Phosphoryl chloride

Phosphoryl chloride
Names
	Preferred IUPAC name Phosphoryl trichloride
	Other names Phosphorus(V) oxychloride; Phosphoric trichloride; Trichlorophosphate; Phosphorus(V) oxide trichloride;
Identifiers
CAS Number	10025-87-3 ;
3D model (JSmol)	Interactive image ; Interactive image ;
ChEBI	CHEBI:30336 ;
ChemSpider	23198 ;
ECHA InfoCard	100.030.030
EC Number	233-046-7;
Gmelin Reference	2272
PubChem CID	24813 ;
RTECS number	TH4897000;
UNII	9XM78OL22K ;
UN number	1810
CompTox Dashboard (EPA)	DTXSID5029710 ;
	InChI InChI=1S/Cl3OP/c1-5(2,3)4 Key: XHXFXVLFKHQFAL-UHFFFAOYSA-N ; InChI=1/Cl3OP/c1-5(2,3)4 Key: XHXFXVLFKHQFAL-UHFFFAOYAS;
	SMILES O=P(Cl)(Cl)Cl; [O-][P+](Cl)(Cl)Cl;
Properties
Chemical formula	POCl3
Molar mass	153.32 g·mol−1
Appearance	colourless liquid, fumes in moist air
Odor	pungent and musty
Density	1.645 g/cm3, liquid
Melting point	1.25 °C (34.25 °F; 274.40 K)
Boiling point	105.8 °C (222.4 °F; 378.9 K)
Solubility in water	Reacts
Solubility	highly soluble in benzene, chloroform, carbon disulfide, carbon tetrachloride
Vapor pressure	40 mmHg (27 °C)
Refractive index (nD)	1.460
Structure
Molecular shape	Tetrahedral at the P atom
Dipole moment	2.54 D
Thermochemistry
Heat capacity (C)	138.8 J·mol−1·K−1 (liquid), 84.9 J·mol−1·K−1 (gas)
Std molar; entropy (S⦵298)	222.5 J·mol−1·K−1 (liquid), 325.5 J·mol−1·K−1 (gas)
Std enthalpy of; formation (ΔfH⦵298)	−597.1 kJ·mol−1 (liquid), −558.5 kJ·mol−1 (gas)
Gibbs free energy (ΔfG⦵)	−520.8 kJ·mol−1 (liquid), −512.9 kJ·mol−1(gas)
Enthalpy of fusion (ΔfH⦵fus)	13.1 kJ·mol−1
Enthalpy of vaporization (ΔfHvap)	38.6 kJ·mol−1
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Toxic and corrosive; releases HCl on contact with water
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H314, H330, H372
Precautionary statements	P260, P264, P270, P271, P280, P284, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P314, P320, P321, P330, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 2 W
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	380 mg/kg (rat, oral)
	NIOSH (US health exposure limits):
PEL (Permissible)	none
REL (Recommended)	TWA 0.1 ppm (0.6 mg/m3) ST 0.5 ppm (3 mg/m3)
IDLH (Immediate danger)	N.D.
Safety data sheet (SDS)	ICSC 0190
Related compounds
Related compounds	Thiophosphoryl chloride ; Phosphorus oxybromide ; Phosphorus trichloride ; Phosphorus pentachloride ;
Supplementary data page
	Phosphoryl chloride (data page)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Last updated March 05, 2024

Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula P O Cl ₃. It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosphorus trichloride and oxygen or phosphorus pentoxide.^[4] It is mainly used to make phosphate esters.

Structure

Unit cell of phosphoryl chloride. Phosphoryl-chloride-unit-cell-down-c-axis-3D-bs-17.png — Unit cell of phosphoryl chloride.

Like phosphate, POCl₃ is tetrahedral in shape.^[6] It features three P−Cl bonds and one strong P–O bond, with an estimated bond dissociation energy of 533.5 kJ/mol. Unlike in the case of POF₃, the Schomaker-Stevenson rule predicts appropriate bond length for the P–O bond only if the P–O bond is treated as a double bond, P=O.^{[ citation needed ]} More modern treatments explain the tight P–O bond as a combination of lone pair transfer from the phosphorus to the oxygen atom and a dative π back-bond that produces an effective [P⁺]-[O⁻] configuration.^[7]

Phosphoryl chloride exists as neutral POCl₃ molecules in the solid, liquid and gas states. This is unlike phosphorus pentachloride which exists as neutral PCl₅ molecules in the gas and liquid states but adopts the ionic form [PCl₄]⁺[PCl₆]⁻ (tetrachlorophosphonium hexachlorophosphate(V)) in the solid state. The average bond lengths in the crystal structure of POCl₃ are 1.98 Å for P–Cl and 1.46 Å for P=O.^[5]

Physical properties

It has a critical pressure of 3.4 atm.^[8] With a freezing point of 1 °C and boiling point of 106 °C, the liquid range of POCl₃ is rather similar to water. Also like water, POCl₃ autoionizes, owing to the reversible formation of [POCl₂]⁺ cations (dichlorooxophosphonium cations) and Cl⁻ anions.

Chemical properties

POCl₃ reacts with water to give hydrogen chloride and phosphoric acid:

O=PCl₃ + 3 H₂O → O=P(OH)₃ + 3 HCl

Intermediates in the conversion have been isolated, including pyrophosphoryl chloride, O(−P(=O)Cl₂)₂.^[9]

Upon treatment with excess alcohols and phenols, POCl₃ gives phosphate esters:

O=PCl₃ + 3 ROH → O=P(OR)₃ + 3 HCl

Such reactions are often performed in the presence of an HCl acceptor such as pyridine or an amine.

POCl₃ can also act as a Lewis base, forming adducts with a variety of Lewis acids such as titanium tetrachloride:

POCl₃ + TiCl₄ → POCl₃·TiCl₄

The aluminium chloride adduct (POCl₃·AlCl₃) is quite stable, and so POCl₃ can be used to remove AlCl₃ from reaction mixtures, for example at the end of a Friedel-Crafts reaction.

POCl₃ reacts with hydrogen bromide in the presence of Lewis-acidic catalysts to produce POBr₃.

Preparation

Phosphoryl chloride can be prepared by many methods. Phosphoryl chloride was first reported in 1847 by the French chemist Adolphe Wurtz by reacting phosphorus pentachloride with water.^[10]

By oxidation

The commercial method involves oxidation of phosphorus trichloride with oxygen:^[11]

2 PCl₃ + O₂ → 2 POCl₃

An alternative method involves the oxidation of phosphorus trichloride with potassium chlorate:^[12]

3 PCl₃ + KClO₃ → 3 POCl₃ + KCl

Oxygenations

The reaction of phosphorus pentachloride (PCl₅) with phosphorus pentoxide (P₄O₁₀).

6 PCl₅ + P₄O₁₀ → 10 POCl₃

The reaction can be simplified by chlorinating a mixture of PCl₃ and P₄O₁₀, generating the PCl₅ in situ. The reaction of phosphorus pentachloride with boric acid or oxalic acid:^[12]

3 PCl₅ + 2 B(OH)₃ → 3 POCl₃ + B₂O₃ + 6 HCl

PCl₅ + (COOH)₂ → POCl₃ + CO + CO₂ + 2 HCl

Other methods

Reduction of tricalcium phosphate with carbon in the presence of chlorine gas:^[13]

Ca₃(PO₄)₂ + 6 C + 6 Cl₂ → 3 CaCl₂ + 6 CO + 2 POCl₃

The reaction of phosphorus pentoxide with sodium chloride is also reported:^[13]

2 P₂O₅ + 3 NaCl → 3 NaPO₃ + POCl₃

Uses

Phosphoryl chloride is used on an industrial scale for the manufacture of phosphate esters (organophosphates). These have a wide range of uses, including as flame retardants (bisphenol A diphenyl phosphate, TCPP and tricresyl phosphate), plasticisers for PVC and related polymers ( 2-ethylhexyl diphenyl phosphate) and hydraulic fluids.^[11] POCl₃ is also used in the production of organophosphate insecticides.

In the semiconductor industry, POCl₃ is used as a safe liquid phosphorus source in diffusion processes. The phosphorus acts as a dopant used to create n-type layers on a silicon wafer.

As a reagent

In the laboratory, POCl₃ is a reagent in dehydrations. One example involves conversion of formamides to isonitriles (isocyanides);^[14] primary amides to nitriles:^[15]

RC(O)NH₂ + POCl₃ → RCN + P(O)OHCl + 2 HCl

In a related reaction, certain aryl-substituted amides can be cyclized using the Bischler-Napieralski reaction.

Such reactions are believed to proceed via an imidoyl chloride. In certain cases, the imidoyl chloride is the final product. For example, pyridones and pyrimidones can be converted to chloro- derivatives such as 2-chloropyridines and 2-chloropyrimidines, which are intermediates in the pharmaceutical industry.^[16]

In the Vilsmeier-Haack reaction, POCl₃ reacts with amides to produce a "Vilsmeier reagent", a chloro-iminium salt, which subsequently reacts with electron-rich aromatic compounds to produce aromatic aldehydes upon aqueous work-up.^[17]

Related Research Articles

Phosphorus is a chemical element; it has 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 Earth. It has a concentration in the Earth's crust of about one gram per kilogram. In minerals, phosphorus generally occurs as phosphate.

In organic chemistry, an acyl chloride is an organic compound with the functional group −C(=O)Cl. Their formula is usually written R−COCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH₃COCl. Acyl chlorides are the most important subset of acyl halides.

Organochlorine chemistry is concerned with the properties of organochlorine compounds, or organochlorides, organic compounds containing at least one covalently bonded atom of chlorine. The chloroalkane class includes common examples. The wide structural variety and divergent chemical properties of organochlorides lead to a broad range of names, applications, and properties. Organochlorine compounds have wide use in many applications, though some are of profound environmental concern, with TCDD being one of the most notorious.

<span class="mw-page-title-main">Acetyl chloride</span> Organic compound (CH₃COCl)

Acetyl chloride is an acyl chloride derived from acetic acid. It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl.

<span class="mw-page-title-main">Thionyl chloride</span> Inorganic compound (SOCl2)

Thionyl chloride is an inorganic compound with the chemical formula SOCl₂. It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes per year being produced during the early 1990s, but is occasionally also used as a solvent. It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons.

Phosphorus pentachloride is the chemical compound with the formula PCl₅. It is one of the most important phosphorus chlorides/oxychlorides, others being PCl₃ and POCl₃. PCl₅ finds use as a chlorinating reagent. It is a colourless, water-sensitive solid, although commercial samples can be yellowish and contaminated with hydrogen chloride.

<span class="mw-page-title-main">Phosphorus trichloride</span> Chemical compound

Phosphorus trichloride is an inorganic compound with the chemical formula PCl₃. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic and reacts readily with water to release hydrogen chloride.

Tributyl phosphate, known commonly as TBP, is an organophosphorus compound with the chemical formula (CH₃CH₂CH₂CH₂O)₃PO. This colourless, odorless liquid finds some applications as an extractant and a plasticizer. It is an ester of phosphoric acid with n-butanol.

<span class="mw-page-title-main">Tantalum(V) chloride</span> Chemical compound

Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl₅. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl₃) and eventually tantalum pentoxide (Ta₂O₅); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.

<span class="mw-page-title-main">Phosphite ester</span> Organic compound with the formula P(OR)3

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 an unobserved tautomer phosphorous acid, H₃PO₃, with the simplest example being trimethylphosphite, P(OCH₃)₃. Some phosphites can be considered esters of the dominant tautomer of phosphorous acid (HP(O)(OH)₂). The simplest representative is dimethylphosphite with the formula HP(O)(OCH₃)₂. Both classes of phosphites are usually colorless liquids.

Vanadium oxytrichloride is the inorganic compound with the formula VOCl₃. This yellow distillable liquid hydrolyzes readily in air. It is an oxidizing agent. It is used as a reagent in organic synthesis. Samples often appear red or orange owing to an impurity of vanadium tetrachloride.

<span class="mw-page-title-main">Antimony pentachloride</span> Chemical compound

Antimony pentachloride is a chemical compound with the formula SbCl₅. It is a colourless oil, but typical samples are yellowish due to dissolved chlorine. Owing to its tendency to hydrolyse to hydrochloric acid, SbCl₅ is a highly corrosive substance and must be stored in glass or PTFE containers.

<span class="mw-page-title-main">Arsenic trichloride</span> Chemical compound

Arsenic trichloride is an inorganic compound with the formula AsCl₃, also known as arsenous chloride or butter of arsenic. This poisonous oil is colourless, although impure samples may appear yellow. It is an intermediate in the manufacture of organoarsenic compounds.

<span class="mw-page-title-main">Phosphorus trioxide</span> Chemical compound

Phosphorus trioxide is the chemical compound with the molecular formula P₄O₆. Although the molecular formula suggests the name tetraphosphorus hexoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, and its usage continues today. This colorless solid is structurally related to adamantane. It is formally the anhydride of phosphorous acid, H₃PO₃, but cannot be obtained by the dehydration of the acid. A white solid that melts at room temperature, it is waxy, crystalline and highly toxic, with garlic odor.

<span class="mw-page-title-main">Hexachlorophosphazene</span> Chemical compound

Hexachlorophosphazene is an inorganic compound with the formula (NPCl₂)₃. The molecule has a cyclic, unsaturated backbone consisting of alternating phosphorus and nitrogen centers, and can be viewed as a trimer of the hypothetical compound N≡PCl₂. Its classification as a phosphazene highlights its relationship to benzene. There is large academic interest in the compound relating to the phosphorus-nitrogen bonding and phosphorus reactivity.

<span class="mw-page-title-main">Thiophosphoryl chloride</span> Chemical compound

Thiophosphoryl chloride is an inorganic compound with the chemical formula PSCl₃. It is a colorless pungent smelling liquid that fumes in air. It is synthesized from phosphorus chloride and used to thiophosphorylate organic compounds, such as to produce insecticides.

In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula AO_mX_n, where X is a halogen. Known oxohalides have fluorine (F), chlorine (Cl), bromine (Br), and/or iodine (I) in their molecules. The element A may be a main group element, a transition element, a rare earth element or an actinide. The term oxohalide, or oxyhalide, may also refer to minerals and other crystalline substances with the same overall chemical formula, but having an ionic structure.

Difluorophosphate or difluorodioxophosphate or phosphorodifluoridate is an anion with formula PO₂F−2. It has a single negative charge and resembles perchlorate and monofluorosulfonate in shape and compounds. These ions are isoelectronic, along with tetrafluoroaluminate, phosphate, orthosilicate, and sulfate. It forms a series of compounds. The ion is toxic to mammals as it causes blockage to iodine uptake in the thyroid. However it is degraded in the body over several hours.

Phosphoric chloride difluoride POF₂Cl is a colourless gas. At one atmosphere pressure the gas condenses to a liquid at 3.1°C and freezes at −96.4. Alternate names are difluorophosphoryl chloride or phosphoryl chloride difluoride.

<span class="mw-page-title-main">Isocyanide dichloride</span>

Isocyanide dichlorides are organic compounds containing the RN=CCl₂ functional group. Classically they are obtained by chlorination of isocyanides. Phenylcarbylamine chloride is a well-characterized example.

References

↑ Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 926. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
1 2 3 4 5 NIOSH Pocket Guide to Chemical Hazards. "#0508". National Institute for Occupational Safety and Health (NIOSH).
↑ CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data. William M. Haynes, David R. Lide, Thomas J. Bruno (2016-2017, 97th ed.). Boca Raton, Florida. 2016. ISBN 978-1-4987-5428-6. OCLC 930681942.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: others (link)
↑ Toy, Arthur D. F. (1973). The Chemistry of Phosphorus. Oxford: Pergamon Press. ISBN 978-0-08-018780-8. OCLC 152398514.
1 2 Olie, K. (1971). "The crystal structure of POCl₃". Acta Crystallogr. B . 27 (7): 1459–1460. doi:10.1107/S0567740871004138.
↑ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann.
↑ Chesnut, D. B.; Savin, A. (1999). "The Electron Localization Function (ELF) Description of the PO Bond in Phosphine Oxide". Journal of the American Chemical Society . 121 (10): 2335–2336. doi:10.1021/ja984314m. ISSN 0002-7863.
↑ "Phosphoryl chloride".
↑ Grunze, Herbert (1963). "Über die Hydratationsprodukte des Phosphoroxychlorides. III. Darstellung von Pyrophosphorylchlorid aus partiell hydrolysiertem Phosphoroxychlorid (Hydration products of phosphorus oxychloride. III. Preparation of pyrophosphoryl chloride from partially hydrolyzed phosphorus oxychloride)". Zeitschrift für Anorganische und Allgemeine Chemie. 324: 1–14. doi:10.1002/zaac.19633240102.
↑ Wurtz, Adolphe (1847). "Sur l'acide sulfophosphorique et le chloroxyde de phosphore" [On monothiophosphoric acid and phosphoryl chloride]. Annales de Chimie et de Physique. 3rd series (in French). 20: 472–481.; see Chloroxyde de phosphore, pp. 477–481. (Note: Wurtz's empirical formulas are wrong because, like many chemists of his day, he used the wrong atomic mass for oxygen.)Roscoe, Henry Enfield; Schorlemmer, Carl; Cannell, John, eds. (1920). A Treatise on Chemistry. Vol. 1 (5th ed.). London, England: Macmillan and Co. p. 676.
1 2 Bettermann, Gerhard; Krause, Werner; Riess, Gerhard; Hofmann, Thomas (2000). "Phosphorus Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_527. ISBN 978-3527306732..
1 2 Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. New York: McGraw-Hill. p. 709. ISBN 0-07-049439-8.
1 2 Lerner, Leonid (2011). Small-Scale Synthesis of Laboratory Reagents with Reaction Modeling. Boca Raton, Florida: CRC Press. pp. 169–177. ISBN 978-1-4398-1312-6.
↑ Patil, Pravin; Ahmadian-Moghaddam, Maryam; Dömling, Alexander (29 September 2020). "Isocyanide 2.0". Green Chemistry. 22 (20): 6902–6911. doi: 10.1039/D0GC02722G .
↑ March, J. (1992). Advanced Organic Chemistry (4th ed.). New York, NY: Wiley. p. 723. ISBN 978-0-471-60180-7.
↑ Elderfield, R. C. (ed.). Heterocyclic Compound. Vol. 6. New York, NY: John Wiley & Sons. p. 265.
↑ Hurd, Charles D.; Webb, Carl N. (1925). "p-Dimethylaminobenzophenone". Organic Syntheses. 7: 24. doi:10.15227/orgsyn.007.0024.