Phosphorus trichloride is a
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of
phosphorusPhosphorus 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...
and
chlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, having
chemical formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
PCl
3. Its shape is trigonal pyramidal. It is the most important of the three
phosphorus chloridesPhosphorus 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 an important
industrial chemicalThe chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials into more than 70,000 different products.-Products:...
, being used for the manufacture of organophosphorus compounds for a wide variety of applications. It has a
31P NMR signal at around +220 ppm.
Chemical properties
The
phosphorusPhosphorus 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 PCl
3 is often considered to have the +3
oxidation stateIn 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...
and the
chlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
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 compounds, undergoing
oxidationRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
to phosphorus pentachloride (PCl
5),
thiophosphoryl chlorideThiophosphoryl chloride is an inorganic compound with the formula PSCl3. Thiophosphoryl chloride, PSCl3, is a fuming, colorless liquid with a pungent odor...
(PSCl
3), or phosphorus oxychloride (POCl
3).
If an
electric dischargeElectrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...
is passed through a mixture of PCl
3 vapour and
hydrogenHydrogen 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, a rare chloride of phosphorus is formed, diphosphorus tetrachloride (P
2Cl
4).
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 rapidly and
exothermicIn thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...
ally with water to form
phosphorous acidPhosphorous acid is the compound described by the formula H3PO3. This acid is diprotic , not triprotic as might be suggested by this formula. Phosphorous acid is as an intermediate in the preparation of other phosphorus compounds.-Nomenclature and tautomerism:H3PO3 is more clearly described with...
, H
3PO
3 and
HClHydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
:
- PCl3 + 3 H2O → H3PO3 + 3 HCl
A large number of similar substitution reactions are known, the most important of which is the formation of
phosphite esterA phosphite ester or organophosphite is a type of chemical compound with the general structure P3. Phosphite esters can be considered as esters of phosphorous acid, H3PO3. A simple phosphite ester is trimethylphosphite, P3...
s by reaction with
alcoholIn 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 or
phenolsIn organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group...
. For example, with
phenolPhenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
,
triphenyl phosphiteTriphenyl phosphite is the chemical compound with the formula P3. This colourless viscous liquid is the ester of phosphorous acid and phenol. It is used as a ligand in organometallic chemistry...
is formed:
- 3 PhOH + PCl3 → P(OPh)3 + 3 HCl
where "Ph" stands for phenyl group, -C
6H
5.
AlcoholIn 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 such as ethanol react similarly in the presence of a
baseFor the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
such as a tertiary amine:
- PCl3 + 3 EtOH + 3 R3N → P(OEt)3 + 3 R3NH+Cl−
Of the many related compounds can be prepared similarly, triisopropyl phosphite is an example (b.p. 43.5 °C/1.0 mm; CAS# 116-17-6).
In the absence of base, however, the reaction produces phosphonic acid and an alkyl chloride, according to the following stoichiometry:
- PCl3 + 3 C2H5OH → 3 C2H5Cl + H3PO3
Alternatively, under certain conditions the dialkyl
phosphonatePhosphonates or phosphonic acids are organic compounds containing C-PO2 or C-PO2 groups . Bisphosphonates were first synthesized in 1897 by Von Baeyer and Hofmann. An example of such a bisphosphonate is HEDP . Since the work of Schwarzenbach in 1949, phosphonic acids are known as effective...
(dialkyl phosphite) may be isolated, as well as some alkyl chloride:
- PCl3 + 3 iPrOH → iPr2PH=O + iPrCl + 2 HCl(g) where iPr = isopropyl
In organic chemistry, isopropyl is a propyl with a group attached to the secondary carbon. If viewed as a functional group an isopropyl is an organic compound with a propyl group attached at its secondary carbon.The bond is therefore on the middle carbon....
, (CH3)2CH-
AmineAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s, R
2NH, form P(NR
2)
3, and
thiolIn organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
s (RSH) form P(SR)
3. An industrially relevant reaction of PCl
3 with amines is phosphonomethylation, which employs
formaldehydeFormaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
:
- R2NH + PCl3 + CH2O → (HO)2P(O)CH2NR2 + 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 reagentAn organolithium reagent is an organometallic compound with a direct bond between a carbon and a lithium atom. As the electropositive nature of lithium puts most of the charge density of the bond on the carbon atom, effectively creating a carbanion, organolithium compounds are extremely powerful...
s is a useful method for the preparation of organic phosphines with the formula R
3P (sometimes called phosphanes) such as
triphenylphosphineTriphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...
, Ph
3P.
- 3 PhMgBr + PCl3 → Ph3P + 3 MgBrCl
Under controlled conditions PCl
3 can be used to prepare PhPCl
2 and Ph
2PCl.
PCl3 as a nucleophile
Phosphorus trichloride has a lone pair, and therefore can act as a Lewis base, for example with the
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,...
s BBr
3 it forms a 1:1 adduct, Br
3B
−−
+PCl
3. Metal complexes such as Ni(PCl
3)
4 are known. This Lewis basicity is exploited in one useful route to organophosphorus compounds using an alkyl chloride and
aluminium chlorideAluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...
:
- PCl3 + RCl + AlCl3 → RPCl + AlCl
The RPCl 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
tonneThe tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s. Phosphorus trichloride is prepared industrially by the reaction of
chlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
with a
refluxReflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations...
ing solution of white
phosphorusPhosphorus 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 phosphorus trichloride, with continuous removal of PCl
3 as it is formed.
- P4 + 6 Cl2 → 4 PCl3
Industrial production of phosphorus trichloride is controlled under the
Chemical Weapons ConventionThe Chemical Weapons Convention is an arms control agreement which outlaws the production, stockpiling and use of chemical weapons. Its full name is the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction...
, 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,
POCl3Phosphoryl chloride is a colourless liquid with the formula 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...
and
PSCl3Thiophosphoryl chloride is an inorganic compound with the formula PSCl3. Thiophosphoryl chloride, PSCl3, is a fuming, colorless liquid with a pungent odor...
, which in turn enjoy many applications in
herbicideHerbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
s,
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
s, plasticisers,
oil additiveOil additives are chemical compounds that improve the lubricant performance of base oil . By utilizing the same base stock, many different oils can be manufactured, each with its distinctive properties. Additives comprise up to 5% by weight of some oils.Nearly all commercial motor oils contain...
s, and
flame retardantFlame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...
s.
For example oxidation of PCl
3 gives POCl
3, which is used for the manufacture of
triphenyl phosphateTriphenyl phosphate is the chemical compound with the formula OP3. This colourless solid is the ester of phosphoric acid and phenol. It is used as a plasticizer and a fire retardant....
and
tricresyl phosphateTricresyl phosphate, abbreviated TCP, is an organophosphate compound that is used as a plasticizer and diverse other applications. It is a colourless, viscous liquid, although commercial samples are typically yellow...
, which find application as
flame retardantFlame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...
s and plasticisers for
PVCPolyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
. They are also used to make
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
s such as
diazinonDiazinon , a colorless to dark brown liquid, is a thiophosphoric acid ester developed in 1952 by Ciba-Geigy, a Swiss chemical company...
. Phosphonates include the
herbicideHerbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
glyphosate.
PCl
3 is the precursor to
triphenylphosphineTriphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...
for the
Wittig reactionGeorg Wittig was a German chemist who reported a method for synthesis of alkenes from aldehydes and ketones using compounds called phosphonium ylides in the Wittig reaction. He shared the Nobel Prize in Chemistry with Herbert C...
, and
phosphite esterA phosphite ester or organophosphite is a type of chemical compound with the general structure P3. Phosphite esters can be considered as esters of phosphorous acid, H3PO3. A simple phosphite ester is trimethylphosphite, P3...
s which may be used as industrial intermediates, or used in the
Horner-Wadsworth-Emmons reactionThe Horner-Wadsworth-Emmons reaction is the chemical reaction of stabilized phosphonate carbanions with aldehydes to produce predominantly E-alkenes....
, both important methods for making
alkeneIn organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s. It can be used to make
trioctylphosphine oxideTrioctylphosphine oxide is an organophosphorus compound with the formula OP3. Frequently referred to as TOPO, this compound is used as an extraction or stabilizing agent...
(TOPO), used as an extraction agent, although TOPO is usually made via the corresponding phosphine.
PCl
3 is also used directly as a
reagentA reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
in
organic synthesisOrganic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. It is used to convert primary and secondary
alcoholIn 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 into alkyl chlorides, or
carboxylic acidCarboxylic 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 into
acyl chlorideIn organic chemistry, an acyl chloride is an organic compound with the functional group -CO-Cl. Their formula is usually written RCOCl, where R is a side chain. They are usually considered to be reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride,...
s, although
thionyl chlorideThionyl chloride is an inorganic compound with the formula SOCl2. It is a reactive chemical reagent used in chlorination reactions. It is a colorless, distillable liquid at room temperature and pressure that decomposes above 140 °C. Thionyl chloride is sometimes confused with sulfuryl...
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
corrosiveA corrosive substance is one that will destroy or irreversibly damage another surface or substance with which it comes into contact. The main hazards to people include damage to the eyes, the skin, and the tissue under the skin; inhalation or ingestion of a corrosive substance can damage the...
under
EUThe European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
Directive 67/548/EECThe Dangerous Substances Directive is one of the main European Union laws concerning chemical safety. It was made under Article 100 of the Treaty of Rome...
, and the
risk phrases R14, R26/28, R35 and R48/20 are obligatory.