Bechamp method

No N-alkyl or N-dialkyl anilines have been arsonated by the Bechamp method. With diphenylamine as starting material, 4-arsonodiphenyl-amine, 4,4 -diarsonodiphenylamine, and some arsinic adds were obtained in a combined yield of 18-20%.74... 

The older Bechamp method for iron oxide pigment production gives aniline as a co-product and is operated by Bayer in West Virginia. Nitrobenzene is reduced by reaction with iron filings in the presence of a hydrochloric acid catalyst. The iron is oxidized to the ferrous or ferric state, and the aniline-water mixture is separated from the iron-hydroxide sludge. The heavier aniline layer is removed and vacuum distilled to yield pure aniline. The yield is 90% to 95% of theoretical. The reactions are represented as follows138,255 ... 

The main method, both in the laboratory and in technical practice, for the introduction of an amino group into an aromatic compound, is nitration and reduction. Reduction of nitro compounds is accomplished by (1) catalytic hydrogenation, (2) iron reduction (Bechamp method), (3) sulfide reduction, or (4) zinc reduction in an alkaline medium. 

The Bechamp method can also be used in reducing the nitro derivatives of sulfonic acids. A typical example being the manufacture of metanilic acid and related substances [11]. 

The most widely used method of converting nitro compounds into an amine is the Bechamp method, which uses iron turnings in water containing a small quantity of hydrochloric acid. The reaction may be represented by the Eq. [5]. 

A large number of reducing agents has been used for the reduction of nitro groups. For example, the classical Bechamp method of reducing nitro compounds involves reaction with iron and acetic acid [27a]. 

Bechamp method, 129 Beckmann rearrangement, 94, 279 Benzilic acid rearrangement, 67-68 Benzoin condensation, 30 Bogoslovskii Reaction, 244 Boord synthesis, 17 Borsche synthesis, 244... 

The traditional technique of reducing nitro compounds with iron powder in dilute acid (Bechamps-Brimmeyr reduction) continues to be used for nitro compounds that are adversely affected by the catalytic reduction method with hydrogen. The list of examples includes aromatic nitro compounds carrying halogen substituents, especially if these are attached in ortho or para position to the nitro group. The solution containing only a small amount of acid (such as acetic acid) is almost neutral and allows iron to precipitate as Fe304. 

The property of being converted by energetic reduction into primary amines belongs to the nitro-compounds both of the aliphatic and of the aromatic series. Six atoms of hydrogen are required for the reduction of each nitro-group. In industry nitrobenzene is reduced, not with expensive tin, but with iron filings or iron powder according to the old method of Bechamp, which is still in use at the present time. The amount of hydrochloric acid indicated by the equation... 

In 1863, Bechamp 2 heated aniline arsenite with an excess of aniline at 190-200° and obtained a colorless solid which he thought was an acidic anilide. However, in 1907, Ehrlich and Bertheim 67 clearly demonstrated that the reaction, now known as the Bechamp reaction, involves the replacement of a nuclear hydrogen by the arsono group and that the compound produced is 4-aminophenylarsonic acid. Since its discovery the Bechamp reaction has been extended to include many phenols, substituted phenyl ethers, amines, and their various derivatives. In all, the literature contains more than sixty articles dealing with this method. 

Reduction with iron and water, with the addition of small amounts of acid (hydrochloric, sulfuric, or acetic acid, and occasionally mixtures of these). This neutral reduction method of Bechamp-Brimmeyr can be carried out oiJy with certain kinds of iron, notably gray-iron casting, which must always be tested pre. viously to establish its usabiL ty. In general, other kinds of iron are twt usable (many examples have been given). 

The reduction method described above, using iron in the presence of a small amount of add, was originated by Bechamp and Brimmeyr and is the most widely used technical reduction method. In general it runs very smoothly, provided that the following conditions are adhered to ... 

For the reduction of nitroarenes to aminoarenes by the catalytic hydrazine H-transfer reduction method, the classical hydrogenation catalysts Ni, Pd and Pt are most commonly used [1] [2]. In a more extended study [3] we were able to confirm previously reported observations [4] that these reductions can also be catalysed by modified iron oxides hydroxides. This method for the production of many aromatic amines offers several advantages compared to the conventional processes still employed in industry, such as the environmentally imfavourable Bechamp [5] and Zinin reductions [6]. It is an outstanding feature of the novel reduction method presented here that further reducible substituents in nitroazo compounds, such as... 

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 ... 

Reductions of mtroarenes. Nitroarenes were first reduced with iron and an acid by Bechamp in 1854. The use of iron in glacial acetic acid was reported in 1952 by Spring et al Owsley and Bloomfield have now made a systematic study of this method and conclude that it is a useful alternative to catalytic hydrogenation and is simpler to carry out than reductions with tin or tin(II) chloride with... 

Some chlorides of organic acids, e.g. benzoyl chloride, were prepared by Cahours by the action of phosphorus pentachloride on the acids, but not acetyl chloride, as he specifically says. Bechamp later used phosphorus trichloride. Gerhardt first prepared pure acetyl chloride by distilling anhydrous sodium acetate with phosphorus oxychloride, and by the action of acetyl chloride on anhydrous sodium acetate he discovered acetic anhydride. By similar methods the anhydrides of other monobasic organic acids were obtained, including mixed anhydrides. Gerhardt formulated the reaction ... 

Clearly the most important product from nitrobenzene is aniline it was first obtained by Otto Unverdorben in 1826 by distilling indigo and was named krys-tallin , since it easily forms crystalline salts with sulfuric add. The method introduced by Nikolai N. Zinin in 1841 of reducing nitrobenzene, later modified by Pierre LA. Bechamp employing with iron and hot hydrochloric add is still used on a large scale today, since the resultant iron oxides can be used as pigments. 

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