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href="https://de.wikipedia.org/wiki/Quadrats%C3%A4ure" title="Quadratsäure – German" lang="de" hreflang="de" data-title="Quadratsäure" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/%C3%81cido_escu%C3%A1rico" title="Ácido escuárico – Spanish" lang="es" hreflang="es" data-title="Ácido escuárico" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Acide_squarique" title="Acide squarique – French" lang="fr" hreflang="fr" data-title="Acide squarique" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a 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page hosted by Wikidata [g]" accesskey="g"><span>Wikidata item</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> </div> </div> </div> <div class="vector-column-end"> <div class="vector-sticky-pinned-container"> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-pinned-container" class="vector-pinned-container"> </div> </nav> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-pinned-container" class="vector-pinned-container"> <div id="vector-appearance" class="vector-appearance vector-pinnable-element"> <div class="vector-pinnable-header vector-appearance-pinnable-header vector-pinnable-header-pinned" data-feature-name="appearance-pinned" data-pinnable-element-id="vector-appearance" data-pinned-container-id="vector-appearance-pinned-container" data-unpinned-container-id="vector-appearance-unpinned-container" > <div class="vector-pinnable-header-label">Appearance</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-appearance.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-appearance.unpin">hide</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><style data-mw-deduplicate="TemplateStyles:r1084375498">.mw-parser-output .ib-chembox{border-collapse:collapse;text-align:left}.mw-parser-output .ib-chembox td,.mw-parser-output .ib-chembox th{border:1px solid #a2a9b1;width:40%}.mw-parser-output .ib-chembox td+td{width:60%}</style> <table class="infobox ib-chembox"> <caption>Squaric acid<sup id="cite_ref-sigma_1-0" class="reference"><a href="#cite_note-sigma-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </caption> <tbody><tr> <td colspan="2" class="borderless" style="text-align:center"> <table border="0" style="width:100%;display:inline-table;"> <tbody><tr> <td style="border-right:1px solid #aaa; width:50%;"><figure class="mw-halign-center" typeof="mw:File"><a href="/wiki/File:Squaric_acid.svg" class="mw-file-description" title="Structural formula (carbon atoms omitted)"><img alt="Structural formula (carbon atoms omitted)" src="//upload.wikimedia.org/wikipedia/commons/thumb/b/bd/Squaric_acid.svg/110px-Squaric_acid.svg.png" decoding="async" width="110" height="101" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/bd/Squaric_acid.svg/165px-Squaric_acid.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/bd/Squaric_acid.svg/220px-Squaric_acid.svg.png 2x" data-file-width="179" data-file-height="165" /></a><figcaption>Structural formula (carbon atoms omitted)</figcaption></figure> </td> <td style="width:50%;"><figure class="mw-halign-center" typeof="mw:File"><a href="/wiki/File:Squaric-acid-3D-balls.png" class="mw-file-description" title="Ball-and-stick-model"><img alt="Ball-and-stick-model" src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Squaric-acid-3D-balls.png/110px-Squaric-acid-3D-balls.png" decoding="async" width="110" height="110" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Squaric-acid-3D-balls.png/165px-Squaric-acid-3D-balls.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Squaric-acid-3D-balls.png/220px-Squaric-acid-3D-balls.png 2x" data-file-width="1000" data-file-height="1000" /></a><figcaption>Ball-and-stick-model</figcaption></figure> </td></tr></tbody></table> </td></tr> <tr> <th colspan="2" style="background: #f8eaba; text-align: center;">Names </th></tr> <tr> <td colspan="2" style="text-align:left;"><a href="/wiki/Preferred_IUPAC_name" title="Preferred IUPAC name">Preferred IUPAC name</a> <div style="max-width:22em; word-wrap:break-word; padding-left:1.7em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0; max-width:22em;">3,4-Dihydroxycyclobut-3-ene-1,2-dione</div></div> </td></tr> <tr> <td colspan="2" style="text-align:left;">Other names <div style="max-width:22em; word-wrap:break-word; padding-left:1.7em;">Quadratic acid<br />Cyclobutenedioic acid</div> </td></tr> <tr> <th colspan="2" style="background: #f8eaba; text-align: center;">Identifiers </th></tr> <tr> <td><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/CAS_Registry_Number" title="CAS Registry Number">CAS Number</a></div> </td> <td><style data-mw-deduplicate="TemplateStyles:r1126788409">.mw-parser-output .plainlist ol,.mw-parser-output .plainlist ul{line-height:inherit;list-style:none;margin:0;padding:0}.mw-parser-output .plainlist ol li,.mw-parser-output .plainlist ul li{margin-bottom:0}</style><div class="plainlist"><ul><li><span title="commonchemistry.cas.org"><a rel="nofollow" class="external text" href="https://commonchemistry.cas.org/detail?cas_rn=2892-51-5">2892-51-5</a></span><sup> <span typeof="mw:File"><span><img alt="check" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png" decoding="async" width="7" height="7" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/11px-Yes_check.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/14px-Yes_check.svg.png 2x" data-file-width="600" data-file-height="600" /></span></span><span style="display:none">Y</span></sup></li></ul></div> </td></tr> <tr> <td><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">3D model (<a href="/wiki/JSmol" class="mw-redirect" title="JSmol">JSmol</a>)</div> </td> <td><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="chemapps.stolaf.edu (3D interactive model)"><a rel="nofollow" class="external text" href="https://chemapps.stolaf.edu/jmol/jmol.php?model=c1%28c%28c%28%3DO%29c1%3DO%29O%29O">Interactive image</a></span></li></ul></div> </td></tr> <tr> <td><a href="/wiki/ChemSpider" title="ChemSpider">ChemSpider</a> </td> <td><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="www.chemspider.com"><a rel="nofollow" class="external text" href="https://www.chemspider.com/Chemical-Structure.16919.html">16919</a></span><sup> <span typeof="mw:File"><span><img alt="check" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png" decoding="async" width="7" height="7" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/11px-Yes_check.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/14px-Yes_check.svg.png 2x" data-file-width="600" data-file-height="600" /></span></span><span style="display:none">Y</span></sup></li></ul></div> </td></tr> <tr> <td><a href="/wiki/ECHA_InfoCard" class="mw-redirect" title="ECHA InfoCard"><span title="echa.europa.eu">ECHA InfoCard</span></a> </td> <td><a rel="nofollow" class="external text" href="https://echa.europa.eu/substance-information/-/substanceinfo/100.018.875">100.018.875</a> <span class="mw-valign-text-top noprint" typeof="mw:File/Frameless"><a href="https://www.wikidata.org/wiki/Q903298#P2566" title="Edit this at Wikidata"><img alt="Edit this at Wikidata" src="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/10px-OOjs_UI_icon_edit-ltr-progressive.svg.png" decoding="async" width="10" height="10" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/15px-OOjs_UI_icon_edit-ltr-progressive.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/20px-OOjs_UI_icon_edit-ltr-progressive.svg.png 2x" data-file-width="20" data-file-height="20" /></a></span> </td></tr> <tr> <td><a href="/wiki/European_Community_number" title="European Community number"><span title="European Community number (chemical identifier)">EC Number</span></a> </td> <td><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li>220-761-4</li></ul></div> </td></tr> <tr> <td><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/PubChem" title="PubChem">PubChem</a> <abbr title="Compound ID">CID</abbr></div> </td> <td><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="pubchem.ncbi.nlm.nih.gov"><a rel="nofollow" class="external text" href="https://pubchem.ncbi.nlm.nih.gov/compound/17913">17913</a></span></li></ul></div> </td></tr> <tr> <td><a href="/wiki/Unique_Ingredient_Identifier" title="Unique Ingredient Identifier">UNII</a> </td> <td><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="precision.fda.gov"><a rel="nofollow" class="external text" href="https://precision.fda.gov/uniisearch/srs/unii/SVR9D0VODW">SVR9D0VODW</a></span><sup> <span typeof="mw:File"><span><img alt="check" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png" decoding="async" width="7" height="7" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/11px-Yes_check.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/14px-Yes_check.svg.png 2x" data-file-width="600" data-file-height="600" /></span></span><span style="display:none">Y</span></sup></li></ul></div> </td></tr> <tr> <td><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/CompTox_Chemicals_Dashboard" title="CompTox Chemicals Dashboard">CompTox Dashboard</a> <span style="font-weight:normal">(<abbr title="U.S. Environmental Protection Agency">EPA</abbr>)</span></div> </td> <td><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"><div class="plainlist"><ul><li><span title="comptox.epa.gov"><a rel="nofollow" class="external text" href="https://comptox.epa.gov/dashboard/chemical/details/DTXSID9049409">DTXSID9049409</a> <span class="mw-valign-text-top noprint" typeof="mw:File/Frameless"><a href="https://www.wikidata.org/wiki/Q903298#P3117" title="Edit this at Wikidata"><img alt="Edit this at Wikidata" src="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/10px-OOjs_UI_icon_edit-ltr-progressive.svg.png" decoding="async" width="10" height="10" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/15px-OOjs_UI_icon_edit-ltr-progressive.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/20px-OOjs_UI_icon_edit-ltr-progressive.svg.png 2x" data-file-width="20" data-file-height="20" /></a></span></span></li></ul></div> </td></tr> <tr> <td colspan="2"><div class="collapsible-list mw-collapsible mw-collapsed" style="text-align: left;"> <div style="line-height: 1.6em; font-weight: bold; text-align:left; font-weight:normal; background:transparent;"><div><a href="/wiki/International_Chemical_Identifier" title="International Chemical Identifier">InChI</a></div></div> <ul class="mw-collapsible-content" style="margin-top: 0; margin-bottom: 0; line-height: inherit; list-style: none; margin-left: 0; word-break:break-all;"><li style="line-height: inherit; margin: 0"><div style="border-top:1px solid #ccc; padding:0.2em 0 0.2em 1.5em; text-align:left;"><div style="word-wrap:break-word; text-indent:-1.5em; font-size:97%; line-height:120%;">InChI=1S/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H<sup> <span typeof="mw:File"><span><img alt="check" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png" decoding="async" width="7" height="7" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/11px-Yes_check.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/14px-Yes_check.svg.png 2x" data-file-width="600" data-file-height="600" /></span></span><span style="display:none">Y</span></sup></div><div style="word-wrap:break-word; text-indent:-1.5em; font-size:97%; line-height:120%;">Key: PWEBUXCTKOWPCW-UHFFFAOYSA-N<sup> <span typeof="mw:File"><span><img alt="check" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png" decoding="async" width="7" height="7" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/11px-Yes_check.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/14px-Yes_check.svg.png 2x" data-file-width="600" data-file-height="600" /></span></span><span style="display:none">Y</span></sup></div></div></li><li style="line-height: inherit; margin: 0"><div style="border-top:1px solid #ccc; padding:0.2em 0 0.2em 1.5em; text-align:left;"><div style="word-wrap:break-word; text-indent:-1.5em; font-size:97%; line-height:120%;">InChI=1/C4H2O4/c5-1-2(6)4(8)3(1)7/h5-6H</div><div style="word-wrap:break-word; text-indent:-1.5em; font-size:97%; line-height:120%;">Key: PWEBUXCTKOWPCW-UHFFFAOYAC</div></div></li></ul> </div> </td></tr> <tr> <td colspan="2"><div class="collapsible-list mw-collapsible mw-collapsed" style="text-align: left;"> <div style="line-height: 1.6em; font-weight: bold; text-align:left; font-weight:normal; background:transparent;"><div><a href="/wiki/Simplified_molecular-input_line-entry_system" class="mw-redirect" title="Simplified molecular-input line-entry system">SMILES</a></div></div> <ul class="mw-collapsible-content" style="margin-top: 0; margin-bottom: 0; line-height: inherit; list-style: none; margin-left: 0; word-break:break-all;"><li style="line-height: inherit; margin: 0"><div style="border-top:1px solid #ccc; padding:0.2em 0 0.2em 1.6em; word-wrap:break-word; text-indent:-1.5em; text-align:left; font-size:97%; line-height:120%;">c1(c(c(=O)c1=O)O)O</div></li></ul> </div> </td></tr> <tr> <th colspan="2" style="background: #f8eaba; text-align: center;">Properties </th></tr> <tr> <td><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/Chemical_formula" title="Chemical formula">Chemical formula</a></div> </td> <td><span title="Carbon">C</span><sub>4</sub><span title="Hydrogen">H</span><sub>2</sub><span title="Oxygen">O</span><sub>4</sub> </td></tr> <tr> <td><a href="/wiki/Molar_mass" title="Molar mass">Molar mass</a> </td> <td><span class="nowrap"><span data-sort-value="7002114056000000000♠"></span>114.056</span> g·mol<sup>−1</sup>   </td></tr> <tr> <td>Appearance </td> <td>white crystalline powder </td></tr> <tr> <td><a href="/wiki/Melting_point" title="Melting point">Melting point</a> </td> <td>> 300 °C (572 °F; 573 K) </td></tr> <tr> <td><a href="/wiki/Acid_dissociation_constant" title="Acid dissociation constant">Acidity</a> (p<i>K</i><sub>a</sub>) </td> <td>p<i>K</i><sub>a1</sub> = 1.5<br />p<i>K</i><sub>a2</sub> = 3.4 </td></tr> <tr> <th colspan="2" style="background: #f8eaba; text-align: center;">Hazards<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </th></tr> <tr> <td colspan="2" style="text-align:left; background-color:#eaeaea;"><a href="/wiki/Globally_Harmonized_System_of_Classification_and_Labelling_of_Chemicals" title="Globally Harmonized System of Classification and Labelling of Chemicals"><b>GHS</b> labelling</a>: </td></tr> <tr> <td style="padding-left:1em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/GHS_hazard_pictograms" title="GHS hazard pictograms">Pictograms</a></div> </td> <td><span typeof="mw:File"><a href="/wiki/File:GHS-pictogram-acid.svg" class="mw-file-description" title="GHS05: Corrosive"><img alt="GHS05: Corrosive" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a1/GHS-pictogram-acid.svg/50px-GHS-pictogram-acid.svg.png" decoding="async" width="50" height="50" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a1/GHS-pictogram-acid.svg/75px-GHS-pictogram-acid.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a1/GHS-pictogram-acid.svg/100px-GHS-pictogram-acid.svg.png 2x" data-file-width="724" data-file-height="724" /></a></span> </td></tr> <tr> <td style="padding-left:1em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/Globally_Harmonized_System_of_Classification_and_Labelling_of_Chemicals#Signal_word" title="Globally Harmonized System of Classification and Labelling of Chemicals">Signal word</a></div> </td> <td><b>Danger</b> </td></tr> <tr> <td style="padding-left:1em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/GHS_hazard_statements" title="GHS hazard statements">Hazard statements</a></div> </td> <td><abbr class="abbr" title="H314: Causes severe skin burns and eye damage">H314</abbr> </td></tr> <tr> <td style="padding-left:1em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/GHS_precautionary_statements" title="GHS precautionary statements">Precautionary statements</a></div> </td> <td><abbr class="abbr" title="P260: Do not breathe dust/fume/gas/mist/vapours/spray.">P260</abbr>, <abbr class="abbr" title="P280: Wear protective gloves/protective clothing/eye protection/face protection.">P280</abbr>, <abbr class="abbr" title="P301+P330+P331: IF SWALLOWED: Rinse mouth. Do NOT induce vomiting.">P301+P330+P331</abbr>, <abbr class="abbr" title="P303+P361+P353: IF ON SKIN (or hair): Remove/Take off immediately all contaminated clothing. Rinse skin with water [or shower].">P303+P361+P353</abbr>, <abbr class="abbr" title="P304+P340+P310: IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing. Immediately call a POISON CENTER or doctor/physician.">P304+P340+P310</abbr>, <abbr class="abbr" title="P305+P351+P338: IF IN EYES: Rinse continuously with water for several minutes. Remove contact lenses if present and easy to do. Continue rinsing.">P305+P351+P338</abbr> </td></tr> <tr> <td><a href="/wiki/Flash_point" title="Flash point">Flash point</a> </td> <td>190 °C (374 °F; 463 K)<sup id="cite_ref-alpha_3-0" class="reference"><a href="#cite_note-alpha-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </td></tr> <tr> <td colspan="2" style="text-align:left; background:#f8eaba; border:1px solid #a2a9b1;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Except where otherwise noted, data are given for materials in their <a href="/wiki/Standard_state" title="Standard state">standard state</a> (at 25 °C [77 °F], 100 kPa).</div> <div style="margin-top: 0.3em;"><div style="text-align:center;"><span typeof="mw:File"><span><img alt="check" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/12px-Yes_check.svg.png" decoding="async" width="12" height="12" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/18px-Yes_check.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/24px-Yes_check.svg.png 2x" data-file-width="600" data-file-height="600" /></span></span><span style="display:none">Y</span> <span class="reflink plainlinks nourlexpansion"><a class="external text" href="https://en.wikipedia.org/w/index.php?title=Special:ComparePages&rev1=470470338&page2=Squaric+acid">verify</a></span> (<a href="/wiki/Wikipedia:WikiProject_Chemicals/Chembox_validation" title="Wikipedia:WikiProject Chemicals/Chembox validation">what is</a> <sup><span typeof="mw:File"><span><img alt="check" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png" decoding="async" width="7" height="7" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/11px-Yes_check.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/14px-Yes_check.svg.png 2x" data-file-width="600" data-file-height="600" /></span></span><span style="display:none">Y</span><span typeof="mw:File"><span><img alt="☒" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/X_mark.svg/7px-X_mark.svg.png" decoding="async" width="7" height="8" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/X_mark.svg/11px-X_mark.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a2/X_mark.svg/14px-X_mark.svg.png 2x" data-file-width="525" data-file-height="600" /></span></span><span style="display:none">N</span></sup> ?) </div></div> <div style="margin-top: 0.3em; text-align: center;"><a href="/wiki/Wikipedia:Chemical_infobox#References" title="Wikipedia:Chemical infobox">Infobox references</a></div> </td></tr> </tbody></table><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Chemical compound</div> <p><b>Squaric acid</b>, also called <b>quadratic acid</b> because its four carbon atoms approximately form a square, is a <a href="/wiki/Polyprotic_acids" class="mw-redirect" title="Polyprotic acids">diprotic</a> <a href="/wiki/Organic_acid" title="Organic acid">organic acid</a> with the <a href="/wiki/Chemical_formula" title="Chemical formula">chemical formula</a> <style data-mw-deduplicate="TemplateStyles:r1123817410">.mw-parser-output .template-chem2-su{display:inline-block;font-size:80%;line-height:1;vertical-align:-0.35em}.mw-parser-output .template-chem2-su>span{display:block;text-align:left}.mw-parser-output sub.template-chem2-sub{font-size:80%;vertical-align:-0.35em}.mw-parser-output sup.template-chem2-sup{font-size:80%;vertical-align:0.65em}</style><span class="chemf nowrap">C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">2</sub>(OH)<sub class="template-chem2-sub">2</sub></span>.<sup id="cite_ref-Westbook_4-0" class="reference"><a href="#cite_note-Westbook-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p>The <a href="/wiki/Conjugate_base" class="mw-redirect" title="Conjugate base">conjugate base</a> of squaric acid is the hydrogensquarate anion <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">HC<sub class="template-chem2-sub">4</sub>O<span class="template-chem2-su"><span>−</span><span>4</span></span></span>; and the conjugate base of the hydrogensquarate anion is the divalent squarate anion <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">4</sub>O<span class="template-chem2-su"><span>2−</span><span>4</span></span></span>. This is one of the <a href="/wiki/Oxocarbon_anion" title="Oxocarbon anion">oxocarbon anions</a>, which consist only of carbon and oxygen. </p><p>Squaric acid is a reagent for <a href="/wiki/Chemical_synthesis" title="Chemical synthesis">chemical synthesis</a>, used for instance to make <a href="/wiki/Photosensitive" class="mw-redirect" title="Photosensitive">photosensitive</a> <a href="/wiki/Squaraine_dye" title="Squaraine dye">squaraine dyes</a> and inhibitors of <a href="/wiki/Protein_tyrosine_phosphatase" title="Protein tyrosine phosphatase">protein tyrosine phosphatases</a>. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Chemical_properties">Chemical properties</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Squaric_acid&action=edit&section=1" title="Edit section: Chemical properties"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Squaric acid is a white crystalline powder.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> The onset of thermal decomposition depends on the different thermodynamic conditions such as heating rates. </p><p>The structure of squaric acid is not a perfect square, as the carbon–carbon bond lengths are not quite equal. The high <a href="/wiki/Acidity" class="mw-redirect" title="Acidity">acidity</a> with <a href="/wiki/PKa" class="mw-redirect" title="PKa">p<i>K</i><sub>a1</sub></a> = 1.5 for the first proton and p<i>K</i><sub>a2</sub> = 3.4 for the second is attributable to <a href="/wiki/Resonance_(chemistry)" title="Resonance (chemistry)">resonance stabilization</a> of the <a href="/wiki/Anion" class="mw-redirect" title="Anion">anion</a>.<sup id="cite_ref-west_6-0" class="reference"><a href="#cite_note-west-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> 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 <a href="/wiki/Bond_length" title="Bond length">bond lengths</a> identical and all C−O bond lengths identical. </p> <style data-mw-deduplicate="TemplateStyles:r1237032888/mw-parser-output/.tmulti">.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner img{background-color:white}}</style><div class="thumb tmulti tleft"><div class="thumbinner multiimageinner" style="width:758px;max-width:758px"><div class="trow"><div class="tsingle" style="width:602px;max-width:602px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Squaric_acid_dianion.png" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Squaric_acid_dianion.png/600px-Squaric_acid_dianion.png" decoding="async" width="600" height="114" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Squaric_acid_dianion.png/900px-Squaric_acid_dianion.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Squaric_acid_dianion.png/1200px-Squaric_acid_dianion.png 2x" data-file-width="3131" data-file-height="594" /></a></span></div><div class="thumbcaption">Squaric acid dianion resonance forms</div></div><div class="tsingle" style="width:152px;max-width:152px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Squarate-anion-3D-balls.png" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Squarate-anion-3D-balls.png/150px-Squarate-anion-3D-balls.png" decoding="async" width="150" height="130" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Squarate-anion-3D-balls.png/225px-Squarate-anion-3D-balls.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Squarate-anion-3D-balls.png/300px-Squarate-anion-3D-balls.png 2x" data-file-width="1100" data-file-height="952" /></a></span></div><div class="thumbcaption">Ball-and-stick model of the squarate ion</div></div></div></div></div><div style="clear:left;" class=""></div> <div class="mw-heading mw-heading2"><h2 id="Derivatives">Derivatives</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Squaric_acid&action=edit&section=2" title="Edit section: Derivatives"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>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.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <dl><dd><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">2</sub>(OH)<sub class="template-chem2-sub">2</sub> → [C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">3</sub>(OH)]<sup class="template-chem2-sup">−</sup> + H<sup class="template-chem2-sup">+</sup></span>, <a href="/wiki/PKa" class="mw-redirect" title="PKa">p<i>K</i><sub>a1</sub></a> = 1.5</dd> <dd><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">[C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">3</sub>(OH)]<sup class="template-chem2-sup">−</sup> → [C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">4</sub>]<sup>2−</sup> + H<sup class="template-chem2-sup">+</sup></span>, p<i>K</i><sub>a2</sub> = 3.5</dd></dl> <p>The OH groups are labile in squaric acid. It forms a dichloride with <a href="/wiki/Thionyl_chloride" title="Thionyl chloride">thionyl chloride</a>: </p> <dl><dd><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">2</sub>(OH)<sub class="template-chem2-sub">2</sub> + 2 SOCl<sub class="template-chem2-sub">2</sub> → C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">2</sub>Cl<sub class="template-chem2-sub">2</sub> + 2 HCl + 2 SO<sub class="template-chem2-sub">2</sub></span></dd></dl> <p>The chlorides are good leaving groups, reminiscent of <a href="/wiki/Acid_chloride" class="mw-redirect" title="Acid chloride">acid chlorides</a>. They are displaced by diverse nucleophiles. In this way dithiosquarate can be prepared.<sup id="cite_ref-review_8-0" class="reference"><a href="#cite_note-review-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p><p>The bis(methylether) is prepared by alkylation with <a href="/wiki/Trimethyl_orthoformate" title="Trimethyl orthoformate">trimethyl orthoformate</a>.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Dibutyl_squarate" title="Dibutyl squarate">Dibutyl squarate</a> is used for the treatment of warts<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> and for <a href="/wiki/Alopecia_areata" title="Alopecia areata">alopecia areata </a>.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p><p>Diethyl squarate has been used as an intermediate in the synthesis of <a href="/wiki/Perzinfotel" title="Perzinfotel">perzinfotel</a>.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (January 2023)">citation needed</span></a></i>]</sup> </p><p><a href="/wiki/Squaramide" title="Squaramide">Squaramides</a> are prepared by displacement of alkoxy or chloride groups from <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">2</sub>X<sub class="template-chem2-sub">2</sub></span> (X = OR, Cl).<sup id="cite_ref-review_8-1" class="reference"><a href="#cite_note-review-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>One or both of the oxygen (=O) groups in the squarate anion can be replaced by <a href="/w/index.php?title=Dicyanomethylene&action=edit&redlink=1" class="new" title="Dicyanomethylene (page does not exist)">dicyanomethylene</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">=C(CN)<sub class="template-chem2-sub">2</sub></span>. The resulting anions, such as <a href="/wiki/1,2-bis(dicyanomethylene)squarate" class="mw-redirect" title="1,2-bis(dicyanomethylene)squarate">1,2-bis(dicyanomethylene)squarate</a> and <a href="/wiki/1,3-bis(dicyanomethylene)squarate" class="mw-redirect" title="1,3-bis(dicyanomethylene)squarate">1,3-bis(dicyanomethylene)squarate</a>, retain the aromatic character of squarate and have been called <a href="/wiki/Pseudo-oxocarbon_anion" title="Pseudo-oxocarbon anion">pseudo-oxocarbon anions</a>. </p><p><a href="/wiki/Photolysis" class="mw-redirect" title="Photolysis">Photolysis</a> of squaric acid in a <a href="/wiki/Matrix_isolation" title="Matrix isolation">solid argon matrix</a> at 10 K (−263 °C) affords <a href="/wiki/Acetylenediol" title="Acetylenediol">acetylenediol</a>.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Coordination_complexes">Coordination complexes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Squaric_acid&action=edit&section=3" title="Edit section: Coordination complexes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Squarate dianion behaves similarly to <a href="/wiki/Oxalate" title="Oxalate">oxalate</a>, forming mono- and polynuclear complexes with hard metal ions. <a href="/w/index.php?title=Cobalt(II)_squarate_hydrate&action=edit&redlink=1" class="new" title="Cobalt(II) squarate hydrate (page does not exist)">Cobalt(II) squarate hydrate</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">Co(C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">4</sub>)·2H<sub>2</sub>O</span> (yellow, cubic) can be prepared by <a href="/wiki/Autoclave" title="Autoclave">autoclaving</a> <a href="/wiki/Cobalt(II)_hydroxide" title="Cobalt(II) hydroxide">cobalt(II) hydroxide</a> and squaric acid in water at 200 °C. The water is bound to the <a href="/wiki/Cobalt" title="Cobalt">cobalt</a> atom, and the crystal structure consists of a cubic arrangement of hollow cells, whose walls are either six squarate anions (leaving a 7 Å wide void) or several water molecules (leaving a 5 Å void).<sup id="cite_ref-kuma_14-0" class="reference"><a href="#cite_note-kuma-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p><p><a href="/w/index.php?title=Cobalt(II)_squarate_dihydroxide&action=edit&redlink=1" class="new" title="Cobalt(II) squarate dihydroxide (page does not exist)">Cobalt(II) squarate dihydroxide</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">Co<sub class="template-chem2-sub">3</sub>(OH)<sub class="template-chem2-sub">2</sub>(C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">4</sub>)<sub class="template-chem2-sub">2</sub>·3H<sub>2</sub>O</span> (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 <a href="/wiki/Ferromagnetic" class="mw-redirect" title="Ferromagnetic">ferromagnetic</a>; they are coupled antiferromagnetically in the hydrated form, ferromagnetically in the anhydrous form.<sup id="cite_ref-kuma_14-1" class="reference"><a href="#cite_note-kuma-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p><p>Copper(II) squarate monomeric and dimeric mixed-ligand complexes were synthesized and characterized.<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> Infrared, electronic and Q-Band EPR spectra as well as magnetic susceptibilities are reported. </p><p>The same method yields <a href="/w/index.php?title=Iron(II)_squarate_dihydroxide&action=edit&redlink=1" class="new" title="Iron(II) squarate dihydroxide (page does not exist)">iron(II) squarate dihydroxide</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">Fe<sub class="template-chem2-sub">2</sub>(OH)<sub class="template-chem2-sub">2</sub>(C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">4</sub>)</span> (light brown).<sup id="cite_ref-kuma_14-2" class="reference"><a href="#cite_note-kuma-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Synthesis">Synthesis</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Squaric_acid&action=edit&section=4" title="Edit section: Synthesis"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The original synthesis started with the ethanolysis of <a href="/w/index.php?title=Perfluorocyclobutene&action=edit&redlink=1" class="new" title="Perfluorocyclobutene (page does not exist)">perfluorocyclobutene</a> to give 1,2-diethoxy-3,3,4,4-tetrafluoro-1-cyclobutene. <a href="/wiki/Hydrolysis" title="Hydrolysis">Hydrolysis</a> gives the squaric acid.<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Westbook_4-1" class="reference"><a href="#cite_note-Westbook-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p>Although impractical, squarate and related anions such as <a href="/wiki/Deltic_acid" title="Deltic acid">deltate</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">3</sub>O<span class="template-chem2-su"><span>2−</span><span>3</span></span></span> and <a href="/wiki/Acetylenediolate" class="mw-redirect" title="Acetylenediolate">acetylenediolate</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">2</sub>O<span class="template-chem2-su"><span>2−</span><span>2</span></span></span> are obtainable by reductive coupling of carbon monoxide using <a href="/wiki/Organouranium_chemistry" title="Organouranium chemistry">organouranium complexes</a>.<sup id="cite_ref-frey_17-0" class="reference"><a href="#cite_note-frey-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-summ2008_18-0" class="reference"><a href="#cite_note-summ2008-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Squaric_acid&action=edit&section=5" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Acetylenediol" title="Acetylenediol">Acetylenediol</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sub class="template-chem2-sub">2</sub>(CO)<sub class="template-chem2-sub">2</sub></span> or <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">HO−C≡C−OH</span></li> <li><a href="/wiki/Deltic_acid" title="Deltic acid">Deltic acid</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sub class="template-chem2-sub">2</sub>(CO)<sub class="template-chem2-sub">3</sub></span></li> <li><a href="/wiki/Croconic_acid" title="Croconic acid">Croconic acid</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sub class="template-chem2-sub">2</sub>(CO)<sub class="template-chem2-sub">5</sub></span></li> <li><a href="/wiki/Rhodizonic_acid" title="Rhodizonic acid">Rhodizonic acid</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">H<sub class="template-chem2-sub">2</sub>(CO)<sub class="template-chem2-sub">6</sub></span></li> <li><a href="/wiki/Cyclopropenone" title="Cyclopropenone">Cyclopropenone</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">3</sub>H<sub class="template-chem2-sub">2</sub>O</span></li> <li><a href="/wiki/Cyclobutene" title="Cyclobutene">Cyclobutene</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">4</sub>H<sub class="template-chem2-sub">6</sub></span></li> <li><a href="/wiki/Squaramide" title="Squaramide">Squaramide</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">C<sub class="template-chem2-sub">4</sub>O<sub class="template-chem2-sub">2</sub>(NH<sub class="template-chem2-sub">2</sub>)<sub class="template-chem2-sub">2</sub></span>, a <a href="/wiki/Nitrogen" title="Nitrogen">nitrogen</a> analog of squaric acid, where the <a href="/wiki/Hydroxyl" class="mw-redirect" title="Hydroxyl">OH groups</a> of squaric acid are replaced by <a href="/wiki/Amine" title="Amine"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">NH<sub class="template-chem2-sub">2</sub></span> groups</a></li> <li><a href="/wiki/Moniliformin" title="Moniliformin">Moniliformin</a>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">NaC<sub class="template-chem2-sub">4</sub>HO<sub class="template-chem2-sub">3</sub></span>, the <a href="/wiki/Sodium" title="Sodium">sodium</a> <a href="/wiki/Salt_(chemistry)" title="Salt (chemistry)">salt</a> of <a href="/wiki/Semisquaric_acid" class="mw-redirect" title="Semisquaric acid">semisquaric acid</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Squaric_acid&action=edit&section=6" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-sigma-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-sigma_1-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/123447">3,4-Dihydroxy-3-cyclobutene-1,2-dione</a>. <a href="/wiki/Sigma-Aldrich" title="Sigma-Aldrich">Sigma-Aldrich</a></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="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">"SICHERHEITSDATENBLATT"</a>. 21 March 2021.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=SICHERHEITSDATENBLATT&rft.date=2021-03-21&rft_id=https%3A%2F%2Fwww.merckmillipore.com%2FINTERSHOP%2Fweb%2FWFS%2FMerck-DE-Site%2Fde_DE%2F-%2FEUR%2FShowDocument-File%3FProductSKU%3DMDA_CHEM-803500%26DocumentId%3D803500_SDS_DE_DE.PDF%26DocumentType%3DMSD%26Language%3DDE%26Country%3DDE&rfr_id=info%3Asid%2Fen.wikipedia.org%3ASquaric+acid" class="Z3988"></span></span> </li> <li id="cite_note-alpha-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-alpha_3-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.alfa.com/en/GP100W.pgm?DSSTK=A15169">3,4-Dihydroxy-3-cyclobutene-1,2-dione, 98+%</a>. Alfa Aesar</span> </li> <li id="cite_note-Westbook-4"><span class="mw-cite-backlink">^ <a href="#cite_ref-Westbook_4-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Westbook_4-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRobert_West1980" class="citation book cs1">Robert West (1980). "History of the Oxocarbons". In Robert West (ed.). <i>Oxocarbons</i>. 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