Preparation of Aniline

Introduction. The preceding experiment illustrated the preparation of amines by the replacement of the halogen atom by the amino group. The present experiment illustrates the preparation of amines by the reduction of nitro compoimds. The reduction of the nitro compounds is analogous to the reduction of nitric acid to ammonia  

In the reduction either tin or iron and hydrochloric acid may be used  

The use of tin involves a number of difficulties. The chlorides of tin produced in the presence of an excess of hydrochloric acid give chlorostannic acid, which combines with aniline and some other arylamines to form complex double salts as shown in equation (4). In order to decompose these salts alkali is used. A great excess must be employed in order to change the stannic hydroxide, which i,s formed, to soluble sodium stannate  

SnCh + 2 HCl 2 CbHbNHs + HjSnCh (C6HbNH2)2 HjSnCle -f 8 NaOH 

Comparison of tin and iron as reducing agents. Tin is traditionally used for the preparation of aniline in the laboratory, since it gives good yields. Iron is employed industrially as a reducing agent. The amount of hydrochloric acid used is less than 5 per cent of the 

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Nitrobenzene is a pale yellow liquid, having a b.p. 210 , and dy 1 20. It has an odour which is similar to that of almonds, and which is therefore often confused with that of benzaldehyde. Nitrobenzene is used chiefly for the preparation of aniline. 

Filter the dried ethereal solution, and then distil off the ether from a small flask, using precisely similar apparatus and the same method as those described in the preparation of aniline (Fig. 64, p. 163 see also Fig. 23(E), p. 45) and observing the same precautions. When the ether has been removed, fit the distilling-flask to a short air-condenser, and distil the benzonitrile, collecting the fraction boiling between 187" and 191°. Yield, 16-5 g. (16 ml.). 

Catalytic hydrogenation processes in which copper is the catalytic agent have also been recently introduced into industrial practice for the preparation of aniline from nitrobenzene. 

Iodine is used in various forms in medicine—e.g. tincture of iodine, liquor iodi, iodized cotton, iodized wine, iodized water, oils and syrups iodides of potassium, mercury, iron, arsenic, lead, etc. and as methyl iodide or di-iodide iodoform, CHI3 ethyl iodide, C2H5I iodole, C4I4.NH aristole etc.—largely for external application as an antiseptic. Some iodides are used in photography, and in analytical operations and a considerable amount of iodine is used in the preparation of aniline dyes. 

The preparation of aniline nitrate is fully described on p. 375 under the preparation of diazobenzene nitrate. The crude product therein obtained is recrystallised by dissolving in a little absolute alcohol and precipitating therefrom with ether. The preparation and purification of aniline hydrochloride are exactly similar. 

Nitrobenzene is a pale yellow liquid, b.p. 208.0°, which is poisonous and has an almondlike odor closely resembling that of benzaldehyde (which is not poisonous). It is used as a component of certain Sprengel explosives and as a raw material for the preparation of aniline and of intermediates for the manufacture of dyestuffs and medicinals. Its preparation, familiar to every student of organic chemistry, is described here in order that the conditions for the substitution of one nitro group in benzene may serve us more conveniently as a standard for judging the relative ease and difficulty of the nitration of other substances. 

When reduction is complete, a complex amine chlorostannate may separate from which the amine is liberated by basification, using enough alkali to dissolve the tin hydroxides formed (e.g. the preparation of aniline, Expt 6.48). 

Nitrobenzene is a highly toxic, pale, yellow liquid, having a specific smell of bitter almonds. It melts at +5.7°C, and boils at 210.9°C. It was first obtained by Mitscherlich [1] in 1834. The compound is widely used in organic industry as a starting material for the preparation of aniline, benzidine and other intermediates... 

In the industrial preparation of aniline, the iron is added gradually and less water is used.2 The yields obtained are practically quantitative about 110 kilograms of pure aniline from 100 kilograms of benzene. The aniline is vacuum distilled in batches of 10,000 to 30,000 kilograms, the heat being supplied by a system of steam coils inside the kettle. 

Upon reduction, the mononitrotoluenes act differently, according to the metal used in the reduction. It iron be used with hydrochloric acid, the corresponding toluidin is produced, the reaction being analogous to the preparation of aniline. If zinc and hydrochloric acid is employed, a chlortolmdin is produced. 

Preparation of Aniline.—In preparing aniline, nitro benzene is usually reduced by means of tin and hydrochloric acid or iron and hydrochloric acid, the latter being the commercial process. In the reaction with tin, molecular proportions of the tin and acid must be used and the hydrogen produced must be sufficient for the reduction of the nitro benzene. The reaction proceeds as follows ... 

Aminoazo Benzene from Nitroazo Benzene.— Another method of preparing aminoazo compounds is analogous to the preparation of aniline, i.e.f by the reduction of the corresponding nitro compound. When azo benzene is nitrated we obtain nitro azo benzene and this on reduction yields amino azo benzene. 

Which of these methods can be applied to the preparation of aniline Of benzylamine ... 

B) Preparation of Aniline (Sm.). (Use of tin as a reducing agent.) Place 3 ml of nitrobenzene and 14 ml of concentrated hydrochloric acid in an eight-inch tube, and arrange for reflux with a micro condenser. Add in small portions 6.5 g of granulated tin. The reaction is controlled by the rate of addition of the metal. Shake the tube from time to time. When all the tin is added, boil gently for half an hour until the odor of nitrobenzene disappears. 

D) Preparation of Aniline (M.). (Use of tin as reducing agent.) Place 30 ml (35 g) of nitrobenzene and 65 g of tin in a flask. Provide with a reflux condenser, and add in 10-ml portions, over a period of half an hour, 140 ml of concentrated hydrochloric acid. The reaction should be vigorous it can be controlled by the rate of addition of the acid and by immersing the flask momentarily in a pail of cold water. The rate of addition can be... 

The synthesis of aminobenzenes from reduction of nitrobenzenes was beyond any doubt a pivotal discovery, and the original preparation of aniline by Nikolai Zinin is still kept in the Museum of Kazan School of Chemistry (Russia) http //www.kazan.ru/tat ru/universitet/ museums/chmku/eng/s2.php... 

The reactions below are well-known methods for the preparation of anilines from compounds other than aromatic amines. 

In the classical student preparation of aniline - granular tin and hydrochloric acid is just as satisfactory as the more expensive stannous chloride because the product is isolated, after alkalinization, by steam distillation. However, for reduction of anthraquinone to anthrone the SnCU-HCl-AcOH method (see Stannous chloride) seems preferable to the Sn-HCl-AcOH method because it eliminates a troublesome filtration of the hot acid solution and because the yield is 10% better. In those cases where the metal alone has been used it is not clear whether the chloride was tried and found unsatisfactory or merely not tried. A procedure for the reduction of anisoin to desoxyanisoin specifies use of 200-mesh tin in 40% excess of the theory, and a note states that reduction in the amount of metal reduces the yield. 

Scheme 6.2 A multicomponent reaction for the preparation of aniline derivatives. Primary amines tend to yield 2-substituted anilines 36a, while sterically demanding secondary amines form predominantly 4-substituted anilines, 36b.

The cascade reaction for the preparation of anilines is particularly well suited to the synthesis of potential ligands, as is illustrated by the scorpion ligand A,A-4-tris(pyridin-2-ylmethyl)aniline (37), which forms a range of Cu complexes with widely varying solid-state structures.Clearly, from the metal coordination geometries illustrated in Figure 6.9, Horning-crown macrocycles may fulfill similar roles. 

Electrolytic oxidation of anthracene in 20 per cent sulfuric acid solution with 1 per cent of vanadium pentoxide present is carried out at 80° C. with lead electrodes and a current density of 300 amperes per square meter at 1.6 volts. Good yields have been claimed 10 for this process. Air under pressure has been used for the oxidation of anthracene in the form of dispersions in aqueous ferric sulfate solutions,20 or as a solution iu pyridine or dispersion in aqueous alkaline solutions preferably in the presence of catalysts 21 of copper, cobalt, nickel or lead compounds. Vanadium compounds have been found more active than chromium compounds for use as oxidation catalysts in the form of suspensions in the liquid phase, as in the preparation of aniline black.22 Anthracene suspended in water or dilute sulfuric arid or dissolved in a solvent as acetone is oxidized with ozone, or ozonized oxygen at ordinary temperatures.28... 

The same principle of extraction by a solvent is involved in the laboratory preparation of aniline by reducing nitrobenzene in which method the product is steam distilled from the reaction mixture, giving a little aniline with a relatively large volume of water. These are best separated by shaking the mixture with a volatile solvent in which the aniline dissolves (e.g. ether) the lower aqueous layer is separated from the ether layer. The ethereal extract is then dried by allowing it to stand over anhydrous calcium chloride to remove the water carried by ether. Finally, distillation of this dried extract yields aniline by removal of the volatile solvent, ether. 

When a volatile substance is distilled with water, the substance is said to be steam-distilled if water comes over in the distillate. Steam distillation is not feasible if the substance reacts rapidly with water. It is especially useful under one or more of the following conditions (1) When the presence of solid matter makes ordinary distillation, filtration and extraction impractical as, for example, in the preparation of aniline (2) when the presence of tarry matter makes extraction with an organic solvent messy and inconvenient, as in the case of preparation of phenol ... 

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