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{{Chembox {{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 416970903 | verifiedrevid = 416970903
| ImageFile = Rhodizonic acid.svg | ImageFile = Rhodizonic acid.svg
| ImageFile2 = Rhodizonic-acid-MMFF94s.png
| ImageSize =
| IUPACName = 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone | PIN = 5,6-Dihydroxycyclohex-5-ene-1,2,3,4-tetrone
| OtherNames = dihydroxydiquinoyl<br/>dioxydiquinone | OtherNames = dihydroxydiquinoyl<br/>dioxydiquinone
| Section1 = {{Chembox Identifiers |Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 118-76-3 | CASNo = 118-76-3
| CASNo_Comment = (dihydrate) | CASNo_Comment = (dihydrate)
⚫ | SMILES = C1(=C(C(=O)C(=O)C(=O)C1=O)O)O
⚫ | PubChem =
| EINECS = 204-276-5
⚫ | SMILES = c1(c(c(=O)c(=O)c(=O)c1=O)O)O }}
⚫ | PubChem = 67050
⚫ | Section2 = {{Chembox Properties
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| Formula = C<sub>6</sub>H<sub>2</sub>O<sub>6</sub>
| MolarMass = | ChemSpiderID = 60401
| InChI = 1/C6H2O6/c7-1-2(8)4(10)6(12)5(11)3(1)9/h7-8H
| Appearance =
| InChIKey = WCJLIWFWHPOTAC-UHFFFAOYAV
| Density =
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| MeltingPt = 130-132&deg;C
| StdInChI = 1S/C6H2O6/c7-1-2(8)4(10)6(12)5(11)3(1)9/h7-8H
| BoilingPt =
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
| Solubility = }}
| StdInChIKey = WCJLIWFWHPOTAC-UHFFFAOYSA-N
| Section3 = {{Chembox Hazards
| MeSHName = C005690}}
| MainHazards =
⚫ |Section2={{Chembox Properties
| FlashPt =
| Autoignition = }} | Formula = {{chem2|H2C6O6}}
| H=2|C=6|O=6
| Appearance = Orange to deep-red highly ] crystals
| MeltingPtC = 130 to 132
}} }}
}}
'''Rhodizonic acid''' is a ] with formula C<sub>6</sub>H<sub>2</sub>O<sub>6</sub> or (CO)<sub>4</sub>(COH)<sub>2</sub>. It can be seen as a two-fold ] and four-fold ] of ], more precisely '''5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone'''. '''Rhodizonic acid''' is a ] with formula {{chem2|H2C6O6}} or {{chem2|(CO)4(COH)2}}. It can be seen as a twofold ] and fourfold ] of ], more precisely '''5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone'''.


Rhodizonic acid is usually obtained in the form of a colorless "dihydrate" C<sub>6</sub>H<sub>2</sub>O<sub>6</sub>·2H<sub>2</sub>O. The latter is actually 2,3,5,5,6,6-hexahydroxycyclohex-2-ene-1,4-dione, where two of the original ketone groups are replaced by two pairs of geminal hydroxyls. The orange to deep-red and highly ] anhydrous acid can be obtained by low-pressure sublimation of the dihydrate.<ref name="patton"> Rhodizonic acid is usually obtained in the form of a ] {{chem2|H2C6O6*2H2O}}. The latter is actually 2,3,5,5,6,6-hexahydroxycyclohex-2-ene-1,4-dione, where two of the original ketone groups are replaced by two pairs of ]s. The orange to deep-red and highly ] anhydrous acid can be obtained by low-pressure sublimation of the dihydrate.<ref name="patton">{{cite journal|first1=E. |last1=Patton |first2=R. |last2=West |date=1970 |title=New aromatic anions. VIII. Acidity constants of rhodizonic acid |journal=Journal of Physical Chemistry |volume=74 |issue=12 |page=2512–2518 |doi=10.1021/j100706a018}}</ref><ref name="braga2">{{cite journal|first1=D. |last1=Braga |first2=G. |last2=Cojazzi |first3=L. |last3=Maini |first4=F. |last4=Grepioni |date=2001 |title=Reversible solid-state interconversion of rhodizonic acid H<sub>2</sub>C<sub>6</sub>O<sub>6</sub> into H<sub>6</sub>C<sub>6</sub>O<sub>8</sub> and the solid-state structure of the rhodizonate dianion {{chem|C|6|O|6|2-}} (aromatic or non-aromatic?) |journal=New Journal of Chemistry |volume=25 |page=1221−1223 |doi=10.1039/b107317f}}</ref>
Elizabeth Patton, Robert West (1970), ''New aromatic anions. VIII. Acidity constants of rhodizonic acid''. J. Phys. Chem., volume 74 issue 12, pp 2512–2518. {{doi|10.1021/j100706a018}}
</ref><ref name="braga2">
Dario Braga, Gianna Cojazzi, Lucia Maini and Fabrizia Grepioni (2001), ''Reversible solid-state interconversion of rhodizonic acid H2C6O6 into H6C6O8 and the solid-state structure of the rhodizonate dianion C6O62 – (aromatic or non-aromatic?)''. New J. Chem., volume 25, pages 1221 - 1223. {{doi|10.1039/b107317f}}
</ref>


Like many other enols, rhodizonic acid can lose the ] {{chem2|H+}} from the hydroxyls (p''K''<sub>a1</sub>&nbsp;= {{val|4.378|0.009}}, p''K''<sub>a2</sub>&nbsp;= {{val|4.652|0.014}} at 25&nbsp;°C),<ref name="gelb1">{{cite journal|first1=R. I. |last1=Gelb |first2=L. M. |last2=Schwartz |first3=D. A. |last3=Laufer |date=1978 |title=The structure of aqueous rhodizonic acid |journal=Journal of Physical Chemistry |volume=82 |issue=18 |page=1985–1988 |doi=10.1021/j100507a006}}</ref> yielding the '''hydrogen rhodizonate''' anion {{chem2|HC6O6-}} and the '''rhodizonate''' anion {{chem2|C6O6(2-)}}. The latter is aromatic and symmetric, as the ] and the negative charges are ] and evenly distributed over the six ] units. Rhodizonates tend to have various shades of red, from yellowish to purplish.
Like many other alcohols, rhodizonic acid can lose the ] H<sup>+</sup> from the hydroxyls (pK<sub>1</sub> = 4.378 ± 0.009, pK<sub>2</sub> = 4.652 ± 0.014 at 25°C),<ref name="gelb1">
R. I. Gelb, L. M. Schwartz, D. A. Laufer (1978), ''The structure of aqueous rhodizonic acid''. J. Phys. Chem., volume 82 issue 18, pp. 1985–1988.
{{doi|10.1021/j100507a006}}
</ref> yielding the '''hydrogenrhodizonate''' anion C<sub>6</sub>HO<sub>6</sub><sup>&minus;</sup> and the '''rhodizonate''' anion C<sub>6</sub>O<sub>6</sub><sup>2&minus;</sup>. The latter is aromatic and symmetric, as the double bond and the negative charges are delocalized and evenly distributed over the six CO units. Rhodizonates tend to have various shades of red, from yellowish to purplish.


Rhodizonic acid has been used in chemical assays for ], ], and other metals.<ref name="chalmers">{{cite journal|first1=R. A. |last1=Chalmers |first2=G. M. |last2=Telling |date=1967 |title=A reassessment of rhodizonic acid as a qualitative reagent |journal=Microchimica Acta |volume=55 |issue=6 |page=1126–1135 |doi=10.1007/BF01225955|s2cid=98540174}}</ref> In particular, the sodium rhodizonate test can be used to detect ] (which contains lead) in a subject's hands,<ref>{{cite book |first=V. J. M. |last1=Di Maio |title=Gunshot Wounds: Practical aspects of firearms, ballistics, and forensic techniques |edition=2nd |publisher=CRC |date=1998 |isbn=0-8493-8163-0 |page= |url=https://archive.org/details/gunshotwoundspra00dima/page/341}}</ref> and to distinguish ] wounds from gunshot wounds for hunting regulation enforcement.<ref name="Glover">{{cite journal|first1=R. L. |last1=Glover |date=1981 |title=Detecting lead in "arrow" wounds in deer using rhodizonic acid |journal=Wildlife Society Bulletin |volume=9 |issue=3 |pages=216–219 |jstor=3781843}}</ref>
Rhodizonic acid has been used in chemical assays for ], ], and other metals.<ref name="chalmers">
Robert A. Chalmers and Geoffrey M. Telling (1967), ''A reassessment of rhodizonic acid as a qualitative reagent''. Microchimica Acta, Volume 55, Number 6, pages 1126-1135. {{doi|10.1007/BF01225955}}
</ref> In particular, the ] can be used to detect ] (which contains lead) in a subject's hands,<ref>
Vincent J. M. Di Maio, ''Gunshot wounds: practical aspects of firearms, ballistics, and forensic techniques, 2nd edition. CRC, 1998. ISBN 0849381630. p. 341.
</ref> and to distinguish ] wounds from gunshot wounds for hunting regulation enforcement.<ref name="Glover">
Ronald L. Glover (1981), ''Detecting Lead in "Arrow" Wounds in Deer Using Rhodizonic Acid'' Wildlife Society Bulletin, Vol. 9, No. 3, pp. 216-219. accessed on 2009-07-30.
</ref>


==History== ==History==
Rhodizonic acid was discovered by ] chemist ] in 1837, by analyzing the products of heating a mixture of ] and ].<ref name="heller">{{cite journal|authorlink=Johann Florian Heller |first=J. F. |last=Heller |date=1837 |title=Die Rhodizonsäure, eine aus den Produkten der Kaliumbereitung gewonnene neue Säure, und ihre chemischen Verhältnisse |trans-title=Rhodizonic acid, one of the new acids derived from potassium preparations, and its chemical composition |journal=Justus Liebigs Annalen der Pharmacie |volume=24 |issue=1 |page=1–16 |url=https://books.google.com/books?id=WGkTAAAAQAAJ&pg=RA2-PA1 |access-date=2009-07-08}}</ref><ref name="turner">{{cite book|author1-link=Edward Turner (chemist) |first1=E. |last1=Turner |author2-link=William Gregory (chemist) |first2=W. |last2=Gregory |first3=E. A. |last3=Parnell |author4-link=Justus Liebig |first4=J. |last4=Liebig |author5-link=James Blythe Rogers |first5=J. B. |last5=Rogers |date=1846 |title=Elements of Chemistry |publisher=Thomas, Cowperthwait & Co. |url=https://books.google.com/books?id=j1jPAAAAMAAJ |accessdate=2009-07-30 |quote=When ] is heated in ], combination takes place, and a dark olive powder is formed, composed of carbonic oxide and potassium, in the proportion C<sub>7</sub>O<sub>7</sub>+K<sub>3</sub>, or 7CO+3K. This substance is formed in large quantity in the preparation of potassium from ] and ], and is the source of great loss and inconvenience. No such compound is formed with sodium, for which reason that metal may be more cheaply prepared than potassium.}}</ref><ref name="loewig1">{{cite book|first=C. |last1=Löwig |date=1839 |title=Chemie der organischen Verbindungen |trans-title=Chemistry of Organic Compounds |publisher=F. Schultess |location=Zürich}}</ref> The name comes from ] {{lang|grc|ῥοδίζω}} (''rhodizō'', "to tinge red"),<ref name="hunter">{{cite book|editor1-first=R. |editor1-last=Hunter |editor2-first=C. |editor2-last=Morris |date=1900 |title=Universal Dictionary of the English language |publisher=Collier |location=New York
Rhodizonic acid was discovered by ] chemist ] in 1837, by analyzing the products of heating a mixture of potassium carbonate and charcoal.<ref name="heller">
⚫ |url=https://archive.org/stream/universaldiction04huntuoft#page/4005 |accessdate=2009-08-07}}</ref> on account of the color of its salts.
Johann Florian Heller (1837), ''Die Rhodizonsäure, eine aus den Produkten der Kaliumbereitung gewonnene neue Säure, und ihre chemischen Verhältnisse'', Justus Liebigs Annalen der Pharmacie, volume 24, issue 1, pp. 1–16. accessed on 2009-07-08.
</ref><ref name="turner">
Edward Turner, William Gregory, Edward Andrew Parnell, Justus Liebig, James B. Rogers (1846), ''Elements of chemistry''. Thomas, Cowperthwait & Co. accessed on 2009-07-30. "When potassium is heated in carbonic acid gas, combination takes place, and a dark olive powder is formed, composed of carbonic oxide and potassium, in the proportion C<sub>7</sub>O<sub>7</sub>+K<sub>3</sub>, or 7CO+3K. This substance is formed in large quantity in the preparation of potassium from ] and ], and is the source of great loss and inconvenience. No such compound is formed with sodium, for which reason that metal may be more cheaply prepared than potassium."
</ref><ref name="loewig1">
Carl Löwig (1839), ''Chemie der organischen Verbindungen''. F. Schultess, Zürich.
</ref> For a while, rhodizonates were believed to have the formula C<sub>7</sub>O<sub>7</sub> · Me<sub>3</sub>.<ref name="loewig2">
Carl Löwig, Daniel Breed ''Principles of organic and physiological chemistry''. accessed on 2009-07-30.
</ref> The name comes from ] ''ῥοδίζω'' (''rhodizō'', "to tinge red"),<ref name="">
Robert Hunter and Charles Morris (1900), ''Universal dictionary of the English language''. Collier, NY.
⚫ accessed on 2009-08-07.
</ref> on account of the color of its salts.


==Chemistry== ==Chemistry==
Line 62: Line 46:
Rhodizonates tend to have various shades of red, from yellowish to purplish, in transmitted light, with a greenish luster in reflected light. Rhodizonates tend to have various shades of red, from yellowish to purplish, in transmitted light, with a greenish luster in reflected light.


] rhodizonate can be prepared with good yield and purity by oxidizing ] with ] and reacting the result with ] in the presence of oxygen. The rhodizonate crystallizes out of the solution due to its relative insolubility in water.<ref name="preisler"> ] rhodizonate can be prepared with good yield and purity by oxidizing ] with ] and reacting the result with ] in the presence of oxygen. The rhodizonate crystallizes out of the solution due to its relative insolubility in water.<ref name="preisler">{{cite journal|first1=P. W. |last1=Preisler |first2=L. |last2=Berger |date=1942 |title=Preparation of Tetrahydroxyquinone and Rhodizonic Acid Salts from the Product of the Oxidation of Inositol with Nitric Acid |journal=Journal of the American Chemical Society |volume=64 |issue=1 |page=67–69 |doi=10.1021/ja01253a016}}</ref>
Paul W. Preisler and Louis Berger (1942), ''Preparation of Tetrahydroxyquinone and Rhodizonic Acid Salts from the Product
of the Oxidation of Inositol with Nitric Acid''. Journal of the American Chemical Society, volume 64 issue 1, pp 67–69. {{doi|10.1021/ja01253a016}}
</ref>


] rhodizonate is dark brown and stable when dry,<ref name="feigl"/> but the aqueous solution decomposes in a few days, even in the refrigerator.<ref name="chalmers"/> ] rhodizonate is dark violet. <ref name="feigl"> ] rhodizonate is dark brown and stable when dry,<ref name="feigl"/> but the aqueous solution decomposes in a few days, even in the refrigerator.<ref name="chalmers"/> ] rhodizonate is dark violet.<ref name="feigl">{{cite book|first1=F. |last1=Feigl |first2=R. E. |last2=Oesper |title=Spot Tests in Organic Analysis |url=https://books.google.com/books?id=4I9qAAAAMAAJ |accessdate=2009-07-30|year=1960}}</ref><ref name="gmelinwa">{{cite book|author1-link=Leopold Gmelin |first1=L. |last1=Gmelin |author2-link=Henry Watts (chemist) |first2=H. |last2=Watts |date=1856 |title=Hand-book of Chemistry |publisher=Cavendish Society}}</ref>
Fritz Feigl, Ralph E. Oesper, ''Spot tests in organic analysis''. accessed on 2009-07-30.
</ref><ref name="gmelinwa">
Leopold Gmelin, Henry Watts (1856), ''Hand-book of chemistry''. Cavendish Society
</ref>


===Oxidation and decomposition=== ===Oxidation and decomposition===
Rhodizonic acid is a member of a chain of oxidation products: ] (COH)<sub>6</sub>, ] (COH)<sub>4</sub>(CO)<sub>2</sub>, rhodizonic acid (COH)<sub>2</sub>(CO)<sub>4</sub>, and ] (CO)<sub>6</sub>.<ref name="chalmers"/>. Lithium rhodizonate, together with salts of THBQ and benzenehexol, has been considered for possible use in rechargeable ].<ref name="chen"> Rhodizonic acid is a member of a chain of oxidation products: ] {{chem2|(COH)6}}, ] (THBQ) {{chem2|(COH)4(CO)2}}, rhodizonic acid {{chem2|(COH)2(CO)4}}, and the fleeting ] {{chem2|(CO)6}}.<ref name="chalmers"/> Lithium rhodizonate, together with salts of THBQ and benzenehexol, has been considered for possible use in rechargeable ].<ref name="chen">{{cite journal|first1=H. |last1=Chen |first2=M. |last2=Armand |first3=M. |last3=Courty |first4=M. |last4=Jiang |first5=C. P. |last5=Grey |first6=F. |last6=Dolhem |first7=J.-M. |last7=Tarascon |first8=P. |last8=Poizot |date=2009 |title=Lithium salt of tetrahydroxybenzoquinone: toward the development of a sustainable Li-ion battery |journal=Journal of the American Chemical Society |volume=131 |issue=25 |pages=8984–8 |doi=10.1021/ja9024897|pmid=19476355}}</ref> The monovalent anion {{chem|C|6|O|6|-}} has been detected in mass spectrometry experiments.<ref name=wyja>{{cite journal|first1=R. B. |last1=Wyrwas |first2=C. |last2=Chick Jarrold |date=2006 |title=Production of {{chem|C|6|O|6|-}} from oligomerization of CO on molybdenum anions |journal=Journal of the American Chemical Society |volume=128 |issue=42 |pages=13688–9 |doi=10.1021/ja0643927|pmid=17044687}}</ref>
Haiyan Chen, Michel Armand, Matthieu Courty, Meng Jiang, Clare P. Grey, Franck Dolhem, Jean-Marie Tarascon, and Philippe Poizot (2009), ''Lithium Salt of Tetrahydroxybenzoquinone: Toward the Development of a Sustainable Li-Ion Battery'' J. Am. Chem. Soc., 131 (25), pp. 8984–8988 {{doi|10.1021/ja9024897}}
</ref> The monovalent anion {{chem|C|6|O|6|-}} has been detected in mass spectrometry experiments.<ref name=wyja>
Richard B. Wyrwas and Caroline Chick Jarrold (2006), ''Production of C6O6- from Oligomerization of CO on Molybdenum Anions''. J. Am. Chem. Soc. volume 128 issue 42, pages 13688–13689. {{doi|10.1021/ja0643927}}
</ref>


Rhodizonic acid and the rhodizonate anion can lose one of the CO units to yield ] (CO)<sub>3</sub>(COH)<sub>2</sub> and the croconate anion C<sub>5</sub>O<sub>5</sub><sup>2&minus;</sup>, respectively, by mechanisms that are still imperfectly known. In basic solutions (pH > 10), rhodizonic acid quickly converts to the THBQ anion (CO)<sub>6</sub><sup>4&minus;</sup> in the absence of oxygen, and to croconic acid in its presence. At pH 8.3 and exposure to light, solutions are stable for days in the absence of oxygen, and decompose to croconic acid and other products (possibly including ] or ]) in its presence.<ref name="iraci"> Rhodizonic acid and the rhodizonate anion can lose one of the CO units to yield ] {{chem2|(CO)3(COH)2}} and the croconate anion {{chem2|C5O5(2-)}}, respectively, by mechanisms that are still imperfectly known. In basic solutions (pH&nbsp;>&nbsp;10), rhodizonic acid quickly converts to the THBQ anion {{chem2|(CO)6(4-)}} in the absence of oxygen, and to croconic acid in its presence. At pH&nbsp;8.3 and exposure to light, solutions are stable for days in the absence of oxygen, and decompose to croconic acid and other products (possibly including ] or ]) in its presence.<ref name="iraci">{{cite journal|first1=G. |last1=Iraci |first2=M. H. |last2=Back |date=1988 |title=The photochemistry of the rhodizonate dianion in aqueous solution |journal=Canadian Journal of Chemistry |volume=66 |issue=5 |page=1293 |doi=10.1139/v88-209 |doi-access=free}}</ref><ref name="zhao">{{cite journal|first1=B. |last1=Zhao |first2=M. H. |last2=Back |date=1991 |title=The photochemistry of the rhodizonate dianion in aqueous solution |journal=Canadian Journal of Chemistry |volume=69 |issue=3 |page=528 |url=http://article.pubs.nrc-cnrc.gc.ca/RPAS/rpv?hm=HInit&afpf=v91-079.pdf&journal=cjc&volume=69 |archive-url=https://archive.today/20120707084126/http://article.pubs.nrc-cnrc.gc.ca/RPAS/rpv?hm=HInit&afpf=v91-079.pdf&journal=cjc&volume=69 |url-status=dead |archive-date=2012-07-07 |accessdate=2009-08-07|doi=10.1139/v91-079 |doi-access=free}}</ref>
G. Iraci and M. H. Back (1988), ''The photochemistry of the rhodizonate dianion in aqueous solution.'' Canadian Journal of Chemistry, volume 66, page 1293. accessed on 2009-08-07.
</ref><ref name="zhao">
B. Zhao and M. H. Back (1991), ''The photochemistry of the rhodizonate dianion in aqueous solution.'' Canadian Journal of Chemistry, volume 69, page 528. accessed on 2009-08-07.
</ref>


==Structure== ==Structure==
===Acid=== ===Acid===
In solution, the acid and the hydrogenrhodizonate ion are mostly hydrated, with some of the ketone groups C=O replaced by geminal hydroxyls, C(OH)<sub>2</sub><ref name="gelb1"/> In solution, the acid and the hydrogen rhodizonate ion are mostly hydrated, with some of the carbonyl groups >C=O replaced by geminal hydroxyls, {{chem2|>C(OH)2}}.<ref name="gelb1"/>


===Salts=== ===Salts===
]]
In anhydrous ] rhodizonate 2Rb<sup>+</sup> · C<sub>6</sub>O<sub>6</sub><sup>2&minus;</sup>, the rhodizonate anions are stacked in parallel columns, and so are the rubidium ions. In the plane perpendicular to the columns, these are arranged as two interleaved hexagonal grids. The anions are planar.<ref name="braga2"/> In anhydrous ] rhodizonate {{chem2|(Rb+)2(2-)}}, the rhodizonate anions are stacked in parallel columns, as are the rubidium ions. In the plane perpendicular to the columns, these are arranged as two interleaved hexagonal grids. The anions are planar.<ref name="braga2"/>


Anhydrous potassium rhodizonate 2K<sup>+</sup> · C<sub>6</sub>O<sub>6</sub><sup>2&minus;</sup> has a distinct but similar structure. The anions and cations are arranged in alternate planes. Within each plane, the anions are arranged in an haexaginal grid. Each K ion is arranged so that it connects symmetrically to eight oxygens of four anions, two from each adjacent plane. The anions are slightly twisted in the "boat" shape (with 0.108 Å of rms deviation from mean plane).<ref name="cowan"> Anhydrous potassium rhodizonate {{chem2|(K+)2(2-)}} has a distinct but similar structure. The anions and cations are arranged in alternate planes. Within each plane, the anions are arranged in a hexagonal grid. Each potassium ion is arranged so that it connects symmetrically to eight oxygens of four anions, two from each adjacent plane. The anions are slightly twisted in the ] (with 0.108&nbsp;Å of ] deviation from mean plane).<ref name="cowan">{{cite journal|first1=J. A. |last1=Cowan |first2=J. A. K. |last2=Howard |date=2004 |title=Dipotassium rhodizonate |journal=Acta Crystallographica |volume=E60 |issue=4 |page=m511–m513 |doi=10.1107/S160053680400529X|doi-access=free}}</ref> Sodium rhodizonate {{chem2|(Na+)2(2-)}} has the same structure, with slightly more distorted anions (0.113&nbsp;Å rms)<ref name="dinne">{{cite journal|first1=R. E. |last1=Dinnebier |first2=H. |last2=Nuss |first3=M. |last3=Jansen |date=2005 |title=Disodium rhodizonate: a powder diffraction study |journal=Acta Crystallographica |volume=E61 |issue=10 |page=m2148–m2150 |doi=10.1107/S1600536805030552}}</ref>
J. A. Cowan and J. A. K. Howard (2004), ''Dipotassium rhodizonate''. Acta Crystallographica, volume E60, pages m511-m513. {{doi|10.1107/S160053680400529X}}
</ref> Sodium rhodizonate 2Na<sup>+</sup> · C<sub>6</sub>O<sub>6</sub><sup>2&minus;</sup> has the same structure, with slightly more distorted anions (0.113 Å rms)<ref name="dinne">
R. E. Dinnebier, H. Nuss and M. Jansen (2005), ''Disodium rhodizonate: a powder diffraction study.'' Acta Crystallographica, volume E61, pages m2148-m2150. {{doi|10.1107/S1600536805030552}}
</ref>


In solution, the rhodizonate anion is not hydrated.<ref name="gelb1"/> In solution, the rhodizonate anion is not hydrated.<ref name="gelb1"/>


==See also== ==See also==
* ] (COH)<sub>2</sub> * ] {{chem2|(COH)2}}
* ] (CO)(COH)<sub>2</sub> * ] {{chem2|(CO)(COH)2}}
* ] (CO)<sub>2</sub>(COH)<sub>2</sub> * ] {{chem2|(CO)2(COH)2}}
* ] (CO)<sub>3</sub>(COH)<sub>2</sub> * ] {{chem2|(CO)3(COH)2}}


==References== ==References==
{{reflist}} {{reflist}}


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⚫ ]
<!--ΔS<sub>1 = -4.6 ± 0.8, ΔS<sub>2 = 11 ± 1 cal mol<sup>&minus;1</sup> K<sup>&minus;1</sup> --> <!--ΔS<sub>1 = -4.6 ± 0.8, ΔS<sub>2 = 11 ± 1 cal mol<sup>&minus;1</sup> K<sup>&minus;1</sup> -->


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Latest revision as of 13:49, 19 July 2024

Rhodizonic acid
Names
Preferred IUPAC name 5,6-Dihydroxycyclohex-5-ene-1,2,3,4-tetrone
Other names dihydroxydiquinoyl
dioxydiquinone
Identifiers
CAS Number
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.003.888 Edit this at Wikidata
EC Number
  • 204-276-5
MeSH C005690
PubChem CID
CompTox Dashboard (EPA)
InChI
  • InChI=1S/C6H2O6/c7-1-2(8)4(10)6(12)5(11)3(1)9/h7-8HKey: WCJLIWFWHPOTAC-UHFFFAOYSA-N
  • InChI=1/C6H2O6/c7-1-2(8)4(10)6(12)5(11)3(1)9/h7-8HKey: WCJLIWFWHPOTAC-UHFFFAOYAV
SMILES
  • C1(=C(C(=O)C(=O)C(=O)C1=O)O)O
Properties
Chemical formula H2C6O6
Molar mass 170.076 g·mol
Appearance Orange to deep-red highly hygroscopic crystals
Melting point 130 to 132 °C (266 to 270 °F; 403 to 405 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). ☒N verify (what is  ?) Infobox references
Chemical compound

Rhodizonic acid is a chemical compound with formula H2C6O6 or (CO)4(COH)2. It can be seen as a twofold enol and fourfold ketone of cyclohexene, more precisely 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone.

Rhodizonic acid is usually obtained in the form of a dihydrate H2C6O6·2H2O. The latter is actually 2,3,5,5,6,6-hexahydroxycyclohex-2-ene-1,4-dione, where two of the original ketone groups are replaced by two pairs of geminal diols. The orange to deep-red and highly hygroscopic anhydrous acid can be obtained by low-pressure sublimation of the dihydrate.

Like many other enols, rhodizonic acid can lose the hydrogen cations H from the hydroxyls (pKa1 = 4.378±0.009, pKa2 = 4.652±0.014 at 25 °C), yielding the hydrogen rhodizonate anion HC6O−6 and the rhodizonate anion C6O2−6. The latter is aromatic and symmetric, as the double bond and the negative charges are delocalized and evenly distributed over the six CO units. Rhodizonates tend to have various shades of red, from yellowish to purplish.

Rhodizonic acid has been used in chemical assays for barium, lead, and other metals. In particular, the sodium rhodizonate test can be used to detect gunshot residue (which contains lead) in a subject's hands, and to distinguish arrow wounds from gunshot wounds for hunting regulation enforcement.

History

Rhodizonic acid was discovered by Austrian chemist Johann Heller in 1837, by analyzing the products of heating a mixture of potassium carbonate and charcoal. The name comes from Greek ῥοδίζω (rhodizō, "to tinge red"), on account of the color of its salts.

Chemistry

Salts

Rhodizonates tend to have various shades of red, from yellowish to purplish, in transmitted light, with a greenish luster in reflected light.

Potassium rhodizonate can be prepared with good yield and purity by oxidizing inositol with nitric acid and reacting the result with potassium acetate in the presence of oxygen. The rhodizonate crystallizes out of the solution due to its relative insolubility in water.

Sodium rhodizonate is dark brown and stable when dry, but the aqueous solution decomposes in a few days, even in the refrigerator. Lead rhodizonate is dark violet.

Oxidation and decomposition

Rhodizonic acid is a member of a chain of oxidation products: benzenehexol (COH)6, tetrahydroxybenzoquinone (THBQ) (COH)4(CO)2, rhodizonic acid (COH)2(CO)4, and the fleeting cyclohexanehexone (CO)6. Lithium rhodizonate, together with salts of THBQ and benzenehexol, has been considered for possible use in rechargeable electrical batteries. The monovalent anion C
6O
6 has been detected in mass spectrometry experiments.

Rhodizonic acid and the rhodizonate anion can lose one of the CO units to yield croconic acid (CO)3(COH)2 and the croconate anion C5O2−5, respectively, by mechanisms that are still imperfectly known. In basic solutions (pH > 10), rhodizonic acid quickly converts to the THBQ anion (CO)4−6 in the absence of oxygen, and to croconic acid in its presence. At pH 8.3 and exposure to light, solutions are stable for days in the absence of oxygen, and decompose to croconic acid and other products (possibly including cyclohexanehexone or dodecahydroxycyclohexane) in its presence.

Structure

Acid

In solution, the acid and the hydrogen rhodizonate ion are mostly hydrated, with some of the carbonyl groups >C=O replaced by geminal hydroxyls, >C(OH)2.

Salts

Lead Test Swab Containing Ampulized Rhodizonate
The sodium salt of rhodizonic acid is used in commercial lead testing kits

In anhydrous rubidium rhodizonate (Rb)2[C6O6], the rhodizonate anions are stacked in parallel columns, as are the rubidium ions. In the plane perpendicular to the columns, these are arranged as two interleaved hexagonal grids. The anions are planar.

Anhydrous potassium rhodizonate (K)2[C6O6] has a distinct but similar structure. The anions and cations are arranged in alternate planes. Within each plane, the anions are arranged in a hexagonal grid. Each potassium ion is arranged so that it connects symmetrically to eight oxygens of four anions, two from each adjacent plane. The anions are slightly twisted in the "boat" shape (with 0.108 Å of rms deviation from mean plane). Sodium rhodizonate (Na)2[C6O6] has the same structure, with slightly more distorted anions (0.113 Å rms)

In solution, the rhodizonate anion is not hydrated.

See also

References

  1. Patton, E.; West, R. (1970). "New aromatic anions. VIII. Acidity constants of rhodizonic acid". Journal of Physical Chemistry. 74 (12): 2512–2518. doi:10.1021/j100706a018.
  2. ^ Braga, D.; Cojazzi, G.; Maini, L.; Grepioni, F. (2001). "Reversible solid-state interconversion of rhodizonic acid H2C6O6 into H6C6O8 and the solid-state structure of the rhodizonate dianion C
    6O
    6 (aromatic or non-aromatic?)". New Journal of Chemistry. 25: 1221−1223. doi:10.1039/b107317f.
  3. ^ Gelb, R. I.; Schwartz, L. M.; Laufer, D. A. (1978). "The structure of aqueous rhodizonic acid". Journal of Physical Chemistry. 82 (18): 1985–1988. doi:10.1021/j100507a006.
  4. ^ Chalmers, R. A.; Telling, G. M. (1967). "A reassessment of rhodizonic acid as a qualitative reagent". Microchimica Acta. 55 (6): 1126–1135. doi:10.1007/BF01225955. S2CID 98540174.
  5. Di Maio, V. J. M. (1998). Gunshot Wounds: Practical aspects of firearms, ballistics, and forensic techniques (2nd ed.). CRC. p. 341. ISBN 0-8493-8163-0.
  6. Glover, R. L. (1981). "Detecting lead in "arrow" wounds in deer using rhodizonic acid". Wildlife Society Bulletin. 9 (3): 216–219. JSTOR 3781843.
  7. Heller, J. F. (1837). "Die Rhodizonsäure, eine aus den Produkten der Kaliumbereitung gewonnene neue Säure, und ihre chemischen Verhältnisse" [Rhodizonic acid, one of the new acids derived from potassium preparations, and its chemical composition]. Justus Liebigs Annalen der Pharmacie. 24 (1): 1–16. Retrieved 2009-07-08.
  8. Turner, E.; Gregory, W.; Parnell, E. A.; Liebig, J.; Rogers, J. B. (1846). Elements of Chemistry. Thomas, Cowperthwait & Co. Retrieved 2009-07-30. When potassium is heated in carbonic acid gas, combination takes place, and a dark olive powder is formed, composed of carbonic oxide and potassium, in the proportion C7O7+K3, or 7CO+3K. This substance is formed in large quantity in the preparation of potassium from carbonate of potash and charcoal, and is the source of great loss and inconvenience. No such compound is formed with sodium, for which reason that metal may be more cheaply prepared than potassium.
  9. Löwig, C. (1839). Chemie der organischen Verbindungen [Chemistry of Organic Compounds]. Zürich: F. Schultess.
  10. Hunter, R.; Morris, C., eds. (1900). Universal Dictionary of the English language. New York: Collier. Retrieved 2009-08-07.
  11. Preisler, P. W.; Berger, L. (1942). "Preparation of Tetrahydroxyquinone and Rhodizonic Acid Salts from the Product of the Oxidation of Inositol with Nitric Acid". Journal of the American Chemical Society. 64 (1): 67–69. doi:10.1021/ja01253a016.
  12. ^ Feigl, F.; Oesper, R. E. (1960). Spot Tests in Organic Analysis. Retrieved 2009-07-30.
  13. Gmelin, L.; Watts, H. (1856). Hand-book of Chemistry. Cavendish Society.
  14. Chen, H.; Armand, M.; Courty, M.; Jiang, M.; Grey, C. P.; Dolhem, F.; Tarascon, J.-M.; Poizot, P. (2009). "Lithium salt of tetrahydroxybenzoquinone: toward the development of a sustainable Li-ion battery". Journal of the American Chemical Society. 131 (25): 8984–8. doi:10.1021/ja9024897. PMID 19476355.
  15. Wyrwas, R. B.; Chick Jarrold, C. (2006). "Production of C
    6O
    6 from oligomerization of CO on molybdenum anions". Journal of the American Chemical Society. 128 (42): 13688–9. doi:10.1021/ja0643927. PMID 17044687.
  16. Iraci, G.; Back, M. H. (1988). "The photochemistry of the rhodizonate dianion in aqueous solution". Canadian Journal of Chemistry. 66 (5): 1293. doi:10.1139/v88-209.
  17. Zhao, B.; Back, M. H. (1991). "The photochemistry of the rhodizonate dianion in aqueous solution". Canadian Journal of Chemistry. 69 (3): 528. doi:10.1139/v91-079. Archived from the original on 2012-07-07. Retrieved 2009-08-07.
  18. Cowan, J. A.; Howard, J. A. K. (2004). "Dipotassium rhodizonate". Acta Crystallographica. E60 (4): m511–m513. doi:10.1107/S160053680400529X.
  19. Dinnebier, R. E.; Nuss, H.; Jansen, M. (2005). "Disodium rhodizonate: a powder diffraction study". Acta Crystallographica. E61 (10): m2148–m2150. doi:10.1107/S1600536805030552.
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