Acids azobenzene

With concentrated mineral acids azobenzene gives red salts, as may be shown by pouring hydrochloric acid on it. Addition of hydrogen leads to the re-formation of the hydrazo-compound. Oxygen is added on and the azoxy-compound formed by the action of hydrogen peroxide or nitric acid. The synthesis of asymmetrical aromatic azo-compounds from nitroso-compounds and primary amines was discussed above. 

Protein (40 mg) was dissolved in 2 ml 8 M urea solution, adjusted to pH 8.6 by the addition of 5 % methylamine, and jS-mercaptoethanol (20 pi) added. After 1 hr at room temperature, the protein was precipitated with acetone 1 N HCl (39 1, v/v) at -5°C, separated by centrifugation, and washed with acetone. The protein was dissolved in 2 ml of 25 % (v/v) aqueous acetic acid. Azobenzene-2-sulfenyl bromide (35 mg) was dissolved in 50% aqueous acetic acid (1 ml), and added to the solution of the reduced protein. After 30 min at 22-24°C, the protein derivative was freed of excess reagent by passage through a column of Sephadex G-25 (90 x 1 cm), equilibrated and developed with 0.2 M acetic acid, and lyophilized. 

Fig. 5.24. EDQ-diagram of the photoreaction of azobenzene in 66% sulfuric acid, azobenzene O, irradiation of cts-azobenzene.

Synonyms 4-Ami noazobenzene-3,4 -disulfonic acid 4-Amino-3,4 -disulfoazobenzene 2-Amino-5-[(4-sulfophenyl) azo]-benzenesulfonic acid 4-(4-Amino-3-sulfophenylazo) benzenesulfonic acid Azobenzene-3,4 -disulfonic acid, 4-amino-Benzenesulfonic acid, 6-amino-3,4 -azodi- Benzenesulfonic acid, 2-amino-5-((4-sulfophenyl) azo)- Benzenesulfonic acid, 4-(4-amino-3-sulfophenylazo) Cl 13015 Food yellow 2... 

Figure 4 (a) Chemical structure of tetra-acidic azobenzene (NN4A), coronene, and Ceo- (b) STM image of the coronene/Ceo/NNdA... 

Host-guest Polyallylamine [P-cyclodextrine], poly (acrylic acid) [azobenzene], poly(methacryUc acid) [azobenzene] Poly(L-aspartic acid) [adamantine] Dextran [carboxymethyl-, a-cyclodextrin, p-cyclodextrin]... 

Further nitration gives w-dinilrobenzene sulphonation gives w-nitrobenzene sulphonic acid. Reduction gives first azoxybenzene, then azobenzene and aniline depending upon the conditions. Used in the dyestufTs industry as such or as aniline. 

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. 

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. 

To prepare the hydrochloride, dissolve about 1 g. of the compound (which need not be perfectly dry) in about 8 ml. of alcohol. Add this solution to boiling dilute hydrochloric acid (10 ml. of the concentrated acid and 80 ml. of water). Boil for 5 minutes, filter the hot solution if necessary, and allow to cool. p-Amino-azobenzene hydrochloride separates in steel-blue crystals. Filter, wash with a little dilute hydrochloric acid, and dry. 

The reduction of the nitro group to yield aniline is the most commercially important reaction of nitrobenzene. Usually the reaction is carried out by the catalytic hydrogenation of nitrobenzene, either in the gas phase or in solution, or by using iron borings and dilute hydrochloric acid (the Bechamp process). Depending on the conditions, the reduction of nitrobenzene can lead to a variety of products. The series of reduction products is shown in Figure 1 (see Amines byreduction). Nitrosobenzene, /V-pbenylbydroxylamine, and aniline are primary reduction products. Azoxybenzene is formed by the condensation of nitrosobenzene and /V-pbenylbydroxylamine in alkaline solutions, and azoxybenzene can be reduced to form azobenzene and hydrazobenzene. The reduction products of nitrobenzene under various conditions ate given in Table 2. 

Nitroso compounds are formed selectively via the oxidation of a primary aromatic amine with Caro s acid [7722-86-3] (H2SO ) or Oxone (Du Pont trademark) monopersulfate compound (2KHSO KHSO K SO aniline black [13007-86-8] is obtained if the oxidation is carried out with salts of persulfiiric acid (31). Oxidation of aromatic amines to nitro compounds can be carried out with peroxytrifluoroacetic acid (32). Hydrogen peroxide with acetonitrile converts aniline in a methanol solution to azoxybenzene [495-48-7] (33), perborate in glacial acetic acid yields azobenzene [103-33-3] (34). 

In a 500-ml. round-bottomed flask equipped with a reflux condenser and a magnetic stirrer (Note 6) are placed 150 ml. of methanol, 150 ml. of 6N hydrochloric acid, and the total yield of 4,4 -bis(acetamido)azobenzene. The mixture is heated under reflux for 1.5 hours. The reaction mixture is cooled and the violet solid collected on a Buchner funnel (Note 7). The damp product is suspended in 500 ml. of water in a 1-1. beaker equipped with a stirrer, and the mixture is slowly neutralized by the addition of 2.5N sodium hydroxide. In the course of the neutralization, the salt dissolves and the free base separates. The 4,4 -diaminoazo-benzene is collected on a Buchner funnel, washed with water, and dried under reduced pressure. The yield of yellow product, m.p. 238-241° (dec.),is ll-12g. The over-all yield from/ -amino-acetanilide is 52-56%. 

We have noted above that benzocrowns may be nitrated quite readily. This approach was used in the formation of a photoresponsive bis-crown (see Sect. 3.8) wherein the nitrobenzo crowns reductively dimerize to the corresponding azobenzene. Kikukawa, Nagira and Matsuda have utilized 4-nitrobenzo-15-crown-5 in a somewhat different way during the synthesis of 4 -vinylbenzo-l 5-crown-5Nitration is effected using nitric acid in a mbcture of chloroform and acetic acid. 

These considerations show that caution must be exercised in applying of the Hammett equation to systems which are known to involve tautomeric equilibria, e.g. the pyridinecarboxylic acids or y-hydroxypyridines. If in such systems the experimental p L "values are linear in a, there is at least a strong suggestion that Krp is insensitive to the nature of the substituents. Some applications of these ideas in the azobenzene series have proved of considerable interest. ... 

Occasionally the product is contaminated with an impurity (1-2%), which appears as tiny red needles. This material has been tentatively identified as diethyl azobenzene-4,4 -dicarboxylate [Benzoic acid, 4,4 -azobis-, diethyl ester],... 

Azobenzene, 4,4 -dicarboethoxy [Benzoic acid,4,4 -azobis-, diethyl ester],... 

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