Quinones p-benzoquinone

Benzoquinone, see p-Quinone p-Benzoquinone, see p-Quinone Benzoyl alcohol, see Benzyl alcohol... 

Polar effects appear to be of prime importance in determining the effect of quinones. p-Benzoquinone and chloranil (which are electron-poor) act as inhibitors toward electron-rich propagating radicals (vinyl acetate and styrene) but only as retarders toward the electron-poor acrylonitrile and methyl methacrylate propagating radicals. A further observation is that the inhibiting ability of a quinone toward electron-poor monomers can be increased by the addition of an electron-rich third component such as an amine. Thus the presence of triethylamine converts chloranil from a very weak retarder to an inhibitor toward methyl methacrylate. 

The course of a typical hydrogenation of quinone (p-benzoquinone), catalyzed by cuprous acetate in quinoline solution, is shown in Fig. 1. As indicated here, the quantity of hydrogen absorbed increases linearly with time until a point is reached where a change in slope occurs. The... 

Except under extreme conditions, oxidation of the benzene ring requires the presence of strongly electron-donating groups such as hydroxyl or amino. These groups are simultaneously oxidized. The best known products of this oxidation process are the quinones benzo-l,4-quinone (p-benzoquinone, cyclohexadiene-l,4-dione, 10) and benzo-l,2-quinone (o-benzoquinone, cyclohexadiene-l,2-dione, 11). 

Benzoy lace tone Quinones, p-Benzoquinone, Anthraquinone Diphenoquinones Ketenes, CH2— CO, (CsH,)2C CO Monosaccharides T>-Lactose hydrate HCOCOOH Pyruvic acid, Levulinic acid Acetals (NHJ2COS... 

Formaldehyde, Benz-aldehyde, p-Dimethyl-amino-, m-Nitro-benzaldehyde Acetone, Benzophenone Acetylacetone, Benzoylacetone Quinones, p-Benzoquinone Dichlorodicyanoquinone Ketene... 

Benzophenone, fi-Acetonaphthone Acetylacetone, Benzoylacetone Quinones, p-Benzoquinone Diphenoquinones Ketenes, (CgH )2C=CO Monosaccharides D-Lactose hydrate HCOCOOH... 

Quinones are colored p-benzoquinone, for exanple, is yellow. Many occur naturally and have been used as dyes. Alizarin is a red pigment extracted from the roots of the madder plant. Its preparation from anthracene, a coal tar derivative, in 1868 was a significant step in the development of the synthetic dyestuff industry. 

Arylation of enamines with p-benzoquinones takes a somewhat different course (70). The enamine (16) reacts exothermally with p-benzoquinone in benzene solution to give 2-(dimethylamino)-2,3-dihydro-3,3-dimethyl-5-benzofuranol (92). The reaction of enamines with quinone dibenzenesul-fonimide proceeds similarly (68). The product from the enamine (28) is the tetrahydrocarbazole derivative (93). 

Reactions of quinones with enamino ketones have not been reported, but ethyl (S-anilinocrotonate (94), an enamino ester, has been shown to condense (71) with p-benzoquinone to give l-phenyl-2-methyl-3-carbethoxy-5-hydroxyindole (95). 

The absolute rate constants for attack of carbon-centered radicals on p-benzoquinone (38) and other quinones have been determined to be in the range I0M08 M 1 s 1.1 -04 This rate shows a strong dependence on the electrophilicity of the attacking radical and there is some correlation between the efficiency of various quinones as inhibitors of polymerization and the redox potential of the quinone. The complexity of the mechanism means that the stoichiometry of inhibition by these compounds is often not straightforward. Measurements of moles of inhibitor consumed for each chain terminated for common inhibitors of this class give values in the range 0.05-2.0.176... 

Benzenediol, quinol, or p-dihydroxy benzene [CgH4-l,4-(OH)2] has a MW of 110.1. It is a white crystalline powder formed by the reduction of p-benzoquinone [quinone, CgH4 ( 0)2],... 

Scheme 2.7). The phenols were formed during isolation (chromatography on silica gel) from the corresponding cycloadducts. In the reaction with p-benzoquinone, a product was unexpectedly obtained from a hetero-T>ie s-Alder reaction with the quinone acting as a carbonyl dienophile. 

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. 

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