Anthraquinone from benzoquinone

The 13C NMR spectral data for 9, 16, and 17 are shown in Table 2. The chemical shifts of carbonyl carbons of anthraquinones are characteristically observed at about 180 ppm.9 The chemical shifts for carbonyl carbons of 1,4-naphthoquinone and 1,4-benzoquinone appear at about 185 ppm, while those of carbonyl carbons adjacent to a methylene or methyl carbon are at about 200 ppm. The chemical shifts of the Cl and C4 of 9 are observed at 200.8 ppm and assigned to the 1,4-diketo form 9a. In the 13C spectrum of 17, the chemical shifts of carbonyl carbons are at 199.9 and 172.2 ppm. The former value corresponds to a carbonyl carbon adjacent to the methylene carbon, and the latter corresponds to the carbonyl carbon in the 9-position. The methylene carbons of 17 show two signals at 34.5 and 23.8ppm. From these results, 17 is considered to exist exclusively as an unsymmetrical 4,9-diketo form, 17a. Thus, these NMR spectral data suggest... 

The zinc porphyrin P-2 with an appended hydroquinone can form complexes with quinones via H-bonds and charge-transfer interactions. In such complexes, PET from the porphyrin to the quinone is possible, and efficient fluorescence quenching was indeed observed upon binding with substituted benzoquinones, naphthaquinones and anthraquinones. 

The phytochemical reducibility of quinones was first demonstrated in the case of p-xyloquinone. This compound is worthy of interest since it is very easily formed from diacetyl by purely chemical means through a type of aldol condensation followed by ring closure. It is reduced to p-xylohydroquinone by fermenting yeast. Benzoquinone, thymoquinone and a-naphthoquinone similarly yield the corresponding hydroquinones. Tetrabromo-o-quinone and anthraquinone proved resistant to attack, while phenanthraquinone could be reduced phyto-chemically to phenanthrahydroquinone in poor yield (9%). Phytochemical reduction can also be accomplished in the dicyclic terpene series. According to unpublished experiments by Neuberg and Peiser, 2,3-dihy-... 

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. 

Excellent yields of adduct have been obtained from a variety of o-quinones, including o-benzoquinone, 1,2-naphthaquinone, phen-anthraquinone, 5,6-chrysenequinone, and many of their simple derivatives, including the heterocyclic quinone 326 benzo[A]quinoline-5,6-quinone. Lower yields are in general observed for aromatic diketones such as benzil,327 and the reaction does not appear to occur to any appreciable extent with aliphatic a-diketones. 

The simplest quinones are o- and p-benzoquinone [(3) and (4) respectively]. This quinonoid structural feature is widespread in naturally occurring compounds isolated from moulds, fungi, lichens, plants and insects,52 which include not only substituted benzoquinones but also substituted polycyclic quinones [i.e. the substituted analogues of, for example, 1,2-naphthoquinone (5), 9,10-anthraquinone (6), and 9,10-phenanthraquinone (7)]. 

Eleven 9,10-anthraquinones with various substituents, seven 1,4-naphthoquinones, 1,2-naphthaquinone and five 1,4-benzoquinones were used as QA. These quinones provide a series of RCs with a variation of the reaction exothermicity, - AG , from 0.11 to 0.9 eV. The rates of intraprotein electron transfer from various Qa to (BChl)J were found to be virtually temperature independent from 5 to 100 K and to decrease severalfold from 100 to 300 K. Only a small change of the rate upon the — AG° variation was found when reaction was made more exothermic than in the native RC. As the reaction was made less exothermic, the rate decreased notably without becoming temperature dependent. 

Fig. 12a—e. H CIDNP spectra of diethylvinylamine observed during the reaction of (a) anthraquinone with triethylamine, (b) benzoquinone with triethylamine in acetone-d6, (c) benzoquinone with triethylamine in acetonitrile-d3. Traces (d) and (e) show theoretical spectra calculated for the exclusive involvement of the aminoalkyl radical and of the aminium radical ion, respectively. The change from emission (trace a) to enhanced absorption (trace c) for the doublets near 6.0 ppm indicates an increasing involvement of the aminium radical ion [178]... 

Clostridium thermoaceticum contains the so-called AMAPOR (artificial-media-tor-accepting pyridine-nucleotide oxidoreductases), which are useful for electro-microbial regeneration of all four forms of pyridine nucleotides, too. An NADP(H) dependent AMAPOR from C. thermoaceticum has been purified and characterized [104]. It is able to react with rather different artificial mediators such as viologens or quinones, for example 1,4-benzoquinone, anthraquinone-2,6-disulfonate, or 2,6-dichloro-indophenol. 

Me R = Br, R = H) by various donors in viscous soJventa are decreased by a factor of <2 in a 0.34 T magnetic field and pressure is reported to accelerate the photoreduction of p-benzoquinone in SOS and CTAB micelles in Aerosol OT reversed micelles, the reaction is retarded.The yield of anthraquinone-2-sulphonate radical anion (AQS) generated by irradiation of AQS in aqueous acetonitrile containing propan-2-oJ has been found to depend on the water concentration and to follow Perrin s equation.Complexation of aryl alkyl ketones with /3-cyclodextrin leads to changes in the ratio of the products of elimination and cyclisation which result from reaction of the... 

Unfortunately anthrahydroquinone is not very stable under acid conditions, which are needed for a reversible cyclization of the benzoquinone derivatives. There is an early preparative observation on the rapid formation of anthraquinone (AQ) 3 and anthrone (Ant) 4 from anthrahydroquinone (AQH2) 1 in cold concentrated sulfuric acid [83] according the overall reaction... 

Thus such a mild electron-acceptor molecules as p-benzoquinone (electron affinity 0.9 ev) and anthraquinone can, like the strong electron acceptor chloranil (electron affinity = 1.35 ev), abstract an electron from the ZnO, a semiconductor of the n-type. The abstracted electrons come from the local levels below and close to the conduction band, so that at room temperature they can migrate to the electron traps formed on the surface by the adsorbed electron acceptor. The accepting of an electron by the neutral quinone molecule, immediately leads to a redistribution of the valency bonds into the configuration of the anion radical (c). 

The genera Trichoderma and Gliocladium, anamorphs of Hypocrea, have been perhaps the most studied of the fungal organisms which show potential as BCAs. From early investigations of the metabolites produced, a number of simple resorcinols, /7-benzoquinones and anthraquinones were characterised and shown to have antifungal activity. This work will not be considered here since it has been comprehensively reviewed previously [72]. 

Folk medicine has attributed antitumor properties to preparations from medicinal plants containing quinones. Quinones for the anthraquinone, naphtoquinone and benzoquinone group were studied for their inhibitory growth effect on cultured malignant cells, which include cultured ovarian, breast, prostate, melanoma, lung, colon and pancreatic cancer cells... 

Ultraviolet and visible light (UV-VIS) analysis is the most used identification technique for anthraquinones. The UV-VIS absorption spectrum of an anthraquinone is a combination of the absorptions arising from partial acetophenone- and benzoquinone chromophores (Fig. (7)) [1,20,62]. 

However, the fluorescence of the P-CD sandwiched porphyrin 81 (schematic representation reprinted with permission from reference 240) was not quenched by 1,4-benzoquinone [240]. Efficient quenching and biexponential decay of the emission were observed in presence of 1,4-naphthoquinone, of 9,10-anthraquinone-2-sulfonate and of a benzoquinone functionalized with adamantane. The fluorescence quenching was always accompanied by variations of the absorption Q band of the porphyrin, which indicated ground-state association between 81 and the quinones. These data indicate that association between 81 and the quinones is a prerequisite for electron transfer. 

FIG. 4 Logarithmic plots of the bimolecular rate constants for ( ) the oxidation ( cat,ox/ M,ox) and (B) the reduction (fccat,red/AM,red) of DI with mediators as a function of the formal potential of the mediators (Fm ) pH 8.5. MV methyl viologen ARS alizarin red S FMN flavin mononucleotide FAD flavin adenine dinucleotide 2,6AQS anthraquinone-2,6-sulfonate VK3, 2-methyl-1,4-naphthoquinone NQ 1,4-naphthoquinone, 2,6DMBQ 2,6-dimethylbenzoquinone BQ 1,4-benzoquinone AP p-aminophenol FMA ferrocenylmethanol. (From Ref. 16.)... 

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