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|Section2= |Section3= }} Rhodizonic acid is a chemical compound with formula C6H2O6 or (CO)4(COH)2. It can be seen as a two-fold enol and four-fold 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 colorless "dihydrate" C6H2O6·2H2O. 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 hydroxyls. The orange to deep-red and highly hygroscopic anhydrous acid can be obtained by low-pressure sublimation of the dihydrate.〔 Elizabeth Patton, Robert West (1970), ''New aromatic anions. VIII. Acidity constants of rhodizonic acid''. J. Phys. Chem., volume 74 issue 12, pp 2512–2518. 〕〔 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. 〕 Like many other enols, rhodizonic acid can lose the hydrogen cations H+ from the hydroxyls (pK1 = 4.378 ± 0.009, pK2 = 4.652 ± 0.014 at 25 °C),〔 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. 〕 yielding the hydrogenrhodizonate anion C6HO6− and the rhodizonate anion C6O62−. 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.〔 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. 〕 In particular, the sodium rhodizonate test can be used to detect gunshot residue (which contains lead) in a subject's hands,〔 Vincent J. M. Di Maio, ''Gunshot wounds: practical aspects of firearms, ballistics, and forensic techniques, 2nd edition. CRC, 1998. ISBN 0-8493-8163-0. p. 341. 〕 and to distinguish arrow wounds from gunshot wounds for hunting regulation enforcement.〔 Ronald L. Glover (1981), ''Detecting Lead in "Arrow" Wounds in Deer Using Rhodizonic Acid'' Wildlife Society Bulletin, Vol. 9, No. 3, pp. 216-219. (Online version ) accessed on 2009-07-30. 〕 ==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.〔 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. (Online version ) accessed on 2009-07-08. 〕〔 Edward Turner, William Gregory, Edward Andrew Parnell, Justus Liebig, James Blythe Rogers (1846), ''Elements of chemistry''. Thomas, Cowperthwait & Co. (Online version ) 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 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." 〕〔 Carl Löwig (1839), ''Chemie der organischen Verbindungen''. F. Schultess, Zürich. 〕 For a while, rhodizonates were believed to have the formula C7O7 · Me3.〔 Carl Löwig, Daniel Breed ''Principles of organic and physiological chemistry''. (Online version ) accessed on 2009-07-30. 〕 The name comes from Greek ''ῥοδίζω'' (''rhodizō'', "to tinge red"),〔 Robert Hunter and Charles Morris (1900), ''Universal dictionary of the English language''. Collier, NY. (Online version ) accessed on 2009-08-07. 〕 on account of the color of its salts. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「rhodizonic acid」の詳細全文を読む スポンサード リンク
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