Aminoazobenzene, preparation

CgHgNa. While crystals m.p. 147 C, b.p. 267"C, darken rapidly in air. Prepared by reducing p-nitroaniline or aminoazobenzene. Oxidizing agents convert it to quinone derivatives, hence it cannot be diazotized with nitric acid. 

To prepare the hydrochloride, add about i g. of aminoazobenzene to 200 ml. of dilute hydrochloric acid and boil until nearly all the solid material has dissolved. Filter hot and allow to cool slowly. Aminoazobenzene hydrochloride separates as beautiful steel-blue crystals filter and dry. If a small quantity of the powdered hydrochloride is moistened with water and a few drops of ammonia added, the blue hydrochloride is converted back to the yellowish-brown base. 

Aminoazobenzene is a member of the large class of azo-compounds, all of which contain the characteristic grouping, C-N N-C. Azo-compounds are of considerable technical importance, as they are all coloured, and the majority possess considerable stability. They may be prepared by the following methods ... 

If either the o- or -position is occupied, only one isomer is obtained transformation to the mefo-position does not occur. This is a standard method of preparation of acyl-amino-ketones, or by a further hydrolysis of amino-ketones. The tendency, illustrated in this reaction, of groups to wander from the amino group to the nucleus, is also shown in previous reactions and in the preparation of aminoazobenzene from diazoamino-benzene (Preparation 456), of sulphanilic acid from aniline sulphate (Preparation 292), of o- and p-chloroacetanilides from acetochloranilide (Preparation 328), of o- and p-toluidine from methylaniline hydrochloride, and of 1 2 4-aminodimethylbenzene (2 4-xylidine) from dimethylaniline hydrochloride. 

Notes. (1) For preparations on a larger scale, mechanical stirring is recommended. (2) The crude compound may be employed in the preparation of p-aminoazobenzene. 

Polymers containing chromophores such as acridine and azobenzene have also been prepared by palladium-catalyzed amination according to two approaches [222-224]. The first approach involved the polymerization of monomers containing the chromophore. For example, 4-aminoazobenzene was condensed with 1,3-dibromobenzene (Eq. (39)) or 4,4 -dibromobiphenyl ether to form polymeric materials with Mw values of 9.0 x 103 and 19 x 103, respectively. Alternatively, polymers prepared by polymerization of 4-bromostyrene or copolymerization of styrene and 4-bromostyrene were coupled with N-phenyl-4-amino azobenzene. Substitution of the aryl bromides by the amino azobenzene unit was essentially quantitative when using P(tBu)3 as the ligand. 

The photoisomerization of all types of azobenzenes is a very fast reaction on either the singlet or triplet excited-state surfaces according to the preparation of the excited state, with nearly no intersystem crossing. Bottleneck states have lifetimes on the order of 10 ps. The molecules either isomerize or return to their respective ground states with high efficiency. So photoisomerization is the predominant reactive channel, and the azobenKnes are photochemically stable. Only aminoazobenzene-type molecules and pseudo-stilbenes have small quantum yields of photodegradation. 

A variety of quinoxaline derivatives have been prepared from 0-aminoazobenzenes the use of these intermediates again provides a method of unambiguous ring closure. Scheme 3 illustrates the preparation of the quinoxaline ester 32 similar ring closures take place with other carbonyl compounds, for example, acetophenone, with an active methylene group. ... 

The diazo-compounds form the starting point of numerous organic compounds, including the azo-dyes, the first representative of which (amino-azobenzene hydrochloride, aniline yellow ) was prepared and shown to be a dye by Mene. What was called aniline yellow is the oxalate of aminoazo-benzene (CeH5 N N-CeH4 NH2), introduced as a dye by Simpson, Maule, and Nicholson in 1863 its constitution was established by C. A. Martius and Griess, and the isomeric change of diazoaminobenzene into aminoazobenzene was explained by Kekule. ... 

In this series of bioassay experiments, several carcinogens failed to transform certain batches of hamster embryo cells, presumably because of a lack of endogenous enzymes required for the metabolic activation of these compounds. In short-term bacterial and mammalian cell mutagenesis systems, these enzymes are routinely provided by the addition of rat liver homogenates. As mentioned earlier, diethylnitrosamine and urethane, which failed to transform hamster embryo cells directly, were activated in a host-mediated in vivo-in vitro cell transformation assay in which the chemicals were inoculated intraperitoneally. In our laboratory, when A -2-acetylaminofluorene, 4-aminoazobenzene, auramine, diethylnitrosamine, 3-methoxy-4-aminoazoben-zene, Natulan, 2-nitrofluorene, p-rosaniline, and urethane were tested in the presence of hamster liver homogenates and appropriate cofactors, all except 4-aminoazobenzene gave positive results. The liver homogenates were prepared from hamsters that were not treated with enzyme inducers such as Aroclor 1254 or phenobarbital. 

Photoreactive and photochromic resins are easily prepared from SMA materials. For example, coupling 4-glycidoxychalcone " and a-(4-azidophenoxy) ethanol " to SMA gives potentially useful photosensitive coatings. Covalently bound 4-aminoazobenzene derivatives are useful in reversible hologram recording materials. " ... 

Acid Red 73 is a disazo dye prepared by diazotizing aminoazobenzene and coupling to G Acid. 

Some stilbene azo dyes are prepared by methods other than diazotization and coupling. Direct Orange 61, for example, is prepared by the condensation in alkaline solution of aminoazobenzene-m-sulfonic acid and dinitrostilbenedisulfonic acid. The exact structure of Direct Orange 61 is not known, but the presence of an azo linkage formed by... 

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