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Aromatic reductive reactions

In a similar vein, the amino group in sulfide 14 (obtained presumably by an aromatic displacement reaction) is first converted to the bromide by Sandmeyer reaction to give 25. Reduction of the nitro group (16) followed by cyclization gives the substituted phenothiazine. Alkylation with the familiar halide (3) affords dimethothiazine (18). ... [Pg.374]

The name amethyrin refers to the fact that the dull-purple color of the protonated form of the macrocycle is that of amethyst stones, Formal oxidation or reduction products are the aromatic [22]hexaphyrin(l.0.0.1.0.0) or the [26]hexaphyrin(l.0.0,1.0.0), respectively. However, none of these products could be observed either as reaction products or as direct products of oxidation or reduction reactions. [Pg.708]

The numerous biotransformations catalyzed by cytochrome P450 enzymes include aromatic and aliphatic hydroxylations, epoxidations of olefinic and aromatic structures, oxidations and oxidative dealkylations of heteroatoms and as well as some reductive reactions. Cytochromes P450 of higher animals may be classified into two broad categories depending on whether their substrates are primarily endogenous or xenobiotic substances. Thus, CYP enzymes of families 1-3 catalyze... [Pg.921]

White-rot fungus has been used as a biocatalyst for reduction and alkylation. The reaction of aromatic -keto nitriles with the white-rot fungus Curvularia lunata CECT 2130 in the presence of alcohols afforded alkylation-reduction reaction [291]. Alcohols such as ethanol, propanol, butanol, and isobutanol could be used (Figure 8.39d). [Pg.223]

In Part 2 of this book, we shall be directly concerned with organic reactions and their mechanisms. The reactions have been classified into 10 chapters, based primarily on reaction type substitutions, additions to multiple bonds, eliminations, rearrangements, and oxidation-reduction reactions. Five chapters are devoted to substitutions these are classified on the basis of mechanism as well as substrate. Chapters 10 and 13 include nucleophilic substitutions at aliphatic and aromatic substrates, respectively, Chapters 12 and 11 deal with electrophilic substitutions at aliphatic and aromatic substrates, respectively. All free-radical substitutions are discussed in Chapter 14. Additions to multiple bonds are classified not according to mechanism, but according to the type of multiple bond. Additions to carbon-carbon multiple bonds are dealt with in Chapter 15 additions to other multiple bonds in Chapter 16. One chapter is devoted to each of the three remaining reaction types Chapter 17, eliminations Chapter 18, rearrangements Chapter 19, oxidation-reduction reactions. This last chapter covers only those oxidation-reduction reactions that could not be conveniently treated in any of the other categories (except for oxidative eliminations). [Pg.381]

The inertness of ordinary double bonds toward metallie hydrides is quite useful, since it permits reduction of, say, a carbonyl or nitro group, without disturbing a double bond in the same molecule (see Chapter 19 for a discussion of selectivity in reduction reactions). Sodium in liquid ammonia also does not reduce ordinary double bonds, although it does reduce alkynes, allenes, conjugated dienes, and aromatic rings (15-14). [Pg.1008]

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. [Pg.185]

While the cytochrome P-450 monooxygenase reaction described in Eq. (1) often involves hydroxylation of carbon, many other reactions are catalyzed by these enzyme systems. These reactions include oxidation of nitrogen and sulfur, epoxidation, dehalogenation, oxidative deamination and desulfuration, oxidative N-, O-, and S-dealkylation, and peroxidative reactions (56). Under anaerobic conditions, the enzyme system will also catalyze reduction of azo, nitro, N-oxide, and epoxide functional groups, and these reductive reactions have been recently reviewed (56, 57). Furthermore, the NADPH-cytochrome P-450 reductase is capable of catalyzing reduction of quinones, quinonimines, nitro-aromatics, azoaromatics, bipyridyliums, and tetrazoliums (58). [Pg.344]

Zinc in the presence of ammonium chloride reduces primary, secondary and tertiary aliphatic nitro compounds but yields of hydroxylamines are moderate and formation of coupling products is common. Zinc with or without ammonium chloride reduces aromatic nitro compounds (e.g. 75, equation 49) into hydroxylamines in moderate to good yield. However, it has been mentioned that the reaction is sensitive to the grade and quality of zinc dust (equation 50) and aromatic amines have been obtained as major products in zinc reduction reactions. ... [Pg.133]

Aromatic substitution reactions are often complicated and multistep processes. A correlation, however, in many cases can be found between the charged attacking species and the electron density distribution in the molecule attacked during electrophilic and nucleoph c substitution. No such correlation is expected in radical substitution where the attacking particles are neutral, rather a correlation between the reactivities of separate bonds and a free valency index of the bond order. This allows the prediction of the most reactive bonds. Such an approach has been used by researchers who applied quantum calculations to estimate the reactivities of the isomeric thienothiophenes and to compare them with thiophene or naphthalene. " Until recently quantum methods for studying reactivities of aromatics and heteroaromatics were developed mainly in the r-electron approximation (see, for example, Streitwieser and Zahradnik ). The M orbitals of a sulfur atom were shown not to contribute substantially to calculations of dipole moments, polarographic reduction potentials, spin-density distribution, ... [Pg.186]

Oxidative Coupling. A number of cases of this reaction type have been reported. Again, all are really two-step processes involving reduction of metal in the coupling step followed by in situ re-oxidation. Recent examples are coupling of aromatics (II) (Reaction 6),... [Pg.206]

Substitution reactions at aromatic carbon (see also Reduction reactions, Ullmann ether coupling, specific reactions such as Nitration) Arene(tricarbonyl)chromium complexes, 19... [Pg.375]

Systematic investigations of oxidation and reduction reactions of pseudoazulenes are not available. Many pseudoazulenes are sensitive to air but their reaction behavior with other oxidizing reagents is unknown. The air sensitivity of many pseudoazulenes is inconsistent with the aromaticity of these compounds. [Pg.232]

Many of these aromatic reductions proceed with almost quantitative yield, indicating that the reaction... [Pg.40]


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See also in sourсe #XX -- [ Pg.26 ]




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