Names | |
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Preferred IUPAC name 5,6-Dihydroxycyclohex-5-ene-1,2,3,4-tetrone | |
Other names dihydroxydiquinoyl dioxydiquinone | |
Identifiers | |
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3D model (JSmol) | |
ChemSpider | |
ECHA InfoCard | 100.003.888 |
EC Number |
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MeSH | C005690 |
PubChem CID | |
CompTox Dashboard (EPA) | |
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Properties | |
H2C6O6 | |
Molar mass | 170.076 g·mol−1 |
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 [77 °F], 100 kPa). |
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. [1] [2]
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), [3] 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. [4] In particular, the sodium rhodizonate test can be used to detect gunshot residue (which contains lead) in a subject's hands, [5] and to distinguish arrow wounds from gunshot wounds for hunting regulation enforcement. [6]
Rhodizonic acid was discovered by Austrian chemist Johann Heller in 1837, by analyzing the products of heating a mixture of potassium carbonate and charcoal. [7] [8] [9] The name comes from Greek ῥοδίζω (rhodizō, "to tinge red"), [10] on account of the color of its 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. [11]
Sodium rhodizonate is dark brown and stable when dry, [12] but the aqueous solution decomposes in a few days, even in the refrigerator. [4] Lead rhodizonate is dark violet. [12] [13]
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 cyclohexanehexone (CO)6. [4] Lithium rhodizonate, together with salts of THBQ and benzenehexol, has been considered for possible use in rechargeable electrical batteries. [14] The monovalent anion C
6O−
6 has been detected in mass spectrometry experiments. [15]
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. [16] [17]
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. [3]
In anhydrous rubidium rhodizonate (Rb+)2[C6O6]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. [2]
Anhydrous potassium rhodizonate (K+)2[C6O6]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 "boat" shape (with 0.108 Å of rms deviation from mean plane). [18] Sodium rhodizonate (Na+)2[C6O6]2− has the same structure, with slightly more distorted anions (0.113 Å rms) [19]
In solution, the rhodizonate anion is not hydrated. [3]
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. The corresponding electrically neutral compound HO• is the hydroxyl radical. The corresponding covalently bound group –OH of atoms is the hydroxy group. Both the hydroxide ion and hydroxy group are nucleophiles and can act as catalysts in organic chemistry.
Perchloric acid is a mineral acid with the formula HClO4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but aqueous solutions up to approximately 70% by weight at room temperature are generally safe, only showing strong acid features and no oxidizing properties. Perchloric acid is useful for preparing perchlorate salts, especially ammonium perchlorate, an important rocket fuel component. Perchloric acid is dangerously corrosive and readily forms potentially explosive mixtures.
In chemistry, there are three definitions in common use of the word "base": Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rouelle in the mid-18th century.
Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl oxalate (C2O4(CH3)2). It is a conjugate base of oxalic acid. At neutral pH in aqueous solution, oxalic acid converts completely to oxalate.
In organic chemistry, a radical anion is a free radical species that carries a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a non-carbon radical anion is the superoxide anion, formed by transfer of one electron to an oxygen molecule. Radical anions are typically indicated by .
Sodium dithionite is a white crystalline powder with a sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions.
Squaric acid, also called quadratic acid because its four carbon atoms approximately form a square, is a diprotic organic acid with the chemical formula C4O2(OH)2.
The bisulfite ion (IUPAC-recommended nomenclature: hydrogensulfite) is the ion HSO−
3. Salts containing the HSO−
3 ion are also known as "sulfite lyes". Sodium bisulfite is used interchangeably with sodium metabisulfite (Na2S2O5). Sodium metabisulfite dissolves in water to give a solution of Na+HSO−
3.
Sodium metasilicate is the chemical substance with formula Na
2SiO
3, which is the main component of commercial sodium silicate solutions. It is an ionic compound consisting of sodium cations Na+
and the polymeric metasilicate anions [–SiO2−
3–]n. It is a colorless crystalline hygroscopic and deliquescent solid, soluble in water but not in alcohols.
Chloroauric acid is an inorganic compound with the chemical formula H[AuCl4]. It forms hydrates H[AuCl4]·nH2O. Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl4]− anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles.
Cyclohexanehexone, also known as hexaketocyclohexane and triquinoyl, is an organic compound with formula C6O6, the sixfold ketone of cyclohexane. It is an oxide of carbon, a hexamer of carbon monoxide.
Tetrahydroxy-1,4-benzoquinone, also called tetrahydroxy-p-benzoquinone, tetrahydroxybenzoquinone, or tetrahydroxyquinone, is an organic compound with formula C6O2(OH)4. Its molecular structure consists of a cyclohexadiene ring with four hydroxyl groups and two ketone groups in opposite (para) positions.
Deltic acid is a chemical substance with the chemical formula C3O(OH)2. It can be viewed as a ketone and double enol of cyclopropene. At room temperature, it is a stable white solid, soluble in diethyl ether, that decomposes between 140 °C and 180 °C, and reacts slowly with water.
Croconic acid is a chemical compound with formula C5H2O5 or (C=O)3(COH)2. It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms. It is sensitive to light, soluble in water and ethanol and forms yellow crystals that decompose at 212 °C.
A disulfite, commonly known as metabisulfite or pyrosulfite, is a chemical compound containing the ion S
2O2−
5. It is a colorless dianion that is primarily marketed in the form of sodium metabisulfite or potassium metabisulfite. When dissolved in water, these salts release the hydrogensulfite HSO−
3 anion. These salts act equivalently to sodium hydrogensulfite or potassium hydrogensulfite.
Croconate violet or 1,3-bis(dicyanomethylene)croconate is a divalent anion with chemical formula C
11N
4O2−
3 or ((N≡C−)2C=)2(C5O3)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion C
5O2−
5 through the replacement of two oxygen atoms by dicyanomethylene groups =C(−C≡N)2. Its systematic name is 3,5-bis(dicyanomethylene)-1,2,4-trionate. The term croconate violet as a dye name specifically refers to the dipotassium salt K
2C
11N
4O
3.
Croconate blue or 1,2,3-tris(dicyanomethylene)croconate is a divalent anion with chemical formula C
14N
6O2−
2 or ((N≡C−)2C=)3(C5O2)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion C
5O2−
5 through the replacement of three oxygen atoms by dicyanomethylene groups =C(−C≡N)2. The term Croconate Blue as a dye name specifically refers to the dipotassium salt K
2C
14N
6O
2.
A metaborate is a borate anion consisting of boron and oxygen, with empirical formula BO−2. Metaborate also refers to any salt or ester of such anion. Metaborate is one of the boron's oxyanions. Metaborates can be monomeric, oligomeric or polymeric.
Sulfoxylic acid (H2SO2) (also known as hyposulfurous acid or sulfur dihydroxide) is an unstable oxoacid of sulfur in an intermediate oxidation state between hydrogen sulfide and dithionous acid. It consists of two hydroxy groups attached to a sulfur atom. Sulfoxylic acid contains sulfur in an oxidation state of +2. Sulfur monoxide (SO) can be considered as a theoretical anhydride for sulfoxylic acid, but it is not actually known to react with water.
Technetium(IV) oxide, also known as technetium dioxide, is a chemical compound with the formula TcO2 which forms the dihydrate, TcO2·2H2O, which is also known as technetium(IV) hydroxide. It is a radioactive black solid which slowly oxidizes in air.
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.