Aniline, formation Benzene, preparation

The most noteworthy reaction of azo-compounds is their behaviour on reduction. Prolonged reduction first saturates the azo group, giving the hydrazo derivative (C NH-NH C), and then breaks the NH NH linkage, with the formation of two primary amine molecules. If method (1) has been employed to prepare the azo-compound, these two primary amines will therefore be respectively (a) the original amine from which the diazonium salt was prepared, and (6) the amino derivative of the amine or phenol with which the diazonium salt was coupled. For example, amino-azobenzene on complete reduction gives one equivalent of aniline, and one of p-phenylene diamine, NHaCeH NH benzene-azo-2-naphthoI similarly gives one equivalent of aniline and one of... 

The technical preparation of crystal violet and of its methyl-free parent substance, parafuchsine, almost the oldest of the triphenylmethane dyes, is not so easily explained. As is well known, in this process aniline and p-toluidine are united by oxidation in an acid melt. (In the preparation of fuchsine itself, which contains a methyl group attached to one of the benzene rings, o-toluidine is an additional ingredient.) Although all the phases of this important synthesis have not yet been experimentally established, we may nevertheless explain it on the basis of a dehydrogenation similar to that involved in the formation of malachite green. Moreover, the union of several molecules of base proceeds exactly according to the principle on which indamines are formed (p. 321) (Bucherer). 

The nitration of aniline in the presence of a large amount of strong sulfuric acid results wholly in the formation of m-nitro-aniline, but the similar nitration of dimethylaniline gives principally a mixture of the ortho- and para-derivatives. Mono-methylaniline stands between aniline and dimethylaniline in respect to the orienting effect of its amino group it yields a considerable amount of the m-nitro- compound—and dimethylaniline is preferred for the preparation of tetryl. Commercial dimethylaniline contains a certain amount of monomethylaniline, from which it is extremely difficult to free it, and this in the manufacture of tetryl is converted in part into 2,3,4,6-tetranitro-phenylmethylnitramine, or m-nitrotetryl, pale yellow, almost white, crystals from benzene, m.p. 146-147.087... 

One of the side reactions is the formation of linear polyaryls, which may be considered to be formed by further reaction of the biaryl initially produced. From the high-boiling residue remaining after the removal of the biphenyl, formed from diazotized aniline, benzene, and alkali, p-terphenyl and quaterphenyl16 have been isolated and in the mixture formed in the preparation of 4-methylbiphenyl a hydrocarbon was found... 

Many synthetic methods have been developed for the preparation of quinolines and 1,2,3,4-tetrahydroquinolines due to the interesting biological properties of quinoline-type alkaloids. Most of the synthetic methods are based on the elaboration of aniline derivatives and, as for the synthesis of tetrahydroquinolines, reduction of the corresponding quinolines is the main approach. Only a few methods have been reported for the construction of the quinoline skeleton by N-C(8a) bond formation as the key step, such as oxidative cyclization of 2-(3-aminopropyl)benzene-1,4-diol 89 with K2[Fe(CN)e] (Scheme 42)... 

Iodine can be introduced into aromatic compounds by the action of the free halogen, if the reaction is carried out under conditions which bring about the removal of the hydriodic acid formed as the result of the substitution. For example, iodo-benzene is formed when benzene is heated with iodine and nitric acid, mercuric oxide, iodic acid, or other substances which react with hydriodic acid. Reactions of this kind are used in a limited number of cases only as a means of preparing iodo derivatives. Free iodine also converts aniline, C6H5.NH2, into substitution-products. In this case the hydriodic acid formed is removed, as the result of the formation of a salt of aniline, C6H5NH2.HI. 

Many modem composite materials are prepared by microemulsion methods. Polyaniline was prepared by one-step micellar chemical polymerisation of aniline with dodecyl benzene sulfonic acid via complex formation [297]. A transparent polyaniline suspension was made by dispersing polyaniline in m-cresol. Polyaniline composites blended with polymethyl methacrylate (PMMA) exhibits relatively high conductivity at low polyaniline volume fractions and keeps good mechanical properties equivalent to those of PMMA. It should be noted that most methods proposed for the preparation of new materials are at a laboratory level, however, a widespread commercial use can be predicted for the next decade. 

Pentaammineosmium(II) complexes have been prepared with a diverse array of -bound aromatic ligands (e.g., 2-8 in Fig. 2) including benzenes [20,21 ], ani-soles [22,23], anilines [24], phenols [25,26], naphthalenes, and other polyaromatic hydrocarbons [27-29], with yields typically >90%. Where convenient, the ligand is used in approximately a tenfold excess to minimize the formation of bi-nuclear impurities. However, if the aromatic substrate is precious, as little as 1.1 equivalents may be used, provided the reaction is carried out in water or methanol [23]. Carrying out the complexation procedure without a large excess of ligand should be avoided, as these conditions increase the possibility of forming stable binuclear arene complexes (see Fig. 2,1) [20]. 

In general, azo-, hydrazo-, and amido-compounds result from the electrolytic reduction of nitro-com-pounds. In this way Kendall obtained aniline from nitro-benzene, and Elbs and Haussermann prepared the normal reduction products of nitfo-phenol. The formation of azoxy-, azo-, amido-, or hydrazo-com-pounds was dependent upon whether acid or alkaline solutions were employed. If nitro-benzene is reduced in a concentrated acetic or formic acid solution, to which a few drops of concentrated sulphuric acid (to increase the conductivity) have been added, the corresponding salts of benzidene result a fact further confirmed by Lob. ... 

The great majority of quinolines and isoquinolines have been prepared by ring construction, instead of transformation of preexisting derivatives. They are obtained by variants of two main routes. The first route involves the cyclization of mono-substituted benzene rings, usually A-substituted anilines (Skraup, Doebner-von Miller, Knorr, Conrad-Limpach), and the second route involves the intramolecular condensation of o-disubstituted benzenes for the formation of the requisite pyridine ring (Friedlander, Pfitzinger reaction, etc.). 

Hofmann found only small amounts of aniline in coal-tar, but when he found benzene in the light oil distilled from the tar he prepared nitrobenzene and reduced this to aniline with nascent hydrogen from zinc and dilute acid, using as a test for benzene its conversion into nitrobenzene, the reduction of this to aniline, and the formation of a blue or purple colour with this and bleaching powder (see p. 184). Bechamp found that nitrobenzene is reduced to aniline by ferrous acetate but not by other ferrous salts, and also by iron filings and acetic acid. This was the foundation of the aniline dye industry, iron and hydrochloric acid being generally used. 

Wibaut JP (1917) For the formation of aniline from ammonia and benzene at high temperatures and in the presence of contact substances. Berichte 50 541-546 Thomas Cl (1985) Preparation of aromatic amines. Canadian Patent 553,988, 4 Mar 1958 Schmerling L (1960) Preparation of aromatic amines. US Patent 2,948,755, 9 Aug 1960 Squire EN (1975) Synthesis of aromatic amines by reaction of aromatic compounds with ammonia. US Patent 3,919,155, 11 Nov 1975... 

These nickel-eatalyzed aryl aminations found applieation in moleeu-lar materials with the preparation of l,3,5-tris(4-aminophenyl)benzenes or highly functionalized naphtidines (Figure 10.2), whieh possess interesting electronic properties potentially useful for molecular switches. Alternatively, the formation of five-, six-, and seven-membered rings, such as indoline, quinoline, indolizidine, and benzazepine derivatives was obtained with [(SIPr)2Ni] by intramolecular amination of appropriated chloro-anilines [eqn (10.10)]. ... 

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