Iron, and acid, reduction

When the compound to be treated contains more than one nitro group, the products of reduction depend upon the agents used. Thus, m-phenyl-enediamine is obtained by the iron and acid reduction of m-dinitrobenzene, while the alkaline sulfide reduction yields m-nitroaniline ... 

According to the proponents of the electron theory, such a small amount (about 1 per cent of total requirements) can be attributed to the difficulty in maintaining a practically homogeneous reaction mass Thus, the liberated hydrogen may be due to the reaction in Eq. (2) above, because the total iron surface is not in contact with molecules of nitrobenzene. It is rather remarkable, however, that such a high efficiency in proton or hydrogen-ion utilization is obtained in the iron and acid reduction. 

The reducers for iron and acid reductions are sometimes equipped with side and bottom cast-iron lining plates, which may be reversed or replaced, in order to protect the vessel against the continuous erosive action of the iron borings. Alternatively, the reducers may be lined partially or entirely with acid-resisting brick or tile. Such a protective coating lasts almost indefinitely and performs satisfactorily in service. 

Alkaline reductions are milder than the iron and acid reductions, and for this reason, modifications of this process find extensive use in technical operations. By utilizing alkali or metal sulfides, it is possible to control better the rate and degree of reduction. Although ammonium sulfide is sometimes used, sodium sulfide or sodium disulfide is most frequently employed. The sulfides of iron and manganese have also been found of value in reduction processes but thus far have not found widespread industrial applications. 

Redistillation gave a colorless oil, with a bp of 98 deg C at 0.11 mm/Hg. Anal. (Cl 1H1203) C,H. This intermediate ketone could be prepared by the Wittig reaction between piperonal and the derivative of triphenylphosphonium propyl bromide and dibutyidisulfide, followed by hydrolysis in a HCI/acetic acid mixture, but the yields were no better, Efforts to prepare this ketone by the iron and acid reduction of the appropriate nitrostyrene... 

Compounds containing two primary amino groups attached to a benzene ring can be prepared by the reduction of dinitro compounds and of nitroanilines, usually with tin or stannous chloride and hydrochloric acid or with iron and very dilute hydrochloric acid. / ara-diamines may also be obtained by the reduction of aromatic amino-azo compounds (e.g., p-aminodimethylanihne from methyl orange, see Section IV,78). p-Phenylenediamine may also be prepared from p-nitroacetanilide reduction with iron and acid yields p-amino-acetaniUde,.which may be hydrolysed to the diamine. 

The Zinin reduction is also usehil for the reduction of aromatic nitro compounds to amines in the laboratory. It requires no special equipment, as is the case with catalytic hydrogenations, and is milder than reductions with iron and acid. Usually ammonium or alkah sulfides, hydrosulftdes or polysulftdes are used as the reactant with methanol or ethanol as the solvent. 

Pour 50 cc. of concentrated sulfuric acid slowly into about 1 liter of water in an evaporating dish and add 50 g. of iron nails or turnings. When the action becomes slow heat the dish until the acid is practically all neutralized, as indicated by the fact that evolution of hydrogen ceases. Filter from the undissolved iron, carbon, silicon, and other residues, using a folded filter, and evaporate to crystallization. If the solution oxidizes appreciably in the operation additional iron and acid must be added to effect reduction. Oxidation will be indicated by a change in color from bottle green to a yellowish shade of green, or by the formation of a rusty precipitate. 

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. 

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. 

Wooden equipment is also used, particularly for the reduction of solid nitro compounds such as p-nitroaniline. These vessels are made of staves 2-3 in. in thickness, and the base is constructed of a double layer of 2-in. boards. Such tubs may range from 6-12 ft in diameter and up to a height of 12 ft. They are equipped with wooden exhaust stacks to vent the vapors and gases liberated during the reaction. The top of such a reducer contains a large opening through which the solid nitro body, iron, and acid are delivered, and it is provided with a removable cover. Bronze pipes are employed for the introduction of steam to such reducers. 

The method of sulfide reductions, although more expensive than iron and acid or catalytic reduction, has a wide field of application, particularly with respect to partial reductions and reductions in the anthraquinone series. Sodium sulfide, sodium hydrosulfide (the sulfhydrate of commerce), sodium polysulfides, ammonium sulfide, etc., are employed. Quite a number of benzene derivatives are normally reduced by this general method, and it is noteworthy that the first reduction of nitrobenzene was that by Zinin in 1842, using ammonium hydrosulfide. Where the presence of free... 

Tablets of Glyceryl Trinitrate, B,P. For small quantities of glyceryl trinitrate such as are found in tablets colorimetric methods must be employed, unless sufficient tablets are available for the material to be extracted with ether or ethanol for the macro- or a semi-micro-method. A method is given in the IJ.S.P. where tablets equivalent to about 5 mg of glyceryl trinitrate are reduced with Devarda s alloy after ether extraction and saponification. Smith adapted Anderson s method (above) to small quantities of material by using Nessler s reagent to determine the ammonia produced after reduction by reduced iron and acid with this modification only five tablets are needed for the assay. The details are ...

Colourless crystals m.p. 50 C, b.p. 301 C. Basic and forms sparingly soluble salts with mineral acids. Prepared by the reduction of 1-nitronaphthalene with iron and a trace of hydrochloric acid or by the action of ammonia upon l-naphlhol at a high temperature and pressure. 

N-phenylhydroxylamine, PhNHOH and further reduction can give azoxybenzene, azobenzene, hydrazobenzene and aniline. The most important outlet commercially for the nitro-compounds is the complete reduction to the amines for conversion to dyestufTs. This is usually done in one stage with iron and a small amount of hydrochloric acid. 

Ditrophenol, -nitropbenol, C H NOj. Colourless needles m.p. 114 C. Prepared as 2-nitrophenol. Reduction with iron and hydrochloric acid gives 4-aminophenol. 

It is usually prepared by the reduction of p-nitrophenetole with iron and hydrochloric acid. 

CfiHgNj. Colourless crystals m.p. 63 C, b.p. 2%TC. Turns brown in air. Prepared by a one-stage reduction of m-dinitrobenzene with iron and hydrochloric acid. 

Reduction products vary depending on the reducing agent, for example dinitrogen oxide is obtained with sulphurous acid, nitrogen is obtained when the gas is passed over heated metals (e.g. copper and iron) and ammonia is produced when the gas reacts with aqueous chromiumfll) salts. 

Reduction of aldehydes with iron and glacial acetic acid, for example ... 

Method B. Reduction with iron and hydrochloric acid. Place 40 ml. of water and 30 g. of grease-free iron filings (1) in a 750 or 1,000-ml. round-bottomed flask, and 25 g. (21 ml.) of nitrobenzene in a small beaker or conical flask. W arm the former on a water bnth at about 60°. Add... 

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