Nitro catalyst deactivation

The possibility of using of aliphatic alcohols as hydrogen donors for the catalytic transfer reduction of nitro group over MgO was examined. Catalytic hydrogen transfer was found to be effective and selective method for reduction of nitrobenzene, A-nitrotoluene, A-chloronitrobenzene, 4-nitro-m-xylene, 3-nitro-styrene, 3-nitrobenzaldehyde, 1-nitropropane, and 1-nitrobutane. Conversion of starting nitro compound into desired product depended on the alcohol used as a donor. Adsorption of reactant and catalyst deactivation were studied by esr. New aspects of a role of one-electron donor sites in hydrogen transfer over MgD were demonstrated. 

During catalytic hydrogenation of nitro derivatives, partial reduction of the nitro group yields azo, hydrazo, hydroxylamine, nitroso, or oxime functions, in side products, as a result of catalyst deactivation. Partial reduction may become synthetically useful under carefully chosen conditions, and in substrates where the new formed function cannot interact within the molecule. Nitrobenzene hydrogenation over platinum-on-carbon in a mixture alcohol-dimethyl sulfoxide (as promoter) produces high yields of phenylhydroxylamines ... 

We subsequently developed an efficient catalyst for oxidizing terminal olefins to ketones starting with a non-nitro based catalyst. This catalyst comprised PdCl2, CuCl, LiCl, CH3CN and CuCl2 in tetrahydrofuran or sulfolane solvent. No evidence of catalyst deactivation was observed even after >1(X) turnovers. 

A wide variety of aromatic compounds can be brominated. Highly reactive ones, such as anilines and phenols, may undergo bromination at all activated positions. More selective reagents such as pyridinium bromide perbromide or tetraalkylammonium tribromides can be used in such cases.18 Moderately reactive compounds such as anilides, haloaromatics, and hydrocarbons can be readily brominated and the usual directing effects control the regiochemistry. Use of Lewis acid catalysts permits bromination of rings with deactivating substituents, such as nitro and cyano. 

Esr investigations were done of catalysts samples with reactants adsorbed at room and at reaction temperature. Also the preparations of deactivated and regenerated catalyst were studied. From all studied nitro compounds only the following nitrobenzene (parameters of esr signal g = 2.0031 , a H v = 7 Gs inten-... 

We next tested our nitro-free formulation in tBuOH and found that it also gave high yields of aldehyde, along with the corresponding methyl ketone (Figure 2, Table 1). Catalyst lifetimes seem to be very good as we have never seen definite signs of deactivation. The addition of t-butyl nitrite tended to reduce olefin isomerization but it also reduced the aldehyde yield. 

Oxidation of aromatic amines to nitro-compounds is not normally required. However, in the case of deactivated molecules or in order to obtain specific substitution patterns, this transformation may be useful. The reaction can be carried out by peracids [179], and is readily achieved by the sodium perborate/acetic acid system, in the absence of metal catalysts [180]. Less forcing conditions with peracids can be used to make nitroso-compounds [181]. However, the use of a low excess of oxidant, or of conditions where reaction is slow, encourages coupling of the nitroso-compound with unreacted amine to give a diazo-compound. This can be made deliberately as the major product [182], and will itself undergo further oxidation to the azoxy-compound, which is then hard to oxidise further [183]. 

The Friedel-Crafts alkylation reaction has some limitations. It cannot be applied to an aromatic ring that already has on it a nitro or sulfonic acid group, because these groups form complexes with and deactivate the aluminum chloride catalyst. 

Very recently. Barber et al. reported a tandem reaction combining bifunctional urea and Au(I) salt for the asymmetric synthesis of valuable tetrahydropyridine derivatives [80]. This reaction consisted of a urea-promoted nitro-Mannich reaction of an alkyne-tethered secondary nitroalkane to N-Boc-protected imines and an Au(I) complex-catalyzed intramolecular hydroamination and isomerization (Scheme 9.75). Notably, since the inherent Lewis basic tertiary amine-tethered urea would deactivate the Au catalyst, the reaction system was acidified by additional DPP before addition of an Au catalyst to ensure the success of the overall process. 

---