pyrophosphoryl chloride
{{Chembox
| ImageFile = P2O3Cl4.svg
| ImageSize =
| ImageAlt =
| IUPACName =
| OtherNames = Diphosphoryl tetrachloride
|Section1={{Chembox Identifiers
| CASNo = 13498-14-1
| CASNo_Ref = {{Cascite|correct|CAS}}
| ChemSpiderID = 3632294
| EC_number = 236-824-4
| PubChem = 4432411
| StdInChI=1S/Cl4O3P2/c1-8(2,5)7-9(3,4)6
| StdInChIKey = CNTIXUGILVWVHR-UHFFFAOYSA-N
| SMILES = O=P(OP(=O)(Cl)Cl)(Cl)Cl
}}
|Section2={{Chembox Properties
| Formula = {{chem2|O(POCl2)2}}
| P = 2|Cl=4|O=3
| MolarMass =
| Appearance = colorless liquid
| Density = 1.74 g/cm3
| MeltingPt =
| MeltingPt_notes =
| BoilingPtC = 66-68
| BoilingPt_notes = 0.01 Torr
| Solubility = }}
|Section3={{Chembox Hazards
| GHS_ref=[https://pubchem.ncbi.nlm.nih.gov/compound/4432411#section=Safety-and-Hazards]
| GHSPictograms = {{GHS05}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|314}}
| PPhrases = {{P-phrases|260|264|280|301+330+331|302+361+354|304+340|305+354+338|316|321|363|405|501}}
| MainHazards =
}}
}}
Pyrophosphoryl chloride is the inorganic compound with the formula {{chem2|P2O3Cl4|auto=1}}. Its structure is {{chem2|O(POCl2)2}}. It is a colorless syrup. In terms of its chemical structure, the compound consists of two tetrahedral phosphorus sites that share an oxo bridge. The name implies that the compound is a derivative of pyrophosphoric acid, {{chem2|O(PO(OH)2)2}}.
The compound is obtained by treating phosphoryl chloride with half an equivalent of methanol, as described in the following chemical equation:{{cite journal |doi=10.1055/s-1992-21272 |date=1992 |issue=1 |last1=Cheung |first1=Gi K. |last2=Downie |first2=Ian M. |last3=Earle |first3=Martyn J. |last4=Heaney |first4=Harry |last5=Matough |first5=M. Fathy S. |last6=Shuhaibar |first6=Khamis F. |last7=Thomas |first7=Deborah |title=A Convenient Preparation of Pyrophosphoryl Chloride and Its Use in Vilsmeier Formylation Reactions |journal=Synlett}}
:{{chem2|2 POCl3 + CH3OH -> O(POCl2)2 + CH3Cl + HCl}}
Pyrophosphoryl chloride is proposed as an intermediate in the chlorination of alcohols by phosphoryl chloride. It is also a reagent for Vilsmeier-Haack formylations.{{cite journal |doi=10.1016/s0040-4020(01)89915-4 |date=1993 |volume=49 |issue=19 |last1=Downie |first1=Ian M. |last2=Earle |first2=Martyn J. |last3=Heaney |first3=Harry |last4=Shuhaibar |first4=Khamis F. |title=Vilsmeier formylation and glyoxylation reactions of nucleophilic aromatic compounds using pyrophosphoryl chloride |journal=Tetrahedron}}