Production of quinones

The close electrochemical relationship of the simple quinones, (2) and (3), with hydroquinone (1,4-benzenediol) (4) and catechol (1,2-benzenediol) (5), respectively, has proven useful in ways extending beyond their offering an attractive synthetic route. Photographic developers and dye syntheses often involve (4) or its derivatives (10). Biochemists have found much interest in the interaction of mercaptans and amino acids with various compounds related to (3). The reversible redox couple formed in many such examples and the frequendy observed quinonoid chemistry make it difficult to avoid a discussion of the aromatic reduction products of quinones (see Hydroquinone, resorcinol, and catechol). 

Polyakov, N. E., V. V. Konovalov et al. (2001a). One-electron transfer product of quinone addition to carotenoids EPR and optical absorption studies. J. Photochem. Photobiol. A 141 117-126. 

At longer reaction times, the formation of an acidic product, probably cfs,cfs-muconic acid, and a copper containing precipitate were observed. This latter could be a polynuclear product of quinone and semiquinone fragments (37,38). In agreement with this stoichiometry, about 50% of 02 was regenerated by adding a small amount of catalase to the reaction mixture at relatively short reaction times. 

Phenolic oxidation by PPO and POD in B-deficient leaves leads to the production of quinones. These compounds are known for their high toxicity, and for being responsible for the production of oxygenated radicals such as H2O2 and O2. The accumulation of quinones in plants that act as indicators of the deficiency has been considered as the prime cause of cell damage and of growth reduction [127]. 

Diepoxides from Diels-Alder addition products of quinone with two molecules of butadiene, which exist as several isomers (f.p., 179°, 186°, 216°, 260°, and 320°C. 

Some conclusions as to the constitution of aniline black are obtained from its decomposition on oxidation and reduction. The production of quinone in the former, and of paraphenylamine, c., in the latter, render it apparent that the nitrogen atom of one benzene residue enters the chain of another benzene residue in the para position to the nitrogen atom, Goppelsroeder s formula [15], in which the benzene chains are represented as linked in a circle of imido-groups, corresponds to this view to a certain extent. This entirely symmetrical formula, however, does not account for the tinctorial character of the compound in a satisfactory manner and from the formation of a stable leuco-compound it may be deduced that in all probability at least two nitrogen atoms of the molecule are linked together. 

The polymer boxmd peroxocomplexes prepared in the present work have excellent catalytic potentiality and selectivity in the production of quinones. The chromium peroxocomplexes loses its activity on reaction and could be regenerated. The pwlymer bound vanadium catalyses sharpless epoxidation reactions. The high pore volume and a marginally good surface area shows that GMA-EGDM copolymers are good choice as supports. 

Vitamin E is the most important lipid-soluble antioxidant in biological systems. (all-rac)-a-Tocopherol (synthetic vitamin E, 1) is the economically most important product industrially prepared on a multi-10 OOOt/year scale and mainly used in animal nutrition [50]. In the large-scale syntheses of 1, 2,3>5-trimethylhydroquinone (6) is used as the aromatic key building block, which is condensed with isophytol (2) to yield 1 by all producers worldwide (Scheme 7.1). Trimethylhydroquinone (TMHQ, 6), in turn, is obtained from trimethylquinone (TMQ, 5) by reduction procedures, in particular catalytic hydrogenation. Besides other possibilities to access TMHQ (6), this route is generally preferred, and efficient oxidation processes for the production of quinone 5 from alkylated phenols are, therefore, of high interest [51]. 

Phenols and enolizable ketones that cannot undergo Q , -dehy-drogenation may afford intermolecular products arising from either C-C or C-0 coupling on treatment with DDQ in methanol. 2,6-Dimethoxyphenol, for example, results predominantly in oxidative dimerization (eq 21), while the hindered 2,4,6-tri-r-butyl-phenol generates the product of quinone coupling (eq 22). Various other unusual products have been observed on DDQ oxidation of phenols and enolic compounds, their structure being dependent on that of the parent compound. ... 

Pereira Netto et al. (2000) cite another two mechanisms to explain PAHs activation. The first would be related with the formation of benzilic esters, electrophilic, by a series of substitution reactions. The second would be the de-hydrogenation of dihydrodiols metabolites, which lead to the production of quinones, substances that are capable of reacting, directly, with DNA or with O2, generating reactive oxygen species such as hidroxil radicals or superoxide anions, which attack DNA. 

The theory of sublimation, t.e. the direct conversion from the vapour to the sohd state without the intermediate formation of the liquid state, has been discussed in Section 1,19. The number of compounds which can be purified by sublimation under normal pressure is comparatively small (these include naphthalene, anthracene, benzoic acid, hexachloroethane, camphor, and the quinones). The process does, in general, yield products of high purity, but considerable loss of product may occur. 

Benzoquinone ( quinone ) is obtained as the end product of the oxidation of aniline by acid dichromate solution. Industrially, the crude product is reduced with sulphur dioxide to hydroquinone, and the latter is oxidised either with dichromate mixture or in very dilute sulphuric acid solution with sodium chlorate in the presence of a little vanadium pentoxide as catalyst. For the preparation in the laboratory, it is best to oxidise the inexpensive hydroquinone with chromic acid or with sodium chlorate in the presence of vanadium pent-oxide. Naphthalene may be converted into 1 4-naphthoquinone by oxidation with chromic acid. 

Quaternary structure (Section 27 22) Description of the way in which two or more protein chains not connected by chemical bonds are organized in a larger protein Quinone (Section 24 14) The product of oxidation of an ortho or para dihydroxybenzene denvative Examples of quinones include... 

Uses. About 35% of the isophthahc acid is used to prepare unsaturated polyester resins. These are condensation products of isophthahc acid, an unsaturated dibasic acid, most likely maleic anhydride, and a glycol such as propylene glycol. The polymer is dissolved in an inhibited vinyl monomer, usually styrene with a quinone inhibitor. When this viscous hquid is treated with a catalyst, heat or free-radical initiation causes cross-linking and sohdification. A range of properties is possible depending on the reactants used and their ratios (97). 

Methylenebis(2,6-di-/ /f-butylphenol) (25) (R = H) [118-82-17, the reaction product of two molecules of 2,6-DTBP with formaldehyde under basic conditions, is a bisphenoHc antioxidant. The quinone methide in this case is generated in situ. The product results from the addition of 2,6-di-/ /f-butylphenolate to (23) (12). 

The most extensive mechanistic studies of quinone Michael addition chemistry involve the arylsufinic acids, which yield reduced product (50,51). The sulfones produced in such reactions have been examined electrochemicaHy (48) and kineticaHy (52). The influence of substitutents in the quinone has... 

In the case of l,4-ben2oquinone, the product is steam-distilled, chilled, and obtained in high yield and purity. Direct oxidation of the appropriate unoxygenated hydrocarbon has been described for a large number of ring systems, but is generally utilized only for the polynuclear quinones without side chains. A representative sample of quinone uses is given in Table 5. 

The recommended daily allowance for vitamin E ranges from 10 international units (1 lU = 1 mg all-rac-prevent vitamin E deficiency in humans. High levels enhance immune responses in both animals and humans. Requirements for animals vary from 3 USP units /kg diet for hamsters to 70 lU /kg diet for cats (13). The complete metaboHsm of vitamin E in animals or humans is not known. The primary excreted breakdown products of a-tocopherol in the body are gluconurides of tocopheronic acid (27) (Eig. 6). These are derived from the primary metaboUte a-tocopheryl quinone (9) (see Eig. 2) (44,45). 

Benzoquinone [106-31-4J, (quinone) has been reported as a by-product of benzene oxidation at 410—430°C. Benzene can be oxidized to phenols... 

Ethyl Acetate. The esterification of ethanol by acetic acid was studied in detail over a century ago (357), and considerable Hterature exists on deterrninations of the equiUbrium constant for the reaction. The usual catalyst for the production of ethyl acetate [141-78-6] is sulfuric acid, but other catalysts have been used, including cation-exchange resins (358), a- uoronitrites (359), titanium chelates (360), and quinones and their pardy reduced products. 

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

One-electron reduction of a-dicarbonyl compounds gives radical anions known as setnidiones. Closely related are the products of one-electron reduction of aromatic quinones, the semiquinones. Both semidiones and semiquinones can be protonated to give neutral radicals which are relatively stable. 

Other investigations of interest are the studies of the isomeric dihydroderivatives of brucine and strychnine and their reactions, carried out by Leuchs and his collaborators, investigation of the red o-quinone (isolated as the perchlorate, CjiHjoO Ng. HCIO4) formed in the well-known test for brucine with nitric acid, and the examination of the transformation products of oximinobrucine by Wieland et al. ... 

Quinone (Section 24.14) The product of oxidation of an ortho or para dihydroxybenzene derivative. Examples of quinones include... 

The main product of the Elbs reaction is the 1,4-dihydroxybenzene (hydro-quinone). If the para position is already occupied by a substituent, the reaction occurs at an ortho position, leading to a catechol derivative although the yields are not as good as for a hydroquinone. Better yields of catechols 7 can be obtained by a copper-catalyzed oxidation of phenols with molecular oxygen ... 

Fenoldopam (76) is an antihypertensive renal vasodilator apparently operating through the dopamine system. It is conceptually similar to trepipam. Fenoldopam is superior to dopamine itself because of its oral activity and selectivity for dopamine D-1 receptors (D-2 receptors are as.sociated with emesis). It is synthesized by reduction of 3,4-dimethoxyphenylacetonitrile (70) to dimethoxyphenethylamine (71). Attack of diis last on 4-methoxystyrene oxide (72) leads to the product of attack on the epoxide on the less hindered side (73). Ring closure with strong acid leads to substituted benzazepine 74. O-Dealkylation is accomplished with boron tribromide and the catechol moiety is oxidized to the ortho-quinone 75. Treatment with 9NHC1 results in conjugate (1,6) chloride addition and the formation of fenoldopam (76) [20,21]. 

Transformation products of stabilizers formed during melt processing may exert either or both anti- and/ or pro-oxidant effects. For example, in the case of BHT, peroxydienones, PxD (reactions 9b, b") lead to pro-oxidant effects, due to the presence of the labile peroxide bonds, whereas quinonoid oxidation products, BQ, SQ, and G- (reaction 9 b, c, d) are antioxidants and are more effective than BHT as melt stabilizers for PP [29], The quinones are effective CB—A antioxidants and those which are stable in their oxidized and reduced forms (e.g., galvinoxyl, G-, and its reduced form, hydrogalvi-noxyl, HG) may deactivate both alkyl (CB—A mecha-... 

The redox properties of quinones are crucial to the functioning of living cells, where compounds called ubiquinones act as biochemical oxidizing agents to mediate the electron-transfer processes involved in energy production. Ubiquinones, also called coenzymes Q, are components of the cells of all aerobic organisms, from the simplest bacterium to humans. They are so named because of their ubiquitous occurrence in nature. 

It was previously mentioned in Section 1.2 that the products of diazotizing o- and /7-aminophenols exist in neutral aqueous solutions as zwitterions (1.7 b) which are mesomeric with the corresponding quinone diazides (1.7 a). They can therefore be... 

For many decades intramolecular O-coupling was considered not to take place in the diazotization products of 2-aminophenol and its derivatives (for a contrary opinion see, however, Kazitsyna and Klyueva, 1972). The compounds were assumed to be present as one structure only, which can be represented as a mesomer of a phenoxide diazonium zwitterion 6.63 b and a diazocyclohexadienone 6.63 a (see reviews by Kazitsyna et al., 1966 Meier and Zeller, 1977 Ershov et al., 1981). In IUPAC nomenclature 6.63 is called 1,2-quinone diazide, in Chemical Abstracts 6-diazo-2,4-cyclohexadien-one (see Sec. 1.3). More recently, however, Schulz and Schweig (1979, 1984) were able to identify the intramolecular product of O-coupling, i.e., 1,2,3-benzooxadiazole (6.64) after condensation of 6.63 in vacuo at 15 K in the presence of argon (see Sec. 4.2). 

The photolysis of o-quinone diazides was carefully investigated by Stis in 1944, many years before the development of photoresists. Scheme 10-102 shows the photolysis sequence for the diazoquinone 10.75 formed in the diazotization of 2-amino-1-naphthol. The product of the photolytic step is a ketocarbene (10.76), which undergoes a Wolff rearrangement to a ketene (10.77). In the presence of water in-dene-3-carboxylic acid (10.78) is formed this compound is highly soluble in water and can be removed in the development step. The mechanism given in Scheme 10-102 was not postulated as such by Stis, because in 1944 ketocarbenes were unknown (for a mechanistic discussion of such Wolff rearrangements see review by Zollinger, 1995, Sec. 8.6, and Andraos et al., 1994). 

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