Aniline industrial preparation

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. 

Methyl iodide—CH Z—142-—a colorfesa liquid, ep. gr. 2.237 boils at 46 (113 F.) bums with difficulty> producing violet vapor of iodine. It 18 prepared by a process similar to that for obtaining the bromide and IB ua in the aniline industry. 

One may recall that aniline was prepared from the coal tar residues of the gas industry in the first half of the nineteenth century, and later played later a fundamental role in the development of organic chemistry and the chemical industry. First, aniline dyes replaced dyes from natural sources. Then coal tar dyes found use in medicine (to stain tissues), andP. Erhch discovered the selective toxicity of these compounds. This initiated the chemical production of medicines, and the establishment of the pharmaceutical industry. 

Benzoquinone ( quinone ) is obtained as the end product of the oxidation of aniline by acid dichromate solution. Industrially, the crude product is reduced with sulphur dioxide to hydroquinone, and the latter is oxidised either with dichromate mixture or in very dilute sulphuric acid solution with sodium chlorate in the presence of a little vanadium pentoxide as catalyst. For the preparation in the laboratory, it is best to oxidise the inexpensive hydroquinone with chromic acid or with sodium chlorate in the presence of vanadium pent-oxide. Naphthalene may be converted into 1 4-naphthoquinone by oxidation with chromic acid. 

Michler s ketone is prepared industrially by the interaction of phosgene (COCl,) and dimethyl aniline. 

In the Bnchamp process, nitro compounds are reduced to amines in the presence of iron and an acid. This is the oldest commercial process for preparing amines, but in more recent years it has been largely replaced by catalytic hydrogenation. Nevertheless, the Bnchamp reduction is still used in the dyestuff industry for the production of small volume amines and for the manufacture of iron oxide pigments aniline is produced as a by-product. The Bnchamp reduction is generally mn as a batch process however, it can also be mn as a continuous (48) or semicontinuous process (49). 

In the former Soviet Union much use is made of industrial by-products to prepare acid inhibitors. The PB class is obtained by treating technical butyraldehyde with ammonia and polymerising the resulting aldehyde-ammonia. PB-5, for example, with O-Ol-O-15% of an arsenic salt is used in 20-25% HCl. A mixture of urotropine (hexamethyleneimine, hexamine) with potassium iodide, a regulator and a foaming agent is the ChM inhibitor. BA-6 is prepared from the condensation product of hexamine with aniline. A more recent development is the Katapin series which consists of /7-alkyl benzyl pyridine chlorides Katapin A, for example, is the /7-dodecyl compound. 

Aniline and other aromatic amines are valuable industrial raw materials. They form an important starting point from which many of our dyestuffs, medicinals, and other valuable products are prepared. For example, you have used the indicator, methyl orange, in your laboratory experiments. Methyl orange is an example of an anQine-derived dye, although it is used more as an acid-base indicator than for dyeing fabrics. The structure of methyl orange is as follows ... 

The largest use of aniline is for the preparation of chemicals used in the ruhher industry. 

The next milestone in the development of organic synthesis was the preparation of the first synthetic dye, mauveine (aniline purple) by Perkin in 1856 Perkin, 1856, 1862). This is generally regarded as the first industrial organic synthesis. It is also a remarkable example of serendipity. Perkin s goal was the synthesis of the antimalarial drug quinine by oxidation of N-allyl toluidine (Fig. 2.4). 

For more than a century, stoichiometric methods were presumed in the preparation of benzonitriles in laboratory and industry. These particularly include the Rosenmund-von Braun reaction of aryl halides, the diazotization of anilines and subsequent Sandmeyer reaction, and the ammoxidation. Because of (over)stoichiometric amounts of metal waste, lack of functional group tolerance, and harsh reaction conditions, these methods do not meet the criteria of modern sustainable synthesis. 

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. 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

August Wilhelm von Hofmann, 1818-1892. German chemist who served for many years as the first professor at the Royal College of Chemistry in London Founder of the aniline dye industry He devised the simple process of preparing aniline by ultrabng benzene and reducing the nitrobenzene. He was one of the founders of the Deutsche Chem-lsche Gesellschaft, and was elected president fourteen times. See also ref. (65). 

Wester et al (Ref 24) patented an industrial method of preparation of diarylamine, and more particularly of DPhA. Essentially the process comprises heating aniline in an autoclave at pressures betw 100 and 200psi, in the presence of ferric chloride catalyst in an amount betw 0.3% to 8.0% by wc of the aniline used. Yields as high as 58.8% were reported after heating for only 8 hrs at l60psi... 

Such evaluation should be adopted in all the simpler preparations. In this way the student will become acquainted with the elements of costing which play such an important part in his later life in the factory. He should hardly wait until he enters the factory to appreciate the cost of such common substances as sulphuric acid, benzene, aniline, naphthalene he should be able to estimate roughly the cost of derivatives such as dinitrobenzene, p-nitroaniline, etc. Even should he not take up the industrial side of his profession, he should be acquainted with the relative value of the more common products, and trained to decide for himself whether, for example, it would be more economical to extract with ether or benzene, taking into consideration the relative efficiencies of the two processes. 

Aniline is a compound used in the synthesis of insecticides, chemical brighteners, and dyes and is a by-product of the petroleum, paper, and coal industries. The photocatalytic oxidation of aniline was studied by Sanchez et al. (1997). The reaction was found to follow Langmuir-Hinshelwood kinetics. The adsorption rate constant and the reaction rate constants were also reported. Higher yields were reported for acidic conditions and values near the pH at the point of zero charge (pHpZC) of Ti02. The rate of photocatalytic oxidation was also found to increase with the addition of small amounts of Fe. Hydroquinone is the main intermediate formed from the reaction. Photocatalytic reactions were carried out in a 130-cm3 cylindrical Pyrex cell. Medium-pressure mercury lamps provided UV light. Initial concentrations of 1.0 x 104 and 2 g/L were prepared. The pH of the solutions was adjusted and reactions were carried out for 15 min. Concentrations of aniline and byproducts formed were determined by HPLC. 

In the industrial manufacture of acid azo dyes usually aniline derivatives are used as the diazo components. The coupling components for orange to blue shades are commonly aniline, naphthol, naphthylamine and aminonaphthol derivatives, whereas phenylpyrazolones are much used for preparing dyes in the yellow and orange shades. 

A large number of azines were produced in the early decades of industrial dye manufacture. The synthesis was an all-in operation involving a sequence of oxidation reactions. Mauveine (3), for example, was prepared by oxidizing aniline containing o- and /i-toluidines with potassium dichromate in cold dilute sulfuric acid solution. 

When reduced by electrolysis, nitrobenzene and its homologues yield the same products as may be obtained by the various chemical methods of reduction. Aniline, azobenzene, azoxybenzene, hydrazobenzene, and -amino-phenol, as well as phenylhydroxylamine, can thus be obtained from nitrobenzene, and most, if not all, of these products could be prepared satisfactorily on an industrial scale by electrolysis, by adjusting the manner of working so that economy of energy is combined with maximum yields. Many of these products demand a comparatively high price, so that low power cost is not so important in this class of manufacture as high percentage yields. 

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