorless and odorless gas. It is highly toxic and reacts slowly with water. Its main use is as a ligand in metal complexes. As a ligand, it parallels carbon monoxide in metal carbonyls, and indeed ...
, is a ligand in
coordination chemistry. One example is Mo(CO)
5PCl
3.
Uses
PCl
3 is important indirectly as a precursor to
PCl5,
POCl3 and
PSCl3, which are used in many applications, including
herbicides,
insecticides,
plasticiser
A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture.
Plasticize ...
s,
oil additives, and
flame retardant
The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...
s.
For example, oxidation of PCl
3 gives
POCl3, which is used for the manufacture of
triphenyl phosphate
Triphenyl phosphate (TPhP) is the chemical compound with the formula OP(OC6H5)3. This colourless solid is the ester (triester) of phosphoric acid and phenol. It is used as a plasticizer and a fire retardant in a wide variety of settings and produc ...
and
tricresyl phosphate
Tricresyl phosphate (TCP), is a mixture of three isomeric organophosphate compounds most notably used as a flame retardant and as a plasticizer in manufacturing for lacquers and varnishes and vinyl plastics. Pure tricresyl phosphate is a colourles ...
, which find application as
flame retardant
The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...
s and
plasticiser
A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture.
Plasticize ...
s for
PVC. They are also used to make
insecticides such as
diazinon
Diazinon (IUPAC name: ''O'',''O''-Diethyl ''O''- -methyl-6-(propan-2-yl)pyrimidin-2-ylphosphorothioate, INN - Dimpylate), a colorless to dark brown liquid, is a thiophosphoric acid ester developed in 1952 by Ciba-Geigy, a Swiss chemical company ...
. Phosphonates include the
herbicide glyphosate
Glyphosate (IUPAC name: ''N''-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshik ...
.
PCl
3 is the precursor to
triphenylphosphine
Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...
for the
Wittig reaction
The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Mos ...
, and
phosphite ester
The general structure of a phosphite ester showing the lone pairs on the P
In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of a ...
s which may be used as industrial intermediates, or used in the
Horner-Wadsworth-Emmons reaction, both important methods for making
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s. 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
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...
generally gives better yields than PCl
3.
Safety
* 600
ppm is lethal in just a few minutes.
* 25 ppm is the US
NIOSH "
Immediately Dangerous to Life and Health" level
* 0.5 ppm is the US
OSHA
OSHA or Osha may refer to:
Work
* Occupational Safety and Health Administration, a federal agency of the United States that regulates workplace safety and health
* Occupational Safety and Health Act (United States) of 1970, a federal law in the Un ...
"
permissible exposure limit
The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupational ...
" over a time-weighted average of 8 hours.
* 0.2 ppm is the US
NIOSH "
recommended exposure limit
A recommended exposure limit (REL) is an occupational exposure limit that has been recommended by the United States National Institute for Occupational Safety and Health. The REL is a level that NIOSH believes would be protective of worker safet ...
" over a time-weighted average of 8 hours.
* Under
EU Directive 67/548/EEC
The Dangerous Substances Directive (as amended) was one of the main European Union laws concerning chemical safety, until its full replacement by the new regulation CLP Regulation (2008), starting in 2016. It was made under Article 100 (Art. 94 ...
, PCl
3 is classified as
''very toxic'' and ''
corrosive
A corrosive substance is one that will damage or destroy other substances with which it comes into contact by means of a chemical reaction.
Etymology
The word ''corrosive'' is derived from the Latin verb ''corrodere'', which means ''to gnaw'', ...
'' , and the
risk phrases R14, R26/28, R35 and R48/20 are obligatory.
Industrial production of phosphorus trichloride is controlled under the
Chemical Weapons Convention, where it is listed in
schedule 3, as it can be used to produce
mustard agents.
See also
*
Phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...
*
Phosphoryl chloride
Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phos ...
*
Phosphorus trifluorodichloride
References
{{Chemical agents
Inorganic phosphorus compounds
Phosphorus chlorides
Phosphorus(III) compounds
Pulmonary agents