Reduction to amines

Aromatic nitro compounds include both important explosives and a number of agrochemicals. Concern with their fate has motivated extensive examination of their reduction to amines under a range of conditions. 

Nitrotoluenes including 2,4,6-trinitrotoluene (TNT) are important components of explosives and several nitroarenes including the antibacterial nitrofurans have established mntagenicity (Purohit and Basu 2000). Substantial effort has been directed to the degradation of nitroarenes, and to their reduction to amines. Although nitroarene reductases, noted in Chapter 3, Part 3, are distribnted in a range of biota, the products may not necessarily represent intermediates in the degradation... 

Aromatic azo compounds, many of which are sulfonated, are components of many commercially important dyes, colorants, and pigments, so that attention has been directed to their degradation and transformation. These compounds are often considered recalcitrant, although then-transformation has been accomplished by reduction to amines with scission of the Ar-N=N-Ar bond to produce arylamines. The amines may then be degraded, for example, 6-aminonaphthalene-2-sulfonate by dioxygenation and ring fission to 5-aminosalicylate (Hang et al. 1991). This is then... 

Only limited data are available on full- or pilot-scale operations, and the results from these may present an oversimplified view. In general reduction to amines is the initial—and sometimes the only—transformation. 

In recent years, the importance of aliphatic nitro compounds has greatly increased, due to the discovery of new selective transformations. These topics are discussed in the following chapters Stereoselective Henry reaction (chapter 3.3), Asymmetric Micheal additions (chapter 4.4), use of nitroalkenes as heterodienes in tandem [4+2]/[3+2] cycloadditions (chapter 8) and radical denitration (chapter 7.2). These reactions discovered in recent years constitute important tools in organic synthesis. They are discussed in more detail than the conventional reactions such as the Nef reaction, reduction to amines, synthesis of nitro sugars, alkylation and acylation (chapter 5). Concerning aromatic nitro chemistry, the preparation of substituted aromatic compounds via the SNAr reaction and nucleophilic aromatic substitution of hydrogen (VNS) are discussed (chapter 9). Preparation of heterocycles such as indoles, are covered (chapter 10). 

Nitro-PAH were determined by capillary GC-MC, after reduction to amines and conversion to pentafluoropropionamides. This made it possible to prove the presence of 229a, 230 and 3-nitrofluoranthene (231a) in most samples of airborne particular matter taken in Upper Silesia482. 

Thus, for example, guanidine analogues guanoxyf n (79) and guanochlor (82) also possess antihypertensive activity. Guanoxyfen is synthesized by base-catalyzed condensation of phenol with chloroaceto-nitrile, followed by hydride reduction to amine 78. 

As carriers for ion exchangers they find application in HPLC. Cation exchangers are prepared by sulfonation, anion exchangers are prepared by nitration. Reduction to amines and alkylation, are achieved through quarternation and chloromethylation, respectively. 

In conclusion, the ionic bond as driving force for the formation of a heterobidentate bisphosphine seems a useful tool. Sulfonation of one ligand, and nitration followed by reduction to amine, may afford a relatively easy entry into this chemistry. Several... 

For the synthesis of bidentate ligands, supramolecular approaches have led to a renaissance in homogeneous catalyst discovery (Chapters 2, 4, 8, 9,10), and in a few cases even monodentate ligands have been modified in a supramolecular fashion (Chapter 8, Section 8.2). Combinations of monodentate ligands can be left to chance and in several instances this has led to successful, new catalysts [96]. Such heterocombinations can form spontaneously for steric or electronic reasons or the reactivity of the combinations can be different such that on certain occasions highly enantioselective catalysts are obtained. There are many ways to synthesize the desired heterocombinations selectively and the ionic modification outlined in Section 10.4 is only one of them since nitration (followed by reduction to amines) and sulfonation are robust methods, the ionic route may prove useful. Hydrogen bonding between different donor-acceptors (Chapters 2 and 8), Lewis add-base interactions (Chapter... 

The reactions of nitriles include reduction to amines and hydrolysis to acids. Both reactions have been discussed previously (Sections 18-7C and 18-7A). 

The synthesis of the tetracyclic intermediate 49 was therefore studied in the hope that it might further cyclize to the desired lycorine skeleton. Birch reduction of o,p-dimethoxyphenethylamine led to the amine 50 which was converted into 51, giving rise in turn upon hydrolysis to 49. Its structure rests on physical data. Ordinary methods for nitro group reduction seemed to also destroy the 289-nm chromophore, but hydrogen transfer (a-phellandrene and Pd/C) gave a product which analyzed for the product of nitro reduction to amine in 49, the mass spectrometric data also being in agreement. The product was, however, not affected by diazotization, and, on the basis of spectral data, was... 

In our selected example, Lehn and coworkers [80] reported the synthesis of a dynamic 12-member, template-directed imine library 1, obtained from the reversible condensation of three aldehydes (monomer set M, Figure 7.11), with four primary amines (monomer set M2, Figure 7.11) in buffered aqueous conditions, followed by irreversible reduction to amines 2 with sodium cyanoborohydride. The library was prepared in the presence of a large excess of M2, to prevent further condensation of an aldehyde onto the secondary amine product. A template-driven imine library 1 was prepared in the presence of the metalloenzyme carbonic anhydrase II (CAII). After the template-assisted, reversible dynamic reaction was complete, the reducing agent was added and the amine library 2 was produced (Figure 7.11). Without any... 

The influence of the cathode metal is much more manifest when acid electrolytes are employed than in alkaline reduction. In alkaline solution at copper electrodes, if we except the last-mentioned process, the rapidly occurring condensation of the first reduction phases—of the nitroso- and hydroxylamine body—always leads immediately to the azoxy-body and makes this appear to be the typical product of the alkaline reduction, which can in turn be further reduced. In acid solution this condensation takes place so slowly that the molecular rearrangement of the hydroxylamine and its further reduction to amine has time to take place alongside the formation of the azoxy-body and the reduction of the latter to the hydrozo-compound or benzidine.4... 

Reactions of Amides Because amides are the most stable acid derivatives, they are not easily converted to other derivatives by nucleophilic acyl substitution. From a synthetic standpoint, their most important reaction is the reduction to amines, which is one of the best methods for synthesizing amines. Amides are hydrolyzed by strong acid or strong base. Just as nitriles can be hydrolyzed to amides, amides can be dehydrated to nitriles. 

Triprotection of the 12-16-membered tetraazacycles was also achieved through organometallic approaches. Chromium(O) or molybdenum(O) tricarbonyl triamino complexes (e.g., 163-165) <1995JOM215> are substituted with acylhalogenides or aldehydes and N-monosubstituted products are obtained after oxidative deprotection in strong acid and acylamide/enamine reduction to amines <1995TL79>. 

Attempts to reduce benzaldehyde-o-nitrophenylhydrazone to benzaldehyde-o-hydroxylaminophenylhydrazone which on ring closure might form the dihydrobenzotriazine were not successful,70 as it was not possible to avoid the further reduction to amine. A similar situation is also found in the reduction of o-nitroanilines. 

An azomethine derivative is generally more easily reducible than the parent carbonyl compound and this can be exploited in cases where the equilibrium between the carbonyl compound and the azomethine derivative favors the former. By reduction at a potential at which the azomethine derivative, but not the carbonyl compound, is reduced, the azomethine is continuously removed from the equilibrium by reduction to amine as it is formed.91 This technique has been used for the preparation of 2-anilinomethylthiazole.276... 

Aromatic and aliphatic nitro groups Aromatic azo groups (reduction to amine)... 

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