Reduction of anthraquinone

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. 

Reduction of anthraquinone with tin and concentrated hydrochloric acid in the presence of boiling glacial eicetic acid gives anthrone this substance (keto form) under certain conditions passes into the enol form, anthranol ... 

Depending on experimental conditions, sodium borohydride reduction of anthraquinone, in a lower ahphatic alcohol, results in 9,10-dihydroxyanthracene... 

An example of industrial interest is the benzanthrone (9) synthesis. Benzan-throne derivatives are manufactured by cathodically reducing anthraquinone derivatives that may contain electronegative substituents [61]. In the cathode compartment the reduction of anthraquinone (7) in 85% H2S04 to oxanthrone (8) occurs which in presence of glycerol reacts to form benzanthrone (9), which is an important dye intermediate [40, 61]. 

Benzanthrone (6.73) is the source of various commercially important violet, blue and green vat dyes. This tetracyclic system can be prepared from a mixture of anthraquinone and propane-1,2,3-triol (glycerol) by heating with iron powder in concentrated sulphuric acid. The reaction involves reduction of anthraquinone to anthrone (6.74) followed by condensation (Scheme 6.14) with propenal (acrolein), the latter compound being generated... 

More reliable reagents for the preparation of sulfinic acids are zinc [694, 695], sodium sulfide [249] and sodium sulfite [2S2. These reagents not only stop the reduction at the stage of the sulfinic acids (in the form of their salts) but do not reduce other functions present in the molecules. In the reduction of anthraquinone-l,5-disulfonyl chloride with sodium sulfide below 40° anthraquinone-l,5-disulfinic acid was obtained in 83.5% yield [249], and p-cyanobenzenesulfonyl chloride was reduced to p-cyanobenzenesulfinic acid in 87.4% yield [252]. 

The most important method of making hydrogen peroxide is by reduction of anthraquinone to the hydroquinone, followed by reoxidation to anthraquinone by oxygen and formation of the peroxide. R is usually ethyl but /-butyl and jec-amyl have also been used. 

The reduction of anthraquinone differed from that of benzoquinone in that small increments of the substrate were catalytically reduced (H/substrate = 2.0) even in the absence of added alkali. It would appear that the initial complex formed in this case either is spontaneously hydrolyzed or interacts with the excess CoH present. 

LI The Anthraquinone Actinometer. The first example is the photo reduction of anthraquinone in ethanol (Figure 7.41). 

The anthraquinones may be reduced to the corresponding anthra-quinols (hydroxyanthranols) with alkaline sodium hydrosulphite this reaction has a wide application in the dye industry. These compounds are difficult to isolate pure, for they rapidly oxidise in air. The anthranols —y-monohydroxyanthracenes—however, are stable, and may be obtained by reducing anthraquinone with acid-reducing agents—tin and hydrochloric acid, zinc and glacial acetic acid, copper or aluminium, and sulphuric acid, etc. For the complete reduction of anthraquinone, see Reaction LYIII. (a). 

Quinones of the more reactive, polycyclic, aromatic systems can usually be obtained by direct oxidation, which is best carried out with chromium(vi) compounds under acidic conditions. In this way 1,4-naphthoquinone, 9,10-anthraquinone and 9,10-phenanthraquinone are prepared from naphthalene, anthracene and phenanthrene respectively (Expt 6.128). Also included in this section is the reduction of anthraquinone with tin and acid to give anthrone, probably by the sequence of steps formulated below. 

Equation (6.41) for the current-potential response has been applied to the analysis of different experimental systems of interest. For example, the experimental SCV voltammograms of the two-electron reduction of anthraquinone-2-sulfonate (AQ) in different mixtures of alkylammonium salts obtained at a gold macroelectrode (radius = 0.9mm) with a scan rate v = lOOmVs 1 are shown in Fig. 6.3 when a staircase... 

Baughman (1992) measured the disappearance rate constants for a number of solvent and disperse azo, anthraquinone, and quinoline dyes in anaerobic sediments. The half-lives ranged from 0.1 to 140 days. Product studies of the azo dyes showed that reduction of the azo linkages and nitro groups resulted in the formation of substituted anilines. The 1,4-diaminoanthraquinone dyes underwent complex reactions thought to involve reduction and replacement of amino with hydroxy groups. Demethylation of methoxyanthraquinone dyes and reduction of anthraquinone dyes to anthrones also was observed. 

Similarly, phenothiazine may be oxidized to the cation radical species which then dimerizes forming the 3,10 -diphenothiazinyl species (Tsujino, 1969). The product of the electron-transfer step may react, via a second-order process, with a species in solution to form a new product. An example of this type of mechanism involves the reduction of anthraquinone and its derivatives in the presence of oxygen (Jeziorek etal., 1997). To understand quantitatively an EC and EC2 process, the concentration and scan-rate dependence of the associated cyclic voltammograms is matched with theory deriving from the mass transport/kinetic equations for each species. 

Figure 27. Application of flow cell and UV spectroscopy to study the reduction of aromatic compounds in iV,iV-dimethylformamide/0.1 M BU4NBF4 a) Plot of absorbance at = 556 nm and 732 nm, of the products obtained in the reduction of anthraquinone (T) and anthracene ( ), respectively, as the galvanostatic current to the flow cell is increased and a continuous flow of 5 mL min is maintained. The substrate concentrations are both 0.1 mM and the light path is 1 cm b) and c) The absorption spectra of the product obtained from reduction of anthraquinone and anthracene, respectively, when the galvanostatic current is increased above the maximum required for generating the radical anion. The current is increased from 2.0 to 2.8 mA in steps of 0.2 mA and the development in the spectra is indicated with arrows. Isosbestic points are also indicated. For anthraquinone, the spectra of the radical anion and the dianion could be resolved whereas for anthracene the dianion is protonated and spectra of the radical anion and 9,10-dihydroanthracen-9-ide could be resolved [65].

Reduction of anthraquinone to anthrone can be accomplished rapidly on a small scale with tin(II) chloride in acetic acid solution. A second... 

B. Keita, I. Kawenoki, J. Kossanyi, and L. Nadjo, Reduction of anthraquinone derivatives at n-type and p-type silicon electrodes, J. Electroanal. Chem. 145, 311, 1983. 

In the classical student preparation of aniline - granular tin and hydrochloric acid is just as satisfactory as the more expensive stannous chloride because the product is isolated, after alkalinization, by steam distillation. However, for reduction of anthraquinone to anthrone the SnCU-HCl-AcOH method (see Stannous chloride) seems preferable to the Sn-HCl-AcOH method because it eliminates a troublesome filtration of the hot acid solution and because the yield is 10% better. In those cases where the metal alone has been used it is not clear whether the chloride was tried and found unsatisfactory or merely not tried. A procedure for the reduction of anisoin to desoxyanisoin specifies use of 200-mesh tin in 40% excess of the theory, and a note states that reduction in the amount of metal reduces the yield. 

Derivation Reduction of anthraquinone with tin and hydrochloric acid. 

There are a number of different reactions which can occur during the reduction of anthraquinone or indanthrone vat dyes. The indanthrones can be reduced at two carbonyl groups, which, in this particular case, is desir-... 

Selective reductions. Brown et al.2 conducted an extensive study of reductions with diborane in THF. Most aldehydes and ketones are readily reduced unusually high stereoselectivity was realized in the case of norcamphor, which was reduced to 98% endo-norbornanol and 2% exo-norbornanol. p-Benzoquinone is reduced to hydroquinone at a moderate rate, but reduction of anthraquinone is sluggish. Carboxylic acids are reduced very rapidly indeed this group can be reduced selectively in the presence of many other substituents. Acid chlorides react much more slowly than carboxylic acids. Esters and ketones are reduced relatively slowly. Reactions with epoxides are relatively slow and complex. 

This NADP regeneration consists of the three consecutive Reactions [31a]-[31c]. The reduction of anthraquinone-2,6-disulphonate at the expense of NAD(P)H catalysed from AMAPORs in form of crude cell extract of C. thermoaceticum, the reoxidation of the reduced mediator in a spontaneous reaction with oxygen (112) and the splitting of the hydrogen peroxide by catalase. 

Sodium hydrosulfite (hyposulfite), Na2S204, in alkaline solutions has come to play an important part in the reduction of anthraquinone and in-digoid derivatives to the leuco compounds. Although it is an active reducing agent, it finds only a limited use in the reduction of nitro compounds because of its comparatively greater cost. 

Depending on experimental conditions, sodium boioliydride reduction of anthraquinone, in a lower aliphatic alcohol, results in 9,10-dihydroxyanthracene (3) [4981-662] 9,lO-dihydro-9,10-dihydroxy-anthracene (4) [70143-55-4] anthrone (5) [90 14-8], and anthrol (6) [529-86-2] (12) ... 

Baughman, G. L., E. J. Weber and M. S. Brewer. 1992. Sediment reduction of anthraquinone dyes and related compounds anthrone formation. Presented at the American Chemical Symposium on the Oxidation-Reduction Transformations of Inorganic and Organic Species in the Environment, San Francisco, CA, April 5-10, 1992. 

It is generally accepted that this reaction involves the conversion of glycerol into acrolein and reduction of anthraquinone to anthrone, the latter undergoing the Aldol Condensation with acrolein. After that, the consecutive dehydration, cyclization, and oxidation afford the final product of benzanthrone. An illustration of the reaction mechanism is displayed here. 

Liebermann discovered the reaction between nitrous acid and phenols and secondary amines named after him. He prepared amino-naphthols from nitro-naphthols, synthesised the dihydroxyanthraquinones anthrarufin and chrysazin, and studied the reduction of anthraquinone. Another dihydroxy-anthraquinone, quinizarin, was discovered by F. Grimm by heating hydro-quinone with phthalic anhydride. 

For the determination of anthraquinone, added as a stabilizer in capacitor dielectrics (using chlorinated diphenyls, chlorinated naphthalenes and mineral oils as impregnants) a solvent consisting of a 3 2 mixture of chloroform and methanol with magnesium chloride and hydrochloric acid was able to dissolve all materials used.< ) Owing to the presence of the strong acid, the reduction of anthraquinone is shifted to potentials near 0 0 V. At these potentials the waves of the chlorinated products do not interfere. 

The catalytic reduction of oxygen (1.24 mM) was investigated at a BDD electrode under conditions where the electron transfer is mediated by the reduction of anthraquinone monosulfonate (AQ, 50 /rM). The process is thought to be a 2H+, 2e system, where overall the oxygen is reduced to hydrogen peroxide. 

In contrast, the reduction of anthraquinone monosulfonate is found to be nearly reversible on an Au electrode. Its reduction on a BDD electrode is foimd to be slower, as expected, and exhibits a larger peak-to-peak separation. For the case in question, this lowering of the rates of electron transfer is useful as it allows us to directly electrochemicaUy probe the rate of reaction between the reduced anthraquinone and oxygen. 

The reduction of anthraquinone involves the transfer of two electrons although the two transfers are close in potential in aqueous media, the second electron transfer occurs at marginally more negative potential than the first. As a consequence, at low overpotentials significant quantities of the mono-reduced anthraquinone will be formed at the electrode. As the overpotential is further increased the concentration of the monoreduced form decreases as it is reduced futher. On the return scan, as the overpotential is decreased, the concentrations of the monoreduced form will again increase. 

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