Anthrones, reactions with

General color reactions of this type include the Molisch test with a-naphtfiol and concentrated sulfuric acid and the anthrone reaction with anthrone and sulfuric acid. The latter is used for quantitive colorimetric determinations. Reaction conditions can be chosen so that only ketoses react (HCl - - resorcinol, Seliwanoff s test) or only pentoses (HCl -b orcinol. Rial s test). These reactions help to distinguish the various sugars. 

The methylene group of anthrone 64 is acidic by virtue of doubly vinylic activation by the carbonyl group. Thus, treatment with methyl iodide and base leads to the 9,9-dimethyl derivative 65. Grignard reaction with 6-dimethylaminopropyl magnesium chloride... 

Benzanthrone, in turn, is obtained from anthraquinone by reaction with glycerine and sulfuric acid in the presence of a reducing agent such as iron. Anthraquinone is initially reduced to anthrone, which is condensed with acrolein. Acrolein, on the other hand, is an intermediate of the reaction between glycerine and sulfu-... 

D-glucose, and 5-(hydroxymethyl)-2-furaldehyde with anthrone lends support to these conclusions, and further indicates the complexity of the overall reaction. In the reaction of either D-fructose or 5-(hy-droxymethyl)-2-furaldehyde with anthrone, at least nine compounds were observed, three of which were condensation products of anthrone itself. The other products had absorption maxima ranging from 490 to 770 nm (in sulfuric acid solution and under the conditions of the anthrone reaction). One of the prominent pigments, having a blue color ( max 620 nm) and a postulated structure corresponding to compound 123, was isolated and characterized by its nuclear magnetic... 

Photostimulated, S r k 1 reactions of carbanion nucleophiles in DMSO have been used to advantage in C—C bond formation (Scheme 1).25-27 Thus, good yields of substitution products have been obtained from neopentyl iodide on reaction with enolates of acetophenone and anthrone, but not with the conjugate base of acetone or nitromethane (unless used in conjunction, whereby the former acts as an entrainment agent).25 1,3-Diiodoadamantane forms an intermediate 1-iodo mono substitution product on reaction with potassium enolates of acetophenone and pinacolone and with the anion of nitromethane subsequent fragmentation of the intermediate gives derivatives of 7-methylidenebicyclo[3.3.1]nonene. Reactions of 1,3-dibromo- and 1-bromo-3-chloro-adamantane are less effective.26... 

The intervention of a radical process has been suggested to account for the anomalous reaction with anthrone, leading to exchange of hydrogen for fluorine rather than attack at the carbonyl group [193] (Figure 3.38). 

Except for the formic acid extraction, < all the other methods yielded approximately the same amount of polysaccharide. However, even after more than 20 successive extractions of a Swiss brown-earth (Braunerde) with acid, water, and alkali, further extracts gave a positive anthrone reaction for sugars. " The extraction of polysaccharides is probably made difficult by their interaction with inorganic surfaces and humic substances. 

Another silanization procedure for the derivatization of carbohydrates is the formation of trimethylsilyl oximes. The methyloxime is heated with hexarnethyl-disilazane trifluoroacetic anhydride (9 1 v/v) for 1 h at 100°C. Anthrone O-glucoside is an important ingredient in skin care cosmetics and can be fully silylated by reaction with A/,0-bistrimethylsilylacetamide acetonitrile mixture (1 1 v/v) for 1 h at 90°C, and subsequently separated by GC. 

The cycloaddition is ascribable to the oxyanion of hydrogen-bonded enolate (ArO —HNEt3 ) rather than to the hydrogen-bonded enol (ArOH—NEtj). An enantioselective version of the reaction was achieved by using a homochiral amine [27]. Similarly the reactions with less reactive dienophiles such as dimethyl fumarate, fumaronitrile, maleonitrile and methyl acrylate give the Diels-Alder adducts quantitatively when the cycloadditions are carried out in THF or CHCI3 in the presence of EtjN, while in MeOH Michael adducts were isolated. Experimental evidence supports the hypothesis that the base-catalyzed cycloadditions of anthrone with dienophiles are concerted Diels-Alder processes [25b]. 

Phthalic anhydride undergoes Friedel-Crafts reaction with benzene to yield ortho-henzoyl benzoic acid, which gets cyclized to anthraquinone, and it gets reduced to produce anthrone . Explain the sequence of reactions involved briefly. 

It may be possible that the anthrone undergoes the Michael Reaction with acrolein, and the cyclized product is then oxidized by anthraquinone and the latter is reduced to anthrone, as shown by the partial illustration of the mechanism. This route is consistent with the relatively low yield of 50-60% ... 

The glycosidic bond of glycolipids is readily hydrolyzed by acid, and the carbohydrates liberated can be analyzed by instrumental methods, e.g., gas chromatography (GC), liquid chromatography (LC), or colorimetric procedures can be used. In one colorimetric procedure, the total amount of hexose units in a glycolipid can be quantified by reaction with anthrone in concentrated sulfuric acid and determination by the absorbance at 635 nm. 

Anthrones [204] and 3-substituted oxindoles [205] possess activated methylenes which have been able to react under asymmetric iminium catalysis with a,p-unsaturated aldehydes. The reaction with 3-substituted oxindoles is especially attractive, since chiral quaternary stereocenters are generated. For this purpose, chiral primary amine thiourea catalyst 132 has been demonstrated as a very efficient promoter for the addition of 3-alkyl substituted oxindoles to P-aryl substituted enals in the presence of benzoic acid as cocatalyst in toluene at rt to afford the corresponding Michael adducts in good diastereoselectivities (dr up to >19/1) and good enantioselectivities (73-93% ee) (Scheme 2.75) [205a], P-Alkyl substituted enals are not suitable partners for the reaction affording very low diastereo- and enanti-... 

Several other methods of polymer quantification in biological material have been used. In general, a polymer is usually isolated from biological material by a deproteini-zation procedure, extraction with organic solvents, etc., and then analyzed. Elemental analysis, viscosimetryturbidimetryand complexation with iodine (for PVP) in extracts were used in early studies in this field. These methods are now rarely used and have been replaced by labelling methods. Among the classical analytical techniques, the anthrone reaction for the estimation of carbohydrate polymers (e.g. dextran inulin >) has remained useful. 

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