Rhodizonic acid

Rhodizonic acid sodium salt (5,6-dihydroxycyclohex-5-ene-l,2,3,4-tetraone di-Na salt)... 

The four-, five-, and six-membered analogs (178,180, and 182) were also obtained from the diprotonation of squaric acid (3,4-dihydroxy-3-cyclobutene-l,2-dione, 177), tri-O-protonation of croconic acid (4,5-dihydroxy-4-cyclopentene-l,2,3-trione, 179), and tetra-O-protonated rhodizonic acid (5,6-dihydroxy-5-cyclohexene-l,2,3,4-tetraone, 181), respectively. These ions were prepared in either Magic Acid (1 1 FSOsH-SbFs) or fluorosulfuric acid at low temperature and characterized by NMR. Ab initio/IGLO calculations showed that di-O-protonated squaric acid (178) is planar and aromatic, whereas the polyprotonated croconic and rhodizonic acids (180 and 182) have more carboxonium ion character, and no indication was obtained for any significant contributing homoaromatic structures. 

Derivatives. A considerable number of compounds that contain the benzenehexol structure possess therapeutic activity. Esterification of benzenehexol with a pyridinecarbonyl chloride gives the corresponding hexaesters, which are antiatherogenics (267). Tetroquinone [319-89-1] (tetxahydroxy-/>-benzoquinone) is administered orally for the treatment of keloids. The dipotassium salt of rhodizonic acid (80) is useful as a remedy for diabetes mellitus (262). Compounds, eg (81) and (82), which are derived from rhodizonic acid, are useful as antiinflammatory agents and diuretics (qv) (268). 

Deltic acid Squaric acid Croconic acid Rhodizonic acid Tropolone... 

Carbon-13 NMR spectra of the H2C On series, such as deltic, squaric, croconic and rhodizonic acids, obtained in anhydrous solvents [304] display carbonyl shifts similar to those reported for quinones (Table 4.33). Considerable shielding of the carbonyl carbon of deltic acid diethyl ester is not only attributed to the three-membered ring but also to an electron releasing effect of the ethoxy groups. 

As shown above, di-tert-butoxyethyne 1s the only acetylenic diether prepared so far whose stability allows its use as a synthetic Intermediate. It has been used 1n the synthesis of all the members of the series of monocyclic oxocarbons (deltic, squaric, croconic, and rhodizonic acids), as well as in the synthesis of semisquaric acid, the parent compound of the natural mycotoxins, noniliforndna... 

H. S. Isbell, H. L. Frush, and Z. Orhanovic, Oxidation of sodium salts of alduronic and glyculosonic acids by sodium peroxide, Carbohydr. Res., 36 (1974) 283-291 Oxidation of certain cyclic carbonyl compounds with alkaline hydrogen peroxide, ibid., 43 (1975) 93-100 H. S. Isbell, Concurrent oxidation and reduction reactions of cyclohexanehexone, rhodizonic acid, and tetrahydroxy-l,4-benzoquinone with hydrogen peroxide, ibid., 39 (1975) C4-C7. 

The hydrogenation of rhodizonic acid 1,4-diimine and triaminophloro-glucinol has been reported to give 50% yields of an inosadiamine and an inosatriamine, respectively.233 No information about the configurations of the products has been published. 

Group IIA. Hg, Pb, Bi, Cu, and Cd The metals are present as chlorides in dilute hydrochloric acid. The solvent used is n-butyl alcohol saturated with 3m hydrochloric acid. To obtain a good separation of copper and lead, the strip should be at least 45 cm long. The solvent is allowed to flow for 15-18 hours in an atmosphere saturated with respect to both organic solvent and aqueous phases. After evaporation of the solvent, the strip is sprayed with a solution of dithizone in chloroform (0 05 per cent w/v). Lead gives only a weak colour with dithizone and is best detected by spraying the top portion of the strip with an aqueous solution of rhodizonic acid. 

Sodium rhodizonate (0-5 %). Dissolve 0-5 g sodium rhodizonate (rhodizonic acid, sodium salt C6OeNa2) in 100 ml water. The solution decomposes rapidly. 

The crystal structures of three metal rhodizonato complexes were determined Rb2Cg Oe , prepared by reacting anhydrous rhodizonic acid with RbOH, and the other two , 108, prepared by reacting aqueous Na2C60e, with 2,2 -bipyrimidine and either Cd(N03)2 4H2O or MnCl2. 

It was Maquenne" who first threw light on the structure of inositol by showing that violent treatment with hydriodic acid gave recognizable quantities of benzene, phenol and triiodophenol." Oxidation with concentrated nitric acid at 100° gave tetrahydroxy-p-benzoquinone and rhodizonic acid, further demonstrating the presence of a six-carbon cycle. ... 

In recent years the salts of tetrahydroxy-p-benzoquinone and rhodizonic acid have found considerable use as indicators in the volumetric determination of sulfates with barium salt solution. In this connection, F. A. Hoglan and E. Bartow, J. Am. Chem. Soc., 62, 2397 (1940), have studied the nitric acid oxidation of inositol, and P. W. Preisler and L. Berger, J. Am. Chem. Soc., 64, 67 (1942), have developed methods for preparing pure salts of tetrahydroxy-p-benzoquinone and rhodizonic acid from inositol. 

By condensing the sodium salt of rhodizonic acid with o-phenylenedi-amine a quinone was obtained as early as 1888, but the originally proposed structure as a 2,3-dione (1888CB1227) was shown to be incorrect, the compound being in fact 295 (62LA131). 

Deprotonation of rhodizonic acid (132) produces a dianion (133) which possesses aromatic character. Photolysis of this dianion in aqueous solution containing electron acceptors is found to yield croconate dianion (134), and the quantum yield of the reaction has been measured for various concentrations of the acceptors. The mechanism of the reaction is uncertain but may involve ring contraction following electron transfer and addition of water. 

It has often been assumed that any cyclitol having two cts-l,2-diol structures will react with acetone to give a diacetal. However, the dinitro-tetrol (106) affords only a monoacetal, for steric reasons. b. Diaminocyclohexanetetrols.— The dinitrotetrol (106), on reduction, gave the corresponding diaminotetrol. The conversion of dibromotetrols into diaminotetrols has been mentioned. Other methods include the reduction of a nitroaminotetrol derivative and of rhodizonic acid diimine (108). ... 

Acid solvolysis of cycloadduct 83 with trifluoroacetic acid affords a quantitative yield of hexahydroxybenzene, which is an important precursor in the synthesis of rhodizonic acid... 

With oxygen, carbon forms two well-marked gaseous compounds, which shall be here described. The same elements, in other proportions, constitute, according to the opinion which regai ds oxygen acids as hydrates, certain anhydrous acids, to be described under the head of organic chemistry. As these anhydrous acids, however, are not known in the separate form, we may rather consider the acids in question (the oxalic, mel-litic, croconic, and rhodizonic acids) as compounds of hydrogen. 

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