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

|Watchedfields = changed

|verifiedrevid = 470470338

|Reference = <ref name=sigma>[http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/123447 3,4-Dihydroxy-3-cyclobutene-1,2-dione]. [[Sigma-Aldrich]]</ref>

|PIN = 3,4-Dihydroxycyclobut-3-ene-1,2-dione

|OtherNames = Quadratic acid<br/>Cyclobutenedioic acid

|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

|ChemSpiderID = 16919

|EINECS = 220-761-4

|InChI = 1/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H

|InChIKey = PWEBUXCTKOWPCW-UHFFFAOYAC

|StdInChI_Ref = {{stdinchicite|correct|chemspider}}

|StdInChI = 1S/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H

|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

|StdInChIKey = PWEBUXCTKOWPCW-UHFFFAOYSA-N

|CASNo_Ref = {{cascite|correct|CAS}}

|CASNo = 2892-51-5

|UNII_Ref = {{fdacite|correct|FDA}}

|UNII = SVR9D0VODW

|PubChem = 17913

|SMILES = c1(c(c(=O)c1=O)O)O

|C=4 | H=2 | O=4

|Appearance = white crystalline powder

|MeltingPt= >

|MeltingPtC = 300

|pKa = p''K''_a1 = 1.5<br>p''K''_a2 = 3.4

}}

|FlashPtC = 190

|FlashPt_ref = <ref name=alpha>[http://www.alfa.com/en/GP100W.pgm?DSSTK=A15169 3,4-Dihydroxy-3-cyclobutene-1,2-dione, 98+%]. Alfa Aesar</ref>

|Hazards_ref=<ref>{{cite web |title=SICHERHEITSDATENBLATT |url=https://www.merckmillipore.com/INTERSHOP/web/WFS/Merck-DE-Site/de_DE/-/EUR/ShowDocument-File?ProductSKU=MDA_CHEM-803500&DocumentId=803500_SDS_DE_DE.PDF&DocumentType=MSD&Language=DE&Country=DE |date=21 March 2021}}</ref>

|GHSPictograms = {{GHS05}}

|GHSSignalWord = Danger

|HPhrases = {{H-phrases|314}}

|PPhrases = {{P-phrases|P260|P280|P301+P330+P331|P303+P361+P353|P304+P340+P310|P305+P351+P338}}

}}

'''Squaric acid''', also called '''quadratic acid''' because its four carbon atoms approximately form a square, is a [[Polyprotic acids|diprotic]] [[organic acid]] with the [[chemical formula]] {{chem2|C4O2(OH)2}}.<ref name=Westbook>{{cite book|chapter=History of the Oxocarbons|title=Oxocarbons|author=Robert West |editor=Robert West|doi=10.1016/B978-0-12-744580-9.50005-1|year=1980|pages=1–14|publisher=Academic Press|isbn=9780127445809}}</ref>

The [[conjugate base]] of squaric acid is the hydrogensquarate anion {{chem2|HC4O4−}}; and the conjugate base of the hydrogensquarate anion is the divalent squarate anion {{chem2|C4O4(2−)}}. This is one of the [[oxocarbon anion]]s, which consist only of carbon and oxygen.

Squaric acid is a reagent for [[chemical synthesis]], used for instance to make [[photosensitive]] [[squaraine dye]]s and inhibitors of [[protein tyrosine phosphatase]]s.

==Chemical properties==

Squaric acid is a white crystalline powder.<ref>{{cite journal | last1= Lee |first1=K.-S. |last2=Kweon |first2=J. J. |last3=Oh |first3=I.-H. |last4=Lee |first4=C. E. | year = 2012 | title = Polymorphic phase transition and thermal stability in squaric acid ({{chem|H|2|C|4|O|4|}}) | journal = J. Phys. Chem. Solids | volume = 73 | issue = 7| pages = 890–895 | doi = 10.1016/j.jpcs.2012.02.013}}</ref> The onset of thermal decomposition depends on the different thermodynamic conditions such as heating rates.

The structure of squaric acid is not a perfect square, as the carbon–carbon bond lengths are not quite equal. The high [[acidity]] with [[pKa|p''K''_a1]] = 1.5 for the first proton and p''K''_a2 = 3.4 for the second is attributable to [[resonance (chemistry)|resonance stabilization]] of the [[anion]].<ref name=west>{{cite journal | author1-link = Robert West (chemist)|first1=Robert|last1= West |first2=David L.|last2= Powell | year = 1963 | title = New Aromatic Anions. III. Molecular Orbital Calculations on Oxygenated Anions | journal = [[J. Am. Chem. Soc.]] | volume = 85 | issue = 17| pages = 2577–2579 | doi=10.1021/ja00900a010}}</ref> Because the negative charges are equally distributed between each oxygen atom, the dianion of squaric acid is completely symmetrical (unlike squaric acid itself) with all C−C [[bond length]]s identical and all C−O bond lengths identical.

{{multiple image

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| image1 = Squaric acid dianion.png

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| caption1 = Squaric acid dianion resonance forms

| image2 = Squarate-anion-3D-balls.png

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| caption2 = Ball-and-stick model of the squarate ion

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}}{{clear-left}}

==Derivatives==

Many of the reactions of squaric acid involve the OH groups. The molecule behaves similarly to a strong dicarboxylic acid. It is stronger acid than typical carboxylic acids.<ref>{{cite web |title=Acidity Tables for Heteroatom Organic Acids and Carbon Acids|url=https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/acidity2.htm}}</ref>

:{{chem2|C4O2(OH)2 → [C4O3(OH)]− + H+}}, [[pKa|p''K''_a1]] = 1.5

:{{chem2|[C4O3(OH)]− → [C4O4](2−) + H+}}, p''K''_a2 = 3.5

The OH groups are labile in squaric acid. It forms a dichloride with [[thionyl chloride]]:

:{{chem2|C4O2(OH)2 + 2 SOCl2 → C4O2Cl2 + 2 HCl + 2 SO2}}

The chlorides are good leaving groups, reminiscent of [[acid chloride]]s. They are displaced by diverse nucleophiles. In this way dithiosquarate can be prepared.<ref name=review>{{cite journal |title=Reaktionen von Quadratsäure und Quadratsäure-Derivaten|journal=Synthesis|year=1980|author=Arthur H. Schmidt|volume=1980|issue=12|page=961|doi=10.1055/s-1980-29291|s2cid=101871124 }}</ref>

The bis(methylether) is prepared by alkylation with [[trimethyl orthoformate]].<ref>{{cite journal |doi=10.15227/orgsyn.076.0189|title=Dimethyl Squarate and ITS Conversion to 3-Ethenyl-4-Methoxycyclobutene-1,2-Dione and 2-Butyl-6-Ethenyl-5-Methoxy-1,4-Benzoquinone|journal=Organic Syntheses|year=1999|volume=76|page=189 |first1=Hui |last1=Liu|first2=Craig S. |last2=Tomooka|first3=Simon L.|last3=Xu|first4=Benjamin R.|last4=Yerxa|first5=Robert W.|last5=Sullivan|first6=Yifeng|last6=Xiong|first7=Harold W.|last7=Moore}}</ref>

[[Dibutyl squarate]] is used for the treatment of warts<ref>{{cite journal | doi = 10.1067/mjd.2000.103631 | title = Squaric acid immunotherapy for warts in children | year = 2000 | last1 = Silverberg | first1 = Nanette B. | last2 = Lim | first2 = Joseph K. | last3 = Paller | first3 = Amy S. | last4 = Mancini | first4 = Anthony J. | journal = Journal of the American Academy of Dermatology | volume = 42 | issue = 5 | pages = 803–808 | pmid = 10775858}}</ref> and for [[alopecia areata ]].<ref>{{cite journal | doi = 10.1016/j.autrev.2016.02.021 | title = Modified immunotherapy for alopecia areata | year = 2016 | last1 = Yoshimasu | first1 = Takashi | last2 = Furukawa | first2 = Fukumi | journal = Autoimmunity Reviews | volume = 15 | issue = 7 | pages = 664–667 | pmid = 26932732}}</ref>

Diethyl squarate has been used as an intermediate in the synthesis of [[perzinfotel]].{{cn|date=January 2023}}

[[Squaramide]]s are prepared by displacement of alkoxy or chloride groups from {{chem2|C4O2X2}} (X = OR, Cl).<ref name=review/><ref>{{Cite journal | journal = Chem. Soc. Rev. | date = 2011 | volume = 40 | pages = 2330–2346 | doi = 10.1039/c0cs00200c | title=Squaramides: Physical Properties, Synthesis and Applications| last1 = Ian Storer | first1 = R. | last2 = Aciro | first2 = Caroline | last3 = Jones | first3 = Lyn H. | issue = 5 | pmid = 21399835}}</ref>

One or both of the oxygen (=O) groups in the squarate anion can be replaced by [[dicyanomethylene]] {{chem2|\dC(CN)2}}. The resulting anions, such as [[1,2-bis(dicyanomethylene)squarate]] and [[1,3-bis(dicyanomethylene)squarate]], retain the aromatic character of squarate and have been called [[pseudo-oxocarbon anion]]s.

[[Photolysis]] of squaric acid in a [[Matrix isolation|solid argon matrix]] at {{convert|10|K|C|0}} affords [[acetylenediol]].<ref>{{cite journal | last1= Maier |first1=Günther |last2=Rohr |first2=Christine | year = 1995 | title = Ethynediol: Photochemical generation and matrix-spectroscopic identification. | journal = Liebigs Annalen | volume = 1996 | issue = 3| pages = 307–309 | doi = 10.1002/jlac.199619960303}}</ref>

===Coordination complexes===

Squarate dianion behaves similarly to [[oxalate]], forming mono- and polynuclear complexes with hard metal ions.

[[Cobalt(II) squarate hydrate]] {{chem2|Co(C4O4)*2H2O}} (yellow, cubic) can be prepared by [[autoclave|autoclaving]] [[cobalt(II) hydroxide]] and squaric acid in water at 200&nbsp;°C. The water is bound to the [[cobalt]] atom, and the crystal structure consists of a cubic arrangement of hollow cells, whose walls are either six squarate anions (leaving a 7&nbsp;Å wide void) or several water molecules (leaving a 5&nbsp;Å void).<ref name=kuma>{{cite journal | first1= Kumagai|last1= Hitoshi |first2=Sobukawa |last2=Hideo |first3=Kurmoo |last3=Mohamedally | year = 2008 | title = Hydrothermal syntheses, structures and magnetic properties of coordination frameworks of divalent transition metals | journal = Journal of Materials Science | volume = 43 | issue = 7| pages = 2123–2130 | doi = 10.1007/s10853-007-2033-8 |bibcode= 2008JMatS..43.2123K |s2cid= 95205908}}</ref>

[[Cobalt(II) squarate dihydroxide]] {{chem2|Co3(OH)2(C4O4)2*3H2O}} (brown) is obtained together with the previous compound. It has a columnar structure including channels filled with water molecules; these can be removed and replaced without destroying the crystal structure. The chains are [[ferromagnetic]]; they are coupled antiferromagnetically in the hydrated form, ferromagnetically in the anhydrous form.<ref name=kuma/>

Copper(II) squarate monomeric and dimeric mixed-ligand complexes were synthesized and characterized.<ref>Reinprecht, J. T.; Miller, J. G.; Vogel, G. C.; et al. (1979). "Synthesis and Characterization of Copper(II) Squarate Complexes". Inorg. Chem., 19, 927-931</ref> Infrared, electronic and Q-Band EPR spectra as well as magnetic susceptibilities are reported.

The same method yields [[iron(II) squarate dihydroxide]] {{chem2|Fe2(OH)2(C4O4)}} (light brown).<ref name=kuma/>

== Synthesis ==

The original synthesis started with the ethanolysis of [[perfluorocyclobutene]] to give 1,2-diethoxy-3,3,4,4-tetrafluoro-1-cyclobutene. [[Hydrolysis]] gives the squaric acid.<ref>{{cite journal | title = Hydrolysis Reactions of Halogenated Cyclobutene Ethers: Synthesis of Diketocyclobutenediol |first1=J. D. |last1=Park |first2=S. |last2=Cohen |first3=J. R. |last3=Lacher |name-list-style=amp | journal = [[J. Am. Chem. Soc.]] |year = 1962 | volume = 84 | issue = 15 | pages = 2919–2922 | doi = 10.1021/ja00874a015}}</ref><ref name=Westbook/>

Although impractical, squarate and related anions such as [[deltic acid|deltate]] {{chem2|C3O3(2-)}} and [[acetylenediolate]] {{chem2|C2O2(2-)}} are obtainable by reductive coupling of carbon monoxide using [[organouranium chemistry|organouranium complexes]].<ref name=frey>{{cite journal | last1= Frey |first1=Alistair S. |last2=Cloke |first2=F. Geoffrey N. |last3=Hitchcock |first3=Peter B. | year = 2008 | title = Mechanistic Studies on the Reductive Cyclooligomerisation of CO by U(III) Mixed Sandwich Complexes; the Molecular Structure of [(U(η-C₈H₆{Si′Pr₃-1,4}₂)(η-Cp^*)]₂(μ-η¹:η¹-C₂O₂) | journal = Journal of the American Chemical Society | volume = 130 | issue = 42| pages = 13816–13817 | doi = 10.1021/ja8059792 |pmid=18817397}}</ref><ref name=summ2008>{{cite journal | last1= Summerscales |first1=Owen T. |last2=Frey |first2=Alistair S. P. |last3=Cloke |first3=F. Geoffrey N. |last4=Hitchcock |first4=Peter B. | year = 2009 | title = Reductive disproportionation of carbon dioxide to carbonate and squarate products using a mixed-sandwich U(III) complex | journal = Chemical Communications | issue = 2| pages = 198–200 | doi = 10.1039/b815576c |pmid=19099067}}</ref>

== See also ==

* [[Acetylenediol]], {{chem2|H2(CO)2}} or {{chem2|HO\sC\tC\sOH}}

* [[Deltic acid]], {{chem2|H2(CO)3}}

* [[Croconic acid]], {{chem2|H2(CO)5}}

* [[Rhodizonic acid]], {{chem2|H2(CO)6}}

* [[Cyclopropenone]], {{chem2|C3H2O}}

* [[Cyclobutene]], {{chem2|C4H6}}

* [[Squaramide]], {{chem2|C4O2(NH2)2}}, a [[nitrogen]] analog of squaric acid, where the [[Hydroxyl|OH groups]] of squaric acid are replaced by [[Amine|{{chem2|NH2}} groups]]

* [[Moniliformin]], {{chem2|NaC4HO3}}, the [[sodium]] [[Salt (chemistry)|salt]] of [[semisquaric acid]]

==References==

{{reflist|30em}}

{{Authority control}}

[[Category:Organic acids]]

[[Category:Diketones]]

[[Category:Enediols]]

[[Category:Cyclobutenes]]