Aminoazobenzene from aniline

Problem 18.55 Using any aliphatic and inorganic reagents, outline the syntheses of (a) m-HOC(,H4CH, from toluene, (b) 4-bromo-4 -aminoazobenzene from aniline. M... 

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. 

Primary and secondary amines react with diazonium salts to form initially the N-azo derivatives, e.g., diazoaminobenzene, C,HjNHN= NC,Hs, from aniline and benzenediazonium chloride. In the presence of acids, these compounds isomerize to the corresponding p-aniinoazo derivatives for example, the above compound goes to p-aminoazobenzene, p-NH2CjH4N = NC6Hs. If the para position is not free, isomerization to the ortho position occurs. The isomerization may proceed by a fission of the diazoamino compound to the progenitors, which then undergo... 

Reaction.—Make a solution of 4 grams stannous chloride in TO c.c. cone, hydrochloric acid, add 2 grams aminoazobenzene, and boil for a few minutes. On cooling ciystals of the hydrochlorides of aniline and yi-phenylenediamine separate out. The liquid is filtered and washed with a little cone, hydrochloric acid to remove the tin salts. If the precipitate is dissolved in water and made alkaline with caustic soda, a mixture of liquid aniline and solid/-phenylenediamine is precipitated, from which the former may be removed by filtering, washing, and draining on a porous plate. 

Further, add 1 g. of dry finely powdered aniline hydrochloride to 5 g. of aniline and heat the mixture in a test tube on the water bath at 30°, with 2 g. of dry diazoaminobenzene. Continue heating the frequently stirred mixture for half an hour. Then raise the temperature to 45° and heat again for half an hour. When now a sample no longer evolves nitrogen on heating with hydrochloric acid, dissolve the aniline by adding 24 c.c. of 10 per cent hydrochloric acid (6 c.c. of concentrated acid and 18 c.c. of water). Recrystallise the aminoazobenzene hydrochloride, which remains undissolved, from 100 parts of hot water to which a little hydrochloric acid has been added. In order to obtain the orange-yellow base decompose the salt with sodium carbonate. 

However, the production of the />-phenylenediamine [106-50-3] intermediate is more complex, because it involves the diazotization and coupling of aniline [65-53-3]. Aniline reacts with nitrogen oxides, produced via the oxidation of ammonia, to form 1,3-diphenyltriazene [136-35-6] in the process used by Du Pont (208,209) (see Amines, aromatic-aniline and its derivatives). In the Akzo process a metal nitrite salt and acid in water is used (210). The triazene rearranges in the presence of acid and an excess of aniline to form predominately the p-aminoazobenzene [60-09-3] and a small amount of the ortho isomer, 0-aminoazobenzene [2835-58-7]. The mixture of isomers is catalytically reduced to the respective diamines, and they are then separated from the aniline, which is recycled (208,209). The 0-phenylenedi amine [95-54-5] is used in the manufacture of herbicides (see Amines, aromatic-phenylenediamines). 

Conversion into p-aminoazobenzene. Dissolve 5g (0.025 mol) of finely powdered diazoaminobenzene 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 °C 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 aniline in the form of its soluble acetate. Allow the mixture to stand, with frequent shaking, for 15 minutes filter the aminoazobenzene at the pump, wash with a little water and dry upon filter paper. Recrystallise the crude p-aminoazobenzene (3.5 g, 70% m.p. 120 °C) from 15-20 ml of carbon tetrachloride to obtain the pure compound, m.p. 125 °C. Alternatively, the compound may be recrystallised from dilute ethanol, to which a few drops of concentrated ammonia solution have been added. 

When treated with aniline, diazotized aniline (benzenediazonium chloride) yields, apart from a small quantity of 4-aminoazobenzene (33), diazoaminoben-zene (34) as the main product ... 

Twofotms (l)(3olden-yellow leaflets or prisms from EtOH. M.p. 98 . Decomp. with slight explosion on sudden stroim heating. Sol. EtgO, C Hg. Mod. sol. hot EtOH. Insol. HgO, dil. min. aci<. Hot cone. Hd —> phenol, aniline, and nitrogen. Aniline hydroemoride —> p aminoazobenzene. (2) Yellow prisms. 

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