Diazonium salts, coupling

Diazonium salts couple readily with aromatic primary amines, giving diazoamino compounds. If for instance an aqueous solution of aniline sulphate is diazotised with a deficiency of nitrous acid, only part of it is converted into benzenediazonium sulphate and the latter then couples with the unchanged aniline to give diazoaminobenzene. The reaction is carried out at the opti-CeHsNHj.HjSO + HONO = CbHsNjHSO, + zHaO... 

The alternative approach is to pad the fabric with the alkaline naphthol and dry, foUowed by printing directly onto this prepared fabric diazonium salts or stabilized diazonium salts. Coupling is instant and the only further treatment needed is to remove aU the uncoupled naphthol and surface azo pigment in a subsequent washing treatment. Because the choice of colors is limited from one naphthol component, other shades are obtained by using other classes of dye alongside the azoic colors, eg, reactives. This approach is widely used in the production of African prints. 

Both 2- and 3-nitrothiophenes are reduced by tin and hydrochloric acid to the corresponding aminothiophenes. In contrast to anilines, the free bases are very unstable their salts and acyl derivatives, however, are stable. 2-Aminothiophene can be diazotized and the resulting diazonium salt coupled with /3- naphthol. The chemical instability of aminothiophenes compared with aniline is illustrated by the ring opening of 2-amino-3-ethoxycar-bonylthiophenes (157) with ethanolic sodium ethoxide to give cyanothiolenones (158) <75JPR861). 

The reaction is very common in pyrazolone chemistry. Since alkoxypyrazoles and tautomerizable pyrazolones undergo this reaction and 3-pyrazolin-5-ones, like antipyrine, do not, it is assumed that the reaction takes place at C-4 of the OH tautomer. Pyrazolone diazo coupling is an important industrial reaction since the resulting azo derivatives are used as dyestuffs. For instance, tartrazine (Section 4.04.4.1.3) has been prepared this way. 3,5-Pyrazolidinediones react with aryldiazonium salts resulting in the introduction of a 4-arylazo group. As has been described in Section 4.04.2.1.4(v), diazonium salts couple in the 3-position with indazole to give azo compounds. 

Diazonium salts couple to hydroxy-substituted vicinal triazoles (101) with subsequent rearrangement of the hydroxy arylazo compounds (102) to the carbamoyl tetrazole (104).170 An open-chain intermediate (103) has been proposed.169 This rearrangement is similar to that of the benzoyl... 

Benzidine yellow is an example of a large class of organic pigments that contain an azo linkage, -N=N-. Its synthesis relies very heavily on diazonium salt coupling reactions and the benzidine rearrangement. Although benzidine is banned in the U.S. because of suspected... 

Carbazole-1- and carbazole-3-amino groups have been diazo-and the diazonium salts coupled with 1,3-dike-tones and ethyl acetoacetate, used in Sandmeyer reactions, reduced to the hydrazines and made to effect intramolecular arylation of a 9-aryl group, such as in the transformation of 215 (R = Me or C02Me) into 216 (R = Me or C02Me). It is worth repeating the earlier observation... 

A number of observations have been made in which two molecules of a diazonium salt couple with each other with loss of one molecule of nitrogen. In this reaction the azo bridge forms by displacement of one of the diazonium salt groupings by the entering group. 

The free bases are much less stable than aniline, particularly 2-amino-pyrroles and -furans which are very easily oxidized or hydrolyzed. 2-Aminofurans substituted with electron-withdrawing groups (e.g. N02) are known and 3-amino-2-methylfuran is a relatively stable amine which can be acylated and diazotized. 2-Aminothiophene can be diazotized and the resulting diazonium salt coupled with (3-naphthol. 2,3-Diaminothiophene has been prepared and isolated as the hydrobromide. The free base is not stable (85JCR(S)296). 

Thiadiazoles amination, 6, 562 diazonium salts coupling reactions, 6, 484 electrophilic attack at carbon, 5, 56... 

Reaction of Diazonium Salts with Quinones and with Phenols. Aryl-diazonium salts couple with quinones in the presence of sodium acetate to... 

Although attempts to make pyrrole diazonium salts couple inter-molecularly have been unsuccessful, 3-diazo-2,4,5-triphenylpyrrole (21) on prolonged heating in dilute sulfuric acid undergoes internal coupling (21- -41).21 That coupling occurred with the phenyl group in the 4-position rather than the 2-position is shown by the formation of the diketone (42) on oxidation with nitric acid. 

The amino group of 4-amino-3-pyrazolin-5-ones can be diazotized easily and the resulting diazonium salt couples with the usual reagents. Other diazonium salts couple with 4-amino-3-pyrazolin-5-ones at the amino group. Mercuric halides replace the amino hydrogen in 2,3-dimethyl-l-phenyl-4-sulfamino-3-pyrazolin-5-one.543 The 4-amino groups react normally with isothiocyanates,49 epoxides,1261 ureas1367 and nitrosamines.527... 

When the diazotization is conducted in the presence of N-(l-naphthyl) ethy-lenediamine, the reactive diazonium salt couples with the amine to form an intenselycolored, reddish purple azo compound (Eq. 4.9). 

H Chemical shifts of azobenzene-like compounds,8-26 ortho-, ortho -dihydroxyazopyrazole27 and diazonium salts coupling products with guaiacol,28 5-aminopyrazole,29 2-phenyl-5-oxazolone,30 3-(4-methoxyphenyl)-1 -oxo- 1H,5H-pyrido[l,2-a]benzimidazole,31 2 - ortho, meta, paru-aminophenyl)oxazolo-... 

Table 9 gives the 13C chemical shifts of the compounds77 (3—40) listed in Table 5. Depending on the nature and orientation of the substituents in the dyes, different conformers, resultant from inner rotation around the C-N bonds, could be identified. The 13C chemical shifts of azobenzene-like compounds and diazonium salts coupling products with heterocycles are reported in Refs. 9, 18, 25, 26, 36, 39, 48, 78-87. The 13C chemical shifts of dyes derived from 3-methyl-l-phenylpyrazol-5-one (of type 78 Table 10),88 pyridone (81),39 and acetoacetanilide (82)65 existing completely in hydrazone forms were assigned.

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