Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Pyrophosphoric acid: Difference between pages

| Watchedfields = changed

| verifiedrevid = 477001359

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| ImageName = Chemical structure of pyrophosphoric acid

| ImageFile1 = Pyrophosphoric-acid-3D-vdW.png

| ImageName1 = 3D model of pyrophosphoric acid

| IUPACName = Diphosphoric acid<br />μ-oxido-bis(dihydroxidooxidophosphorus)

| OtherNames = Pyrophosphoric acid<br/>Phosphonophosphoric acid<br/>Phosphono dihydrogenphosphate

|Section1={{Chembox Identifiers

| IUPHAR_ligand = 3151

| ChEBI_Ref = {{ebicite|correct|EBI}}

| PubChem = 1023

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|Section2={{Chembox Properties

| Formula = H₄P₂O₇

| MolarMass = 177.97 g/mol

| Density =

| MeltingPtC = 71.5

| BoilingPt =

| Solubility = Extremely soluble

| SolubleOther = Very soluble in [[ethanol|alcohol]], [[diethyl ether|ether]]

| ConjugateBase = [[Pyrophosphate]]

'''Pyrophosphoric acid''', also known as '''diphosphoric acid''', is the inorganic compound with the formula H₄P₂O₇ or, more descriptively, [(HO)₂P(O)]₂O. Colorless and odorless, it is soluble in [[water (molecule)|water]], [[diethyl ether]], and [[ethyl alcohol]]. The anhydrous acid crystallizes in two [[Polymorphism (materials science)|polymorph]]s, which melt at 54.3 and 71.5&nbsp;°C. The compound is a component of polyphosphoric acid, an important source of phosphoric acid.<ref name=Ullmann/> [[Anion]]s, [[salt (chemistry)|salt]]s, and [[ester]]s of pyrophosphoric acid are called [[pyrophosphate]]s.

==Preparation==

It can be prepared by reaction of phosphoric acid with [[phosphoryl chloride]]:<ref>{{cite book|author1=R. Klement|chapter=Condensed Orthophosphates|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY, NY|volume=2|pages=546}}</ref>

:{{chem2|5 H3PO4 + POCl3}} → {{chem2|3 H4P2O7 + 3 HCl}}

It can also be prepared by ion exchange from sodium pyrophosphate or by treating lead pyrophosphate with [[hydrogen sulfide]].<ref name=Ullmann>{{cite book |doi=10.1002/14356007.a19_465.pub4|chapter=Phosphoric Acid and Phosphates |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2022 |last1=Havelange |first1=Sébastien |last2=Lierde |first2=Nicolas |last3=Germeau |first3=Alain |last4=Martins |first4=Emmanuel |last5=Theys |first5=Tibaut |last6=Sonveaux |first6=Marc |last7=Toussaint |first7=Claudia |last8=Schrödter |first8=Klaus |last9=Bettermann |first9=Gerhard |last10=Staffel |first10=Thomas |last11=Wahl |first11=Friedrich |last12=Klein |first12=Thomas |last13=Hofmann |first13=Thomas |pages=1–55 |isbn=9783527303854 |s2cid=246266565 }}</ref>

Boiling the water from [[orthophosphoric acid]] will not dehydrate it to pure pyrophosphoric acid, instead a mixture of ortho, pyro, and [[polyphosphoric acid]]s are produced, the maximum pyrophosphoric acid concentration remains below 50% and occurs slightly before what would otherwise be pure pyrophosphoric acid.<ref>{{Citation |last=Korte |first=Carsten |title=Phosphoric Acid and its Interactions with Polybenzimidazole-Type Polymers |date=2016 |url=http://link.springer.com/10.1007/978-3-319-17082-4_8 |work=High Temperature Polymer Electrolyte Membrane Fuel Cells |pages=169–194 |editor-last=Li |editor-first=Qingfeng |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-17082-4_8 |isbn=978-3-319-17081-7 |access-date=2023-02-11 |last2=Conti |first2=Fosca |last3=Wackerl |first3=Jürgen |last4=Lehnert |first4=Werner |editor2-last=Aili |editor2-first=David |editor3-last=Hjuler |editor3-first=Hans Aage |editor4-last=Jensen |editor4-first=Jens Oluf}}</ref>

==Reactions==

Pyrophosphoric acid is a tetraprotic acid, with four distinct pKa's:<ref>{{cite journal |doi=10.1039/d1qi00209k|title=Induced fit activity-based sensing: A mechanistic study of pyrophosphate detection with a "flexible" Fe-salen complex |year=2021 |last1=Yadav |first1=Prerna |last2=Blacque |first2=Olivier |last3=Roodt |first3=Andreas |last4=Zelder |first4=Felix |journal=Inorganic Chemistry Frontiers |volume=8 |issue=19 |pages=4313–4323 |pmid=34603734 |pmc=8477187 }}</ref>

:{{chem2|H4P2O7 <-> [H3P2O7]- + H+}}, pKa = 0.85

:{{chem2|[H3P2O7]- <-> [H2P2O7](2-) + H+}}, pKa = 1.96

:{{chem2|[H2P2O7](2-) <-> [HP2O7](3-) + H+}}, pKa = 6.60

:{{chem2|[HP2O7](3-) <-> [P2O7](4-) + H+}}, pKa = 9.41

The pKa's occur in two distinct ranges because deprotonations occur on separate phosphate groups. For comparison with the pKa's for [[phosphoric acid]] are 2.14, 7.20, and 12.37.

At physiological pH's, pyrophosphate exists as a mixture of doubly and singly protonated forms.

When molten, pyrophosphoric acid rapidly converts to an equilibrium mixture of phosphoric acid, pyrophosphoric acid and polyphosphoric acids. The percentage by weight of pyrophosphoric acid is around 40% and it is difficult to recrystallise from the melt.

Even in cold water, pyrophosphoric acid hydrolyses to phosphoric acid. All polyphosphoric acids behave similarly.<ref name="StudiesinInorganicvol20">{{cite book |last=Corbridge |first=D. |title=Studies in inorganic Chemistry vol. 20|publisher=Elsevier Science B.V. |date=1995 |pages=169–305 |chapter=Chapter 3: Phosphates |isbn=0-444-89307-5|doi=10.1016/B978-0-444-89307-9.50008-8}}</ref>

:{{chem2|H4P2O7 + H2O -> 2 H3PO4}}

==Safety==

While pyrophosphoric acid is corrosive, it is not known to be otherwise toxic.<ref>[http://www.sciencelab.com/msds.php?msdsId=9924773 Material Safety Data Sheet: Pyrophosphoric acid MSDS] ''www.sciencelab.com''</ref>

==History==

The name pyrophosphoric acid was given by a "Mr. Clarke of Glasgow" in 1827 who is credited with its discovery following the heating to red heat of a [[Sodium phosphates|sodium phosphate]] salt. It was found that phosphoric acid when heated to red heat formed pyrophosphoric acid that was readily converted to phosphoric acid by hot water.<ref>{{cite book |last=Beck |first=Lewis Caleb |title=A Manual of Chemistry: Containing a Condensed View of the Present State of the Science, with Copious References to More Extensive Treatises, Original Papers, Etc|publisher=E.W & C Skinner |date=1834 |pages=160 |url=https://books.google.com/books?id=wlE6AQAAMAAJ&q=A+Manual+of+Chemistry%3A+Containing+a+Condensed+View+of+the+Present+State|access-date=January 30, 2015}}</ref>

==See also==

* [[Disulfuric acid]]

* [[Sodium pyrophosphate]]

* [[Calcium pyrophosphate dihydrate deposition disease]]

* [[Dimethylallyl pyrophosphate]]

* [[Adenosine diphosphate|ADP]]

* [[Adenosine triphosphate|ATP]]

* [[Ortho acid]]s

* [[triphosphoric acid]]

==References==

<references/>

==External links==

*[https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=217793 Pyrophosphoric acid at PubChem]

{{Hydrogen compounds}}

[[Category:Hydrogen compounds]]

[[Category:Pyrophosphates]]

[[Category:Phosphorus oxoacids]]

[[Category:Acid anhydrides]]

[[Category:Phosphorus(V) compounds]]