Bechamp reduction

It is worth noting, however, that up until fairly recently the reduction of aromatic nitrocompounds to the corresponding amines was commonly performed on an industrial scale, e.g. in the synthesis of azo dyes, with a mixture of iron and hydrochloric acid. This so-called Bechamp reduction has an E factor of ca. 15 compared to 1 for catalytic hydrogenation. 

Bechamp reduction org chem Reduction of nitro groups to amino groups by the use of ferrous saits or iron and dilute acid. ba shan ri dok-shon ... 

The starting compound for all triazinylaminostilbenes is 4,4 -dinitrostilbene-2,2 -disulfonic acid [128-42-7], which is obtained by oxidizing 4-nitrotoluene-2-sulfonic acid with aqueous sodium hypochlorite in the presence of sodium hydroxide or, more recently, by atmospheric oxidation in an aqueous ammoniacal medium [39], The Bechamps reduction using iron filings etched with hydrochloric acid yields 4,4 -diaminostilbene-2,2 -disulfonic acid [81-11-8] (DAS). 

The traditional treatment of nitrobenzene (1) with iron and acid, called Bechamp reduction, was employed almost exclusively in the production of aniline (2) and many aromatic amines until the 1960s1,2 (Scheme 1). The reduction is straightforward, and can also be achieved by catalytic hydrogenation, sodium sulfide reduction and zinc reduction with caustic soda. Nitrotoluenes and nitroxylenes are hydrogenated under pressure over a nickel catalyst supported on kieselguhr. The sulfide reduction is useful in selective reduction, such as of m-dinitrobenzene to m-nitroaniline. 

Sulfide reduction has an even broader selectivity profile than catalytic hydrogenation or the Bechamp reduction and enables the chemoselective reduction of nitro compounds in presence of C=C, azo, or other nitro groups. The method is insensitive to by-products and high levels of impurities. Depending on pH, different reduction agents with the following stoichiometries are applicable ... 

Catalytic hydrogenation Bechamp reduction Sulfide reduction... 

Explanations of the mechanism of iron and acid (Bechamp) reductions can be made on the basis of observed chemical phenomena as well as electronic theory. Both explanations are useful in providing a better understanding of the reduction process and in providing guides for efficient industrial operations. 

This reaction is related to the Bechamp Reduction and Hinsberg Oxindole Synthesis. 

A tentative mechanistic detail of the Bechamp reduction is also illustrated below. 

Reduction of nitroaromatics with iron (Bechamp reduction) Additive reduction with elimination... 

It is better to prevent waste generation than to treat or clean up waste after it has been created. The earlier messy Bechamp reductions using Fe-HCl and generating a highly acidic waste sludge are replaced by clean catalytic processes using suitably designed multiphase reactors (Section 1.3 and Chapters 7A and 8). 

Catalytic processes are superior to processes that use stoichiometric reagents (Bechamp reduction cited earlier). There is a continuous improvement in catalysts. Many acid-catalyzed reactions (esterifications, hydrations, alkylations) have been replaced by benign ion exchange resins in the H form (Wasker and Pangarkar 1992, 1993). The newer catalysts are not only more selective but also more active in enhancing reaction rates. In some cases, for instance, replacement of mineral acids by ion exchangers allows the use of low-cost material of construction and facile separation/recycle of the catalyst while simultaneously eliminating ultimate neutralization of the product by a base. 

Baumann (see Schotten-Baumann Reaction) Baylis-Hillman Reaction Bechamp Reduction Beckmann Fragmentation Beckmann Rearrangement... 

COCH3 Preparation by reduction of 4-chloro-2-hydroxy-5-ni-tro-acetophenone with iron powder in dilute acetic acid at 95° (93%) [1784] (Bechamp reduction). 

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