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Revision as of 17:53, 9 January 2012 editBeetstra (talk | contribs)Edit filter managers, Administrators172,031 edits Saving copy of the {{chembox}} taken from revid 469308759 of page Squaric_acid for the Chem/Drugbox validation project (updated: '').		Latest revision as of 14:31, 25 January 2024 edit Maxim Masiutin (talk | contribs)Extended confirmed users, IP block exemptions, Pending changes reviewers30,619 edits Added s2cid.
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	{{ambox | text = This page contains a copy of the infobox ({{tl|chembox}}) taken from revid of page ] with values updated to verified values.}}
	{{chembox		{{chembox
	| Watchedfields = changed		|Watchedfields = changed
	| verifiedrevid = 440310522		|verifiedrevid = 470470338
	|Reference=<ref name=sigma>. ]</ref>		|Reference = <ref name=sigma>. ]</ref>
	|ImageFileL1 = Squaric acid.svg		|ImageFileL1 = Squaric acid.svg
	|ImageSizeL1 = 120px
	|ImageNameL1 = Structural formula (carbon atoms omitted)		|ImageNameL1 = Structural formula (carbon atoms omitted)
	|ImageFileR1 = Squaric-acid-3D-balls.png		|ImageFileR1 = Squaric-acid-3D-balls.png
	|ImageSizeR1 = 110px
	|ImageNameR1 = Ball-and-stick-model		|ImageNameR1 = Ball-and-stick-model
	|IUPACName = 3,4-Dihydroxycyclobut-3-ene-1,2-dione		|PIN = 3,4-Dihydroxycyclobut-3-ene-1,2-dione
	|OtherNames = Quadratic acid		|OtherNames = Quadratic acid<br/>Cyclobutenedioic acid
	|Section1={{Chembox Identifiers		|Section1={{Chembox Identifiers
	| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}		|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
	| ChemSpiderID = 16919		|ChemSpiderID = 16919
	| InChI = 1/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H		|EINECS = 220-761-4
			|InChI = 1/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H
	| InChIKey = PWEBUXCTKOWPCW-UHFFFAOYAC		|InChIKey = PWEBUXCTKOWPCW-UHFFFAOYAC
	| StdInChI_Ref = {{stdinchicite|correct|chemspider}}		|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
	| StdInChI = 1S/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H		|StdInChI = 1S/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H
	| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}		|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
	| StdInChIKey = PWEBUXCTKOWPCW-UHFFFAOYSA-N		|StdInChIKey = PWEBUXCTKOWPCW-UHFFFAOYSA-N
	| CASNo_Ref = {{cascite|correct|CAS}}		|CASNo_Ref = {{cascite|correct|CAS}}
	| CASNo=2892-51-5		|CASNo = 2892-51-5
			|UNII_Ref = {{fdacite|correct|FDA}}
	| PubChem=17913
			|UNII = SVR9D0VODW
	| SMILES = c1(c(c(=O)c1=O)O)O
			|PubChem = 17913
			|SMILES = c1(c(c(=O)c1=O)O)O
	}}		}}
	|Section2={{Chembox Properties		|Section2={{Chembox Properties
			|C=4 | H=2 | O=4
	| Formula=C<sub>4</sub>H<sub>2</sub>O<sub>4</sub>
			|Appearance = white crystalline powder
	| MolarMass=114.06 g/mol
			|MeltingPt= >
	| Appearance=Gray powder
			|MeltingPtC = 300
	| Density=
			|pKa = p''K''<sub>a1</sub> = 1.5<br>p''K''<sub>a2</sub> = 3.4
	| MeltingPt= >300&nbsp;°C
			}}
	| BoilingPt=
	| Solubility=
	}}
	|Section3={{Chembox Hazards		|Section3={{Chembox Hazards
			|FlashPtC = 190
	| MainHazards=
	| FlashPt=190&nbsp;°C<ref name=alpha>. Alfa Aesar</ref>		|FlashPt_ref = <ref name=alpha>. 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>
	| Autoignition=
	| RPhrases = {{R36/37/38}} {{R43}}		|GHSPictograms = {{GHS05}}
			|GHSSignalWord = Danger
	| SPhrases = {{S26}} {{S36}}
			|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 ] ] with the ] {{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 ] 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 ]s, which consist only of carbon and oxygen.
			Squaric acid is a reagent for ], used for instance to make ] ]s and inhibitors of ]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 ] with ] = 1.5 for the first proton and p''K''<sub>a2</sub> = 3.4 for the second is attributable to ] of the ].<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 = ] | 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 ]s identical and all C−O bond lengths identical.
			{{multiple image
			| align = left
			| image1 = Squaric acid dianion.png
			| width1 = 600
			| alt1 =
			| caption1 = Squaric acid dianion resonance forms
			| image2 = Squarate-anion-3D-balls.png
			| width2 = 150
			| alt2 =
			| caption2 = Ball-and-stick model of the squarate ion
			| footer =
			}}{{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 → − + H+}}, ] = 1.5
			:{{chem2|− → (2−) + H+}}, p''K''<sub>a2</sub> = 3.5
			The OH groups are labile in squaric acid. It forms a dichloride with ]:
			:{{chem2|C4O2(OH)2 + 2 SOCl2 → C4O2Cl2 + 2 HCl + 2 SO2}}
			The chlorides are good leaving groups, reminiscent of ]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 ].<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>
			] 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 ].<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 ].{{cn|date=January 2023}}
			]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 ] {{chem2|\dC(CN)2}}. The resulting anions, such as ] and ], retain the aromatic character of squarate and have been called ]s.
			] of squaric acid in a ] at {{convert|10|K|C|0}} affords ].<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 ], forming mono- and polynuclear complexes with hard metal ions.
			] {{chem2|Co(C4O4)*2H2O}} (yellow, cubic) can be prepared by ] ] and squaric acid in water at 200&nbsp;°C. The water is bound to the ] 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>
			] {{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 ]; 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 ] {{chem2|Fe2(OH)2(C4O4)}} (light brown).<ref name=kuma/>
			== Synthesis ==
			The original synthesis started with the ethanolysis of ] to give 1,2-diethoxy-3,3,4,4-tetrafluoro-1-cyclobutene. ] 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 = ] |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 ] {{chem2|C3O3(2-)}} and ] {{chem2|C2O2(2-)}} are obtainable by reductive coupling of carbon monoxide using ].<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 <sub>2</sub>(μ-η<sup>1</sup>:η<sup>1</sup>-C<sub>2</sub>O<sub>2</sub>) | 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 ==
			* ], {{chem2|H2(CO)2}} or {{chem2|HO\sC\tC\sOH}}
			* ], {{chem2|H2(CO)3}}
			* ], {{chem2|H2(CO)5}}
			* ], {{chem2|H2(CO)6}}
			* ], {{chem2|C3H2O}}
			* ], {{chem2|C4H6}}
			* ], {{chem2|C4O2(NH2)2}}, a ] analog of squaric acid, where the ] of squaric acid are replaced by ]
			* ], {{chem2|NaC4HO3}}, the ] ] of ]
			==References==
			{{reflist|30em}}
			{{Authority control}}
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