Aniline from azobenzene

The use of hypervalent iodine reagents for heteroatom-heteroatom bond forming reactions is well established in the context of classical oxidation chemistry [1-11]. For example, oxidations of anilines to azobenzenes, thiols to disulfides, and sulfides to sulfoxides with aryl-A3-iodanes were documented decades ago [1-5]. During the last ten years, particular attention has also been given to oxidative transformations of compounds derived from heavier elements, including the interception of reaction intermediates or initially formed products with external nucleophiles. A second important development is the utilization of sulfonyliminoiodanes, ArI = NS02R, for heteroatom-nitrogen bond formation, especially for imidations of sulfur, selenium, phosphorus and arsenic com-... 

The vapor-phase pyrolysis of phenyl azide yields azobenzene in 72 % yield . The pyrolysis in aniline solution leads to the production of dibenzamil , identified as an azepine by modern techniques in benzene and p-xylene, the major products are azobenzene and aniline, presumably originating from reactions of PhN in hydrocarbon solvents the thermolysis produces aniline, alkyl-anilines, azobenzene and polymer . It has been shown that aniline and iV-alkylanilines arise from triplet state nitrene reactions with the solvent. In the gas-phase thermolysis of phenyl azide at low pressures aniline and azobenzene are the major products whereas at higher pressures the formation of l-cyano-1,3-cyclopentadiene (or 2-anilino-7H-azepine in the presence of aniline) predominates . It was deduced that aniline and azobenzene arise from triplet nitrene reactions and that at high pressures, a hot singlet nitrene is formed, which undergoes intramolecular insertion to form an azocyclopropene intermediate, viz. 

In 1955, Terent ev and Mogilyanskii reported the catalytic oxidative coupling of aniline to azobenzene with a yield of 88%, mediated by copper chloride in pyridine (which acts as both a metal ligand and solvent) in the presence of molecular oxygen [1]. This system was subsequently used for the generation of various conjugated and nonconjugated main-chain aromatic azo polymers from primary aromatic diamines [2]. In contrast, the use of CUCI-O2 with phenol produces tars [3] as a result of the inherent properties of this reactant. Indeed, while the metal salt produces iV-centered aniline radicals that dimerize to form azobenzene... 

Bruni demonstrates in an analogous way the connection between crotonic acid and butyric acid the trans-form is indicated for crotonic acid and the cis-form for isocrotonic acid. He further deduced, from the isomorphism of stilbene, benzal aniline and azobenzene with dibenzil, the transconfiguration of these compounds x-ray examination clearly confirmed the trans-form for stilbene. If it is possible in this way to establish the position of the unknown double bond in a known aliphatic chain, it is possible conversely, from a knowledge of the olefine configuration, to determine the configuration of the paraffin crystallizing with it. 

It should be mentioned that polymers that behave in a similar way to PANl can also be prepared from compounds other than aniline (e.g., from azobenzene [201]). Substituted anilines—especially the formation and redox behavior of poly(o-tolu-idine) (POT)—have been studied in detail [328-343]. 

Stem, M. K. Cheng, B. K. M. Process for preparing substituted aromatic amines via reaction of aromatic azo compounds with alcohols. US Patent 5382691,1995 Chem. Abstr. 1995,123, 82929. Stem, M. K. Cheng, B. K. M. Preparation of substituted aromatic amines from azobenzenes and anilines. PCX Int. Appl. WO 9425425,1994 Chem. Abstr. 1995,122,105400. 

These colours were phenylene brown (also called Manchester, Martius or Bismarck brown), naphthalene yellow (Martius yellow), and induline, the latter made from azobenzene, aniline and the hydrochloride salt of aniline. For this work Caro received a share of the profits, depending on the amount of sales. In return for a payment of 500 Gulden he agreed not to... 

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... 

Dissolve 5 g. of finely-powdered diazoaminobenzene (Section IV,81) in 12-15 g. of aniline in a small flask and add 2-5 g. of finely-powdered aniline hydrochloride (1). Warm the mixture, with frequent shaking, on a water bath at 40-45° for 1 hour. Allow the reaction mixture to stand for 30 minutes. Then add 15 ml. of glacial acetic acid diluted with an equal volume of water stir or shake the mixture in order to remove the excess of anihne in the form of its soluble acetate. Allow the mixture to stand, with frequent shaking, for 15 minutes filter the amino-azobenzene at the pump, wash with a little water, and dry upon filter paper Recrystallise the crude p-amino-azobenzene (3-5 g. m.p. 120°) from 15-20 ml. of carbon tetrachloride to obtain the pure compound, m.p. 125°. Alternatively, the compound may be recrystaUised from dilute alcohol, to which a few drops of concentrated ammonia solution have been added. 

A range of products was obtained from aniline including those from oxidative coupling (azozybenzene, azobenzene, and benzidine), and phenazine by dimerization (Chan and Larson 1991). Oxidation of m-phenylenediamine was initiated by the oxidation of two molecules to produce an A-phenyl-2-aminoquinone-imine that reacted with m-phenylenediamine to produce 2-amino-5-phenylaminoquinone-imine after further oxidation (Kami et al. 2000). 

By Dismutation.—Hydrazobenzene (1-2 g.) is melted in a test tube over a small flame. The orange-red liquid thus produced is carefully heated until the aniline which has been formed begins to boil. On cooling, a semi-solid mixture of red azobenzene and aniline is obtained. The aniline can be shaken out with water and identified by means of the bleaching powder reaction. The azobenzene may be recrystallised from alcohol as described above. If it is desired to isolate the aniline also, when larger amounts of hydrazobenzene are used, the base is separated from the azobenzene by means of dilute acetic acid. From the solution of its acetate the aniline is then liberated with concentrated alkali hydroxide solution, extracted with ether, and purified in the manner already described. 

The products obtained by reacting phenylnitrene with 3-methyl-1-butene in benzene solution as has been described in the experimental section was analysed by gas chromatography. It gave five peaks from A to E as shown in Figure 5- Comparing the retention times of these peaks with those which were obtained by the method described in the previous section or with the compounds obtained by known methods, peaks A, B and D correspond to those of aniline, aziridine and azobenzene, respectively. 

Figure 6 shows the gas chromatogram of the reaction products obtained by the ultraviolet irradiation to phenylazide dissolved in 3-methyl-1-butene. It has four peaks from a to d. Peaks a and c agree with those of aniline and aziridine in their retention times, respectively. In this case, the peak due to azobenzene did... 

In the reaction profile shown in Figure 1 (similar to that shown by Smith et al. (10)) the initial product was azoxybenzene. However this figure is deceptive firstly azoxybenzene may be produced by a non-catalyzed reaction between nitrosobenzene and phenyl hydroxylamine (10), secondly the figure does not show the mass balance. Indeed at 10 min when all nitrosobenzene has been removed from the solution the amount of azoxybenzene formed was 18.6 mmol, equivalent to 37.2 mmol of reacted nitrosobenzene. Therefore, 42.8 mmol of the original 80 mmol of nitrosobenzene (53.5 %) were unaccounted for. It is possible that the missing mass is in the form of phenyl hydroxylamine in solution, which continues to disproportionate to produce aniline and nitrosobenzene and subsequently azoxybenzene and azobenzene. However as we shall subsequently discover this interpretation is unsustainable. 

It can be seen from this figure that the steady state production of nitrosobenzene is preceded by an induction period, in which aniline is the main product. Further, small amounts of azobenzene and azoxybenzene are formed throughout the reaction. The existence of an autoredox reaction implies that a selectivity of 100% from nitrobenzene to nitrosobenzene is impossible. After the induction period the selectivity of nitrobenzene to nitrosobenzene becomes above 90% of the reduction products. The extent of conversion of nitrobenzene is also time dependent. In the steady state situation about 20% of the nitrobenzene is converted, after an initial conversion of 65%. 

The qualitative application is illustrated by the approximate location of E°w for the azobenzene/aniline couple on redox ladders constructed by Schwarzenbach et al. (e.g., Figure K.3 in Reference 120). The estimate, around -0.1 V vs. NEIE, comes from electrochemical studies that report non-Nemstian dependence of E1/2 on pEI and additional evidence for the non-reversibility of this reaction (8,121). 

A number of by-products may be isolated from sodium stannite reductions. In addition to benzene, aniline gives phenol, azobenzene, phenyl azide, and phenylhydrazine.107 10 108 109 The danger of hydrolytic cleavage in alkaline media, previously discussed in connection with the... 

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. 

In the reduction of nitrobenzene in a 2% aqueous sodium-hydroxide solution, according to previous publications, azoxy-benzene is formed at platinum and nickel electrodes, azobenzeno at lead, tin, and zinc cathodes, and aniline at copper cathodes especially in the presence of copper powder. It was found that, in an unchangeable experimental arrangement, a cathodo potential of 1.8 volts, as measured in connection with the deci-normal electrode, could be carried out with all the chosen cathodes and additions. At this constant potential, by using different metals and adding various metallic hydroxides, the whole reduction was carried out and the nature and quantity of the reduction products determined in each case. It turned out that the emphasized differences in the results disappeared and that, with an equal potential of all cathodes, similar yields of azoxybenzene and aniline and traces of azobenzene resulted. The cathodes were of platinum, copper, copper and copper powder, tin, platinum with addition of stannous hydroxide zinc, platinum with addition of zinc hydroxide, lead, platinum with addition of lead hydroxide, and nickel. The yields of azoxybenzene varied from 41-65% of aniline 23-53%. 

Chry sordine (Di amino azobenzene or 4-Phenylazo -m-phenylene diamine Hydrochloride) [called 2,4 -Diamino-azobenzol 4-Benzolazo-phenylenediamin -(I.3) or Base des Chrysoidins in Ger]. C Hg. NiN.CgHgOSfHj) mw 212.25. N 26.40% yel ndls (from hot w), mp 117.5° s l rlc, eth, chlf, benz or aniline si sol in hot w. It forms numerous salts which are cryst comds. The Hydrochloride (also called Chrysoidine Y or Chrysoidine Extra), Cl H 2 4 HCl, red-bm powd or large, black shiny crysts having a green luster, is the commercial product. The Dibydrochloride, col crysts (from ale), dec at 222°. Other props methods of prepn are given in Ref 1... 

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