Anthraquinone reduction

EPR and UV-vis spectroscopy have been combined for example, in the study of anthraquinone reduction [214] and the evolution of species within conducting polymers [145, 215, 216]. The cell used a laminated grid as described above. 

UV-vis methods are often combined with other techniques. For example, combined UV-vis and EPR spectroelectrochemistry was used in the study of anthraquinone reduction. But the EPR spectro-electrochemical cell design is demanding to implement successfully and the presence of the metal electrodes within the cell reduces sensitivity considerably (see later). 

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. 

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 ... 

Although considered an active participant in the process cycle, the tetrahydroaLkylanthraquinone (10) may not be a significant part of the catalytic hydrogenation because, dependent on the concentration in the working solution, these could all be converted to the hydroquinone by the labile shift per equation 17 and not be available to participate. None of the other first- or second-generation anthraquinone derivatives produce hydrogen peroxide, but most are susceptible to further reaction by oxidative or reductive mechanisms. 

WorkingS olution Regeneration and Purification. Economic operation of an anthraquinone autoxidation process mandates fmgal use of the expensive anthraquinones. During each reduction and oxidation cycle some finite amount of anthraquinone and solvent is affected by the physical and chemical exposure. At some point, control of tetrahydroanthraquinones, tetrahydroanthraquinone epoxides, hydroxyanthrones, and acids is required to maintain the active anthraquinone concentration, catalytic activity, and favorable density and viscosity. This control can be by removal or regeneration. 

Only the reduction products involving the keto groups are of any academic or industrial importance. Complete reduction of the keto groups by ammonia and zinc (von Perger method) gives rise to anthracene in good yields and quaUty (10). This method is of importance since substituted anthracenes can be prepared from the corresponding anthraquinones. Industrially, an important dyestuff intermediate, 3-chloroanthracene-2-carboxyhc acid, (2) is prepared by this method (11) from 3-chloroanthraquinone-2-carboxyhc acid [84-32-2]... 

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

Addition of sodium dithionite to formaldehyde yields the sodium salt of hydroxymethanesulfinic acid [79-25-4] H0CH2S02Na, which retains the useful reducing character of the sodium dithionite although somewhat attenuated in reactivity. The most important organic chemistry of sodium dithionite involves its use in reducing dyes, eg, anthraquinone vat dyes, sulfur dyes, and indigo, to their soluble leuco forms (see Dyes, anthraquinone). Dithionite can reduce various chromophores that are not reduced by sulfite. Dithionite can be used for the reduction of aldehydes and ketones to alcohols (348). Quantitative studies have been made of the reduction potential of dithionite as a function of pH and the concentration of other salts (349,350). 

In the benzene and naphthalene series there are few examples of quinone reductions other than that of hydroquinone itself. There are, however, many intermediate reaction sequences in the anthraquinone series that depend on the generation, usually by employing aqueous "hydros" (sodium dithionite) of the so-called leuco compound. The reaction with leuco quinizarin [122308-59-2] is shown because this provides the key route to the important 1,4-diaminoanthtaquinones. 

This derivative is prepared from an A-protected amino acid and the anthrylmethyl alcohol in the presence of DCC/hydroxybenzotriazole. It can also be prepared from 2-(bromomethyl)-9,10-anthraquinone (Cs2C03). It is stable to moderately acidic conditions (e.g., CF3COOH, 20°, 1 h HBr/HOAc, / 2 = 65 h HCl/ CH2CI2, 20°, 1 h). Cleavage is effected by reduction of the quinone to the hy-droquinone i in the latter, electron release from the —OH group of the hydroqui-none results in facile cleavage of the methylene-carboxylate bond. The related 2-phenyl-2-(9,10-dioxo)anthrylmethyl ester has also been prepared, but is cleaved by electrolysis (—0.9 V, DMF, 0.1 M LiC104, 80% yield). ... 

Benzanthrone has been prepared by three general methods, the first of which is generally regarded as the best (i) by heating a reduction product of anthraquinone with sulfuric acid and glycerol,1 or with a derivative of glycerol, or with acrolein. The anthraquinone is usually reduced in sulfuric acid solution, just prior to the reaction, by means of aniline sulfate, iron, , or copper. It has also been prepared (2) by the action of aluminum or ferric chloride on phenyl-a-naphthyl ketone, and (3) from i-phenylnaphthalene-2-carboxylic acid. ... 

Similarly, the hydride reduction of the fluorenone and anthraquinone complexes gives the corresponding secondary alcohols with endo-OH groups resulting from stereospecific attack [134], This strategy is also known in the Cr(CO)3(arene)... 

Bacteria have been isolated using reduced anthraquinone-2,6-disulfonate (HjAQDS) as electron donor and nitrate as electron acceptor (Coates et al. 2002). The organisms belonged to the a-, p-, y-, and 5-subdivision of the Proteobacteria, and were able to couple the oxidation of H AQDS to the reduction of nitrate with acetate as the carbon source. In addition, a number of C2 and C3 substrates could be used including propionate, butyrate, fumarate, lactate, citrate, and pyruvate. 

Redox behavior of anthraquinone is shown in Scheme 4. The quinone moiety may be reduced to the hydroquinone form and converted to a leuco salt under alkali conditions. In general, the leuco salt has a strong affinity for cellulose and is soluble in water. The hydroquinone form is insoluble in water and has low affinity to cellulose. The preferred dyeing procedure depends on the structure and properties of the vat dye. The variables that are used to control the process include, e.g., strength and amount of alkali, reduction temperature, and the presence of salts. During the process of reduction, some side reactions, such as overreduction, hydrolysis,... 

Oxidative repair is not a unique feature of our Rh(III) complexes. We also demonstrated efficient long-range repair using a covalently tethered naphthalene diimide intercalator (li /0 1.9 V vs NHE) [151]. An intercalated ethidium derivative was ineffective at dimer repair, consistent with the fact that the reduction potential of Et is significantly below the potential of the dimer. Thymine dimer repair by a series of anthraquinone derivatives was also evaluated [151]. Despite the fact that the excited triplets are of sufficient potential to oxidize the thymine dimer ( 3 -/0 1.9 V vs NHE), the anthraquinone derivatives were unable to effect repair [152]. We attribute the lack of repair by these anthraquinone derivatives to their particularly short-lived singlet states anthraquinone derivatives that do not rapidly interconvert to the excited triplet state are indeed effective at thymine dimer repair [151]. These observations suggest that interaction of the dimer with the singlet state may be essential for repair. 

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