Catalysis nitroaromatics

More recently, Srivastava and Nicholas discovered the direct allylic amination with nitroaromatics 38 as effective aminating agents under catalysis by the inexpensive [CpFe(CO)2]2 (Scheme 3.38) [134],... 

It is reported that an industrial explosion was initiated by charging potassium hydroxide in place of potassium carbonate to the chloro-nitro compound in the sulfoxide [1], Dry potassium carbonate is a useful base for nucleophilic displacement of chlorine in such systems, reaction being controlled by addition of the nucleophile. The carbonate is not soluble in DMSO and possesses no significant nucleophilic activity itself. Hydroxides have, to create phenoxide salts as the first product. These are better nucleophiles than their progenitor, and also base-destabilised nitro compounds. Result heat and probable loss of control. As it nears its boiling point DMSO also becomes susceptible to exothermic breakdown, initially to methanethiol and formaldehyde. Methanethiolate is an even better nucleophile than a phenoxide and also a fairly proficient reducer of nitro-groups, while formaldehyde condenses with phenols under base catalysis in a reaction which has itself caused many an industrial runaway and explosion. There is thus a choice of routes to disaster. Industrial scale nucleophilic substitution on chloro-nitroaromatics has previously demonstrated considerable hazard in presence of water or hydroxide, even in solvents not themselves prone to exothermic decomposition [2],... 

However, organic pollutants are often accompanied by heavy metal ion contaminants that can be reduced by photogenerated electrons into their less toxic, nonsoluble metallic form. Ti02-assisted photoreductive catalysis was found to be useful in the removal of certain heavy metals including mercury, silver, platinum, palladium, rhodium, and gold via their reduction followed by deposition at the catalyst surface [20-22] or photoreduction of nitroaromatic compounds [23-26]. The use of photogenerated electrons for deposition of metal layers on... 

To reduce the strain associated with cyclization, we next stndied acyclic piperidine precnrsors as nucleophiles to ultimately intercept the Mazzocchi, discovery, and cyanohydrin approaches. Diethyl glutaconate 35 conpled readily with flnoro-4-nitroarenes 30a or 30b to give 36 (95%, HPLC Scheme 3.12)." ° Again, however, ring closnre to 37 did not proceed by either S Ar (36a, X = F) or palladinm catalysis (36b, X = Br). The newly formed ally lie anion of 36 presumably delocalized into the nitroaromatic ring to generate electron-rich character inhibiting subsequent nucleophilic Sf Ar substitution or the oxidative addition required to enter palladinm catalysis pathways. 

The major commercial nitroaromatic hydrogenation by catalysis is the hydrogenation of nitrobenzene to aniline. A Cu catalyst is generally employed since its low activity controls the vigorous exothermic reaction and prevents the formation of cyclohexylamine. The hydrogenation of... 

Aromatic amines have been shown to be intermediates in the metal catalyzed carbonylation of nitroaromatics to aryl carbamates. Previous research established that the novel bis(methoxycarbonyl) complex, Ru(dppe)(C0)2[C(0)0Me]2, was the most abundant species present during catalysis. In this study, the complete kinetic analysis of the reaction of p-toluidine with Ru(dppe)(C0)2[C(0)0Me]2 established that the C-N bond formed by nucleophilic attack on a metal carbonyl, and that the organic product was removed from the metal by an intramolecular elimination of aryl isocyanate. 

Six of the eleven chapters are devoted primarily to the intercalation chemistry of smectite clays, the most versatile among all lamellar compounds. Two of these chapters are devoted to the experimental and theoretical aspects of the clay structures and surface chemistry, including chemical catalysis. Organo clays and polymer-clay nanocomposites, the adsorption of nitroaromatic compounds of environmental significance onto clay surfaces, photochemical processes, and pillared clays and porous clay heterostructures are the subjects of the remaining four chapters. These six chapters provide detailed discussions of the factors that influence access to the intragallery surfaces of the clay host and the materials properties of the resulting intercalates. 

The content of this Handbook reflects the fact that the bulk of knowledge in this field concerns clays. In Part 1, which concentrates on clays, there is considerable focus on clay-organic interactions because of their relevance to catalysis. A chapter on nitroaromatic compound sorption is included because it provides an excellent example of clay-organic interactions. Other pertinent topics include molecular modeling of surface chemistry and photochemical processes, including photocatalysis. Pillared clays and porous clay heterostructures are the subject of an entire chapter. Chapters in Part 2 cover synthesis, characterization, host-guest pillaring, sorption, and catalysis for each class of layered material. 

Anion Source for Palladium Catalysis. The reagent serves as a source of weakly coordinating anions in the palladium-catalyzed formation of mixed phenyl ureas, a known class of commercially available herbicides, using palladium(II) acetate, copper(II) toluenesulfonate, and 2,2 -dipyridyl as the catalyst system. Other studies have suggested that use of this reagent to form palladium salts may have useful applications in the reductive carbonylation of nitroaromatic compounds to give isocyanates via initial carbamate formation (eq 2). ... 

Cyanoaromatics were formed in more than 70% yield under phase transfer catalysis conditions when starting from nitroaromatics in a 2M KCN biphasic water-methylene chloride system in the presence of a catalytic amount of Bn4N CN4 this... 

A notable exception to the rule of thumb that the nitrosoarene compound is favored under oxidative conditions is the observation of arylhydroxylamine rather than nitrosoarene metabolite in microsomal oxidase studies of arylamine metabolism (43). In vitro studies of N-oxidation generally contain the biological reductant NADPH, which can, by a mechanism independent of cytochrome P-450 catalysis, reduce any nitroso product back to the hydroxylamine state. Our studies on CPX-catalyzed oxidation of arylamines by H2O2 did not require a reductant such as NADPH, and thus, may better reflect the actual enzymatic or equilibrium product of oxidative reactions, including microsomal oxidations. Microsomal oxidations in which substrates such as cumene hydroperoxide are used in place of O2/NADPH should yield the nitrosoarene rather than arylhydroxylamine metabolite. In the case of 4-chloroaniline, the nitroso metabolite rather than the hydroxylamine metabolite was produced however, the major product was the nitroaromatic compound, indicative of further oxidation (55). This raises the hypothetical question as to whether... 

Shimizu K, Miyamoto Y, Satsuma A (2010) Size- and support-dependent silver clustta-catalysis for chemoselective hydrogtaiatitm of nitroaromatics. J Catal 270 86-94... 

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