Quinones benzo

The continuous-flow measurements showed the presence of two major compounds. They were afterwards assigned by stop-flow measurements. Peak 1 eluted at 25min, and peak 2 at 41min (see Figure 7.3.2.3). Comparison between the H-NMR spectra recorded during the stop-flow experiments showed that the two compounds are very similar (Figure 7.3.2.5). Peak 1 could be assigned to 2-ethylbenzo-l,4-quinone and peak 2 to 2-ethyl-3-methoxy-benzo-1,4-quinone. 

The vinyl quinones (248) undergo different photochemistry. When these are irradiated a quantitative yield of dimers (249) is obtained. A report has been published dealing with the photocyclisation reactions of benzoyl benzo-1,4-quinones. A laser flash study at 248 nm of vitamin K3 has been reported and... 

A solution of the benzo-1,4-quinone 36 (195 mg, 0.714 mmol), cupric acetate (324 mg. 1.78 mmol) and palladium(n) acetate (15.9 mg, 0.071 mmol) in glacial acetic acid (10 mL) was heated at reflux under air for 19 h. Silica gel (2 g) was added to the reaction mixture, the glacial acetic acid was evaporated in vacuum, and the residue was purified by filtration over silica gel (EtOAc-MeOH, 10 1). After removal of the sol vein, the residue was taken up in chloroform (5 mL), heated at reflux, and subsequently cooled to -30 C. The resulting precipitate wis isolated by filtration, washed with chloroform, and dried in a vacuum lo afford the desired product 2-meihyl-... 

Benzoquinones are highly conjugated molecules and are consequently coloured. Benzo-1,4-quinone itself is yellow and benzo-1,2-quinones are often red. Chloranil forms glistening yellow platelets on crystallization from fuming nitric acid Quinones occur naturally and some natural pigments contain a quinone unit... 

Trihydroxybiphenyls have been synthesised by coupling benzo-1,4-quinones with phenolates. Thus the dichloroaluminium salt of 4-tert-butylphenol (formed by reaction of the phenol in carbon disulphide with aluminium chloride) upon addition to the 2-methyl-benzo-1,4-quinone/ aluminium chloride (1 2)... 

Oxidation, (a) Ammoniacal silver nitrate. To a few ml. of ammoniacal AgNOj (preparation, p. 525), add a few drops of cold aqueous benzo quinone solution a silver mirror or (more generally) a dark precipitate of metallic silver is formed in the cold. 

In addition to CuCfi, some other compounds such as Cu(OAc)2, Cu(N03)2-FeCl.i, dichromate, HNO3, potassium peroxodisulfate, and Mn02 are used as oxidants of Pd(0). Also heteropoly acid salts comtaining P, Mo, V, Si, and Ge are used with PdS04 as the redox system[2]. Organic oxidants such as benzo-quinone (BQ), hydrogen peroxide and some organic peroxides are used for oxidation. Alkyl nitrites are unique oxidants which are used in some industrial... 

Some other inhibitors from the patent literature include hydroquinone [129], ionoP [130], and quinone [131]. Other inhibitors used to stabilize MMA include butylated hydroxy toluene (BHT), phenothiazine, methylene blue, hydroxy-diphenylamine and di-/jc/<3-napthol [132]. Several good reviews of inhibition and inhibitors have been written [133-136]. The mechanisms of inhibition are subtle and complicated. For example, it has been reported that highly purified benzo-quinone acts as a retarder rather than an inhibitor [137]. It has been proposed... 

Oxidations of pyridopyrimidines are rare, but the covalent hydrates of the parent compounds undergo oxidation with hydrogen peroxide to yield the corresponding pyridopyrimidin-4(3 T)-ones. Dehydrogenation of dihydropyrido[2,3-(i]pyrimidines by means of palladized charcoal, rhodium on alumina, or 2,3-diehloro-5,6-dicyano-p-benzo-quinone (DDQ) to yield the aromatic derivatives have been reported. Thus, 7-amino-5,6-dihydro-1,3-diethylpyrido[2,3-d]-pyri-midine-2,4(lif,3f/)-dione (177) is aromatized (178) when treated with palladized charcoal in refluxing toluene for 24 hours. 

Ethoxy-3//-azepin-3-ones, e.g. 2, are produced rapidly (2-20 min), as yellow gums, by the oxidation of 7-ethoxy-6-hydroxy-4/T-azepines,e.g. 1, with2,3-dichloro-5,6-dicyano-l,4-benzo-quinone (DDQ) in benzene.48,51... 

In its catalyzed form [catalyzed with hydroquinone (HQ), benzo-quinone, or copper], DEHA has a very fast reaction rate, almost as fast as catalyzed sulfite. Hydroquinone is the most popular catalyst for DEHA, and it is likely that the rapid reaction rate is, in part at least, due to the catalyst simply acting as an oxygen scavenger in its own right. 

B. 2-Chloro-3,6-di-tert-butyl-l,4-benzoquirwne. A 2-1. Erlenmeyer flask is charged with a solution of 112 g. (0.385 mole) of 2,3-dichloro-2,5-di-fer<-butylcyclohex-5-ene-l,4-dione in 800 ml. of ether. A solution of 28.4 g. (0.383 mole) of diethylamine (N-ethylethanamine) in 50 ml. of ether is added in one portion to the vigorously swirled flask (Note 5). The reaction is instantaneous, resulting in a voluminous precipitate. The mixture is washed with two 1-1. portions of water and then with 500 ml. of aqueous saturated sodium chloride. The yellow ether solution is dried over anhydrous magnesium sulfate, the drying agent removed by filtration, and the solvent removed on a rotary evaporator to yield 96-97 g. (98-99%) of 2-chloro-3,6-di-ferf-butyl-l,4-benzo-quinone as a yellow oil which is used without further purification (Note 6). 

Cyclic conjugation is continuous in o-benzoquinone and discontinuous in p-benzoquinone (Scheme 15, cf. Scheme 4). The donors (the C=C bonds) are on one side of the cyclic chain and the acceptors (the C=0 bonds) are on the other side in o-benzoquinone. In p-benzoquinone the donors and the acceptors are alternatively disposed along the chain. The thermodynamic stability of o-benzo-quinone is under control of the orbital phase property. The continuity conditions are not satisfied. o-Benzoquinone is antiaromatic. The thermodynamic stability of p-benzoquinone is free of the orbital phase (neither aromatic nor antiaromatic) and comes from the delocalization between the four pairs of the neighboring donors and acceptors. In fact, p-benzoquinone, which melts at 116 °C, is more stable than o-benzoquinone, which decomposes at 60-70 °C. 

The composition of the electrical effect in the case of the 1,4-benzo-quinones seems to depend upon the degree of substitution. The association constants and charge transfer absorption energies of the 2-substituted-l,4-benzo-quinone-hexamethylbenzene complexes (sets 15-2 and 154) show values of pj of 55 and 44 respectively. Values of p are set forth in Table XVII. 

Fig. 21.—A comparison of the effects of 0.1 percent of benzo-quinone (curve II), 0.5 percent of nitrobenzene (curve III), and 0.2 percent of nitrosobenzene (curve IV) on the thermal polymerization of styrene at 100°C. Curve I represents the polymerization of pure styrene. (Results of Schulz. )...

Commercially available 2,3-dichloro-5,6-dicyano-l,4-benzo-quinone was employed. 1,6-Methano[10]annulene was obtained in equally good yields, when 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, prepared by the method of Walker and Waugh,4 was utilized. 

Since a2 + b2 > 2ab for all positive values of a and b, except a = b 0, we conclude that S, 3 (ortho) > S 3 (para). Consequently, the pi LUMO of ortho benzo-quinone will be lower in energy than the pi LUMO of para benzoquinone. Furthermore, the degeneracy of the oxygen lone pair AO is lifted more in the case of ortho benzoquinone. The final conclusion is that the mr transition is predicted to occur at longer wavelengths in the ortho isomer relative to the para isomer. 

The palladium(II)-mediated oxidative cyclization is also applied to the synthesis of carbazole-l,4-quinone alkaloids. The required arylamino-l,4-benzo-quinones are readily prepared by arylamine addition to the 1,4-benzoquinone and in situ reoxidation of the resulting hydroquinone [131]. 

Addition of the arylamines 117 to 2-methoxy-3-methyl-l,4-benzoquinone 118 affords regioselectively the 5-arylamino-2-methoxy-3-methyl-l,4-benzo-quinones 119 (Scheme 37). Palladium(II)-catalyzed oxidative cyclization leads to the carbazole-l,4-quinones 28 [135,136],previously obtained by the iron-mediated approach (cf. Scheme 14). Regioselective addition of methyllithium to the quinones 28 provides carbazomycin G 29a and carbazomycin H 29b [96,135]. Reduction of 29a with lithium aluminum hydride followed by elimination of water on workup generates carbazomycin B 23a [135]. Addition of heptylmag-... 

Ether cleavage of 4-heptyl-3-methylveratrole 121 using boron tribromide affords 4-heptyl-3-methylcatechol 122 (Scheme 38). Oxidation of the catechol 122 with o-chloranil to 4-heptyl-3-methyl-l,2-benzoquinone 123 and subsequent immediate addition of aniline leads to 5-anilino-4-heptyl-3-methyl-l,2-benzo-quinone 124. Unlike the very labile disubstituted ort/zo-quinone 123, compound 124 is stable and can be isolated. Palladium(II)-mediated oxidative cyclization of the anilino-l,2-benzoquinone 124 provides carbazoquinocin C 51. 

Popp BV, Stahl SS (2007) Palladium-Catalyzed Oxidation Reactions Comparison of Benzo-quinone and Molecular Oxygen as Stoichiometric Oxidants. 22 149-189 Prashad M (2004) Palladium-Catalyzed Heck Arylations in the Synthesis of Active Pharmaceutical Ingredients. 6 181-204 Prestipino C, see Zecchina A (2005) 16 1-35 Pretraszuk C, see Marciniec B (2004) 11 197-248... 

Dichloro-2-hydroxy-5-2, 4, 5, 6 -tetrachloro-3-hydroxyphenoxy-p-benzo-quinone, see... 

These carbonylation reactions can also take place by using catalytic amounts of Pd(II) salts in the presence of an oxidant such as CUCI2, CUCI/O2, FeClj, Ce(lV) salts or benzo-quinone, the most effective of them being CuCl2. °... 

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