9,10-Anthraquinones

Anthraquinones are yellow-brown pigments, most commonly occurring as 0-glycosides or C-glycosides. Their aglycones consist of two or more phenols linked by a quinone ring. Hydroxyl groups always occur at positions 1 and 8, that is, 1,8-dihydroxyanthraquinones. 

The main anthraquinone-containing plants are cascara sagrada Rhamnus purshiana), senna, rhubarb, aloes, dock and St John s wort. Rheum-emodin is a typical simple anthraquinone from rhubarb root Rheum palmatum). 

As anthraquinones are yellow-brown pigments many have been used historically as dyes for textiles, for example dyer s madder Rubia tinctoria). They are also known as anthracene glycosides, since anthracene was the first compound isolated, by French chemists Dumas and Lambert, in 1832. 

Experimental investigations with the most widely prescribed anthraquinones—sennosides A and B—show they pass through the stomach and small intestine unaltered, but that in the caecum and colon they are converted to dianthrones (their aglycones) by microorganisms. The dianthrones, which remain unabsorbed, are further transformed into anthrone and anthraquinone, producing hydra-gogue and laxative effects in the process (Adzet and Camarasa 1988). 

The laxative effect is thought to occur as a result of increased peristaltic action and inhibition of water and electrolyte resorption by the intestinal mucosa. There is no evidence of direct irritation of the bowel mucosa (Bruneton 1995). 

3 Anthraquinones. - Murugesan and colleagues have investigated the effects of substituents on the photochemical properties of these compounds, many of which are anti-tumour agents. Cynodontin and a methoxylated derivative were shown to generate both 02 and 02 upon irradiation in the 300-700 nm region. 

The field dependencies of the electron mobility of vapor-deposited DCAQ. 

PS and PC. These agree with values reported for a wide range of acceptor and donor doped polymers (Borsenberger et al., 1993). 

Borseriberger et al. (1994b) measured electron mobilities of vapor-deposited 2-methyl-2-pentyl-l,3-bis(dicyanomethylene)indane (DCMI). DCMI is a highly polar acceptor molecule with a dipole moment of 3.9 Debye. At high fields, the field dependencies were described as log/r At low fields, the mobilities 

This differs from the expression for T TC in that the constant in the exponent is 1/2, rather than 2/3. Describing the T TC data in Fig. 14 by Eq. (3) yields a = 0.110 eV, in excellent agreement with the value of 0.112 eV derived from the T TC data. Borsenberger et al. described the width of the DOS by the dipolar disorder model and concluded that the width was largely determined by the dipolar component. 

Rommens et al. (1995) measured hole mobilities of l,3-di(dicyano-methylene)-2-allyl-2-methylindane (ADCMI) doped PC. The dipole moment of ADCMI is 3.9 Debye, the same as DCMI. Mobilities were determined from transit times derived by the method described by Scott et al. (1992). Over a wide range of fields, temperatures, and concentrations, the field dependencies 

There is a wide diversity of chemical structures of anthraquinone colorants. Many anthraquinone dyes are found in nature, perhaps the best known being alizarin, 1,2-dihydroxyanthraquinone, the principal constituent of madder (see Chapter 1). These natural anthraquinone dyes are no longer of significant commercial importance. Many of the current commercial range of synthetic anthraquinone dyes are simply substituted derivatives of the anthraquinone system. For example, a number of the most important red and blue disperse dyes for application to polyester fibres are simple non-ionic anthraquinone molecules, containing substituents such as amino, hydroxy and methoxy, and a number of sul-fonated derivatives are commonly used as acid dyes for wool. 

Anthraquinone (52) is only weakly coloured, its strongest absorption being in the UY region (2max 325 nm). The UY/visible spectral data for a series of substituted anthraquinones, 52a-h, are given in Table 4.1 and these illustrate the effect of the substituent pattern on the colour. The introduction of simple electron-releasing groups, commonly amino or 

Indigo (57), the parent system of this group of colorants, is one of the oldest known natural dyes (see Chapter 1). The naturally occurring 

A question which has intrigued colour chemists for years is why indigo, a relatively small molecule, absorbs at such long wavelengths. The colour of indigo depends crucially on its environment. It is known that, in the vapour phase, the only situation in which it approaches a monomolecular state, indigo is red. In solution, indigo exhibits pronounced positive solvatochromism in non-polar solvents it is violet, while in polar solvents it is blue. In the solid state, and when applied to fabric as a vat dye, it is 

Bisantrene (56), also known as orange crush , is a broad spectrum intercalating antitumor agent competing with doxorubicin and the somewhat more closely related quinone mitoxantrone (51) 

Polycyclic Aromatic Compounds and Their Reduction Products 

The synthesis of bisantrene begins with Diels-Alder reaction of anthracene (52) and ethylene 

This readily forms a bis-hydrazone with guanylhydrazine [16]. 

Anthraquinone groups are highly photoreactive by exposure to long UV light ranging from 340 to 360 nm. Unlike photoreactive groups that form intermediate nitrene or carbine precursors 

Averantin (154) and 6-0-methylaverantin (155) have been isolated from the lichen Solorina crocea 306). Although averantin was originally isolated from fungi 16), 6-0-methylaverantin is a novel metabolite. 

Mishchenko and coworkers 240) have isolated the known fungal metabolites islandicin (156) and cynodontin (157) from a lichen species, Asahinea chrysantha, for the first time. In addition two new metabolites, 4-hydroxyemodin (158) and 4,5-dihydroxyemodin (159) were isolated from this lichen. The assigned structure (of 4-hydroxyemodin) of the new anthraquinone was untenable since the natural compound was found to differ from synthetic 4-hydroxyemodin. 

In 1907 Zopf (764) isolated from the lichen Cladonia bellidiflora a red-brown crystalline compound which he named bellidiflorin. More than 80 years later Alagna et al. (7) showed by X-ray crystallography that bellidiflorin is an iron complex of the 6/3-anthraquinone gracili-formin (186) the coordination of the ligands to the iron atom is shown in Fig. 10. 

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Dissolves in alkaline solutions to give purple-red solutions which are precipitated as lakes by heavy metal salts. Occurs naturally as a glucoside in madder but produced synthetically by fusing anthraquinone-2-sulphonic acid with NaOH and some KCIO3. Applied to the mordanted fibre. Al(OH)3 gives a bright red lake, Cr(OH)3 a red lake, FefOH) ... 

C. A typical aromatic amine. Best prepared by the prolonged action of concentrated ammonia solution at a high temperature upon anthraquinone-l-sulphonic acid in the presence of BaClj and by reduction of the corresponding nitro compound or by amination of the chloroanthraquinone. 

Of little use commercially except as a route to anthraquinone. For this purpose it is oxidized with acid potassium dichromate solution, or better, by a catalytic air oxidation at 180-280 C, using vanadates or other metal oxide catalysts. 

It is an important dyestuffs intermediate. It condenses with chloroethanoic acid to give phenylglycine-o-carboxylic acid for the synthesis of indigo. It can be diazotized and used as a first component in azo-dyes it condenses also with chloroanthraquinones to give intermediates for anthraquinone dyes. 

It is prepared by acidifying an alkali solution of anthrone or by reduction of anthraquinone with aluminium powder and concentrated sulphuric acid. 

Reduction of anthraquinone gives dianthryl, anthrone and finally anthracene. 

It has been used as a bird repellant and is the parent compound of the anthraquinone vat dyes in which the dyeing is carried out by immersion in the reduced vat solution followed by air oxidation to the original insoluble compound. 

Anthraquinone can be brominated, chlorinated directly to the tetrachloro (I, 4, 5, 8-) stage, nitrated easily in the 1-position, but gives the 1,5-and 1,8-dinitro-derivalives on prolonged nitration the nitro groups in these compounds are easily displaced by neutral solutions of alkali sulphites yielding the corresponding sulphonic acids. Sulphonation with 20-30 % oleum gives the 2- 2,6- and 2,7-derivatives in the presence of Hg the 1- 1,5- and 1,8- derivatives are formed. 

Anthraquinone-J -sulphonic acid. Colourless leaflets, m.p. 214 C. It is used in the preparation of l-aminoanthraquinone. 

Fieser s solution An aqueous alkaline solution of sodium anthraquinone -sulphonale (silver salt) reduced with sodium dithionite, Na2S204, and used as a scrubbing solution for partially removing O2 from, e.g., N2. 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

The above method has now been largely replaced by a newer process, in which the substance 2-ethylanthraquinone is reduced by hydrogen in presence of a catalyst to 2-ethylanthraquinol when this substance is oxidised by air, hydrogen peroxide is formed and the original anthraquinone is recovered ... 

Compounds containing olefine links may be oxidised to 1,2-diketones, as in C4H CH CHC Hs -> C HjCO-COC H. Anthracene is readily oxidised to anthraquinone, but phenanthrene is almost unaffected. 

Anthracene is oxidised by chromium trioxide, Cr04, to anthraquinone. As the reaction is carried out in solution, a solvent is required which will dissolve both the anthracene and the chromium trioxide, and at the same time be... 

Recrystallise the remaining half of the crude anthraquinone from boiling acetic acid, using animal charcoal filter the hot solution through a Buchner funnel which has been preheated by the filtration of some of the boiling solvent, as the anthraquinone crystallises rapidly as the solution cools. Cool the filtrate in cold water and then filter at the pump, drain, wash with methylated spirit and dry. Yield, 4-5 g. 

Dissolve 1 g. of anthracene in 10 ml. of glacial acetic acid and place in 50 ml. bolt head flask fitted with a reflux water-condenser. Dissolve 2 g. of chromium trioxide in 2 ml. of water and add 5 ml. of glacial acetic acid. Pour this solution down the condenser, shake the contents of the flask and boil gently for 10 minutes. Cool and pour the contents of the flask into about 20 ml. of cold water. Filter off the crude anthraquinone at the pump, wash with water, drain well and dry. Yield, 1 g. Purify by re crystallisation from glacial acetic acid or by sublimation using the semi-micro sublimation apparatus (Fig. 35, p. 62, or Fig. 50, p. 70). 

Anthraquinone is of great technical importance, as many of its derivatives form valuable dyes notable among these are the hydroxy-derivatives (alizarin, etc.)y the amino-derivatives (indanthrene, etc.) and the sulphonic acids. 

Benzoquinone, p-toluquinone, 1 2-naphthoquinone,, naphthoquinone, anthraquinone,, io-phenanthraquinone, alizarin. 

Anthraquinone and alizarin are unaffected by sulphurous acid. Phenanthraquinone is reduced in warm ethanolic solution by SO2 water to hydrophenanthraquinone, m.p. 147°. 1,2-Naphthoquinone gives the corresponding hydronaphthoquinone, m.p. 60°. Toluquinone gives toluhydroquinone, m.p. 124 . 

Anthraquinone does not liberate iodine from KI solution. 

Alizarin dissolves in aqueous NaOH solution giving a purple solu tion. Calcium hydroxide will precipitate a blue sdt from this solution. Anthraquinone is unaffected by NaOH solution. 

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