Diazonium salt coupling reactions

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... 

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

Section 2 of this review covers the literature dealing with NMR spectra of azo dyes measured in solution since the publication of last review in 1993 and focuses on azo compounds. Hydrazo compounds have been included either when prepared by diazonium salt coupling reactions or when they are important for azo-hydrazone tautomerism description. The C and N CP/MAS NMR spectra are discussed in Section 3. Azo-hydrazone tautomerism, a property that is indivisibly linked to azo dyes, is the topic of Section 4. NMR spectra of metal complexes of azo dyes are reviewed in Section 5. 

NH2) = —276.4 ppm), whereas in the major tautomer it is considerably higher (6( NH2) = —228.9) and closer to 6( NH—) of the imino group. 4-Dimethylaminopent-3-ene-2-one undergo a subsequent diazonium salt coupling reaction to give compound 50. ... 

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... 

Aminothiazole (58, 235, 391) and 2-amino-4-alkylthiazoles (391. 399) couple with diazonium salts. This reaction takes place in the 5-position and is possible even when bulky substituents occupy the 4-position. as exemplified by the reaction of 191 (Scheme 121) (400. 401). Me... 

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. 

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. 

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

Use diazonium salts in reactions involving arylamines, including diazo coupling reactions. 

Salts of primary aromatic amines react with nitrous acid to produce diazonium salts. The reaction is usually performed by adding a cold solution of sodium nitrite to a cold solution of the arylamine in aqueous mineral acid. The end point of the reaction is conveniently determined by the detection of excess nitrous acid with potassium iodide-starch paper. Sulfamic acid has long been used both in industry and in the laboratory to remove excess nitrous acid. It has been found to react with the more active diazo compounds. In most cases, high temperatures are avoided to prevent the formation of phenols and the decomposition of the unstable nitrous acid. An excess of mineral acid is necessary to prevent coupling between the diazonium salt and unreacted amine (cf. method 494). If the amine salt is somewhat insoluble, a fine crystalline form, which is produced by rapid crystallization from a warm aqueous solution, may be employed. ... 

An attempt to construct a thiadiazine I, I-dioxide ring through diazonium salt coupling gave instead a nitro n-free ring by a Pschorr reaction. 

Perhaps the most characteristic reaction of dihydrodiazepinium salts is their electrophilic substitution at position 6. Thus they are readily deuteriated,20 26 4142 halogenated,9 15 26 35 and nitrated,28 43 44 and couple with diazonium salts.45 Reaction occurs under conditions similar to those... 

A related process that involves diazonium salts is the Pschorr reaction, hich also couples aryl diazo-nium compounds to other aromatic rings. This diazonium salt coupling can he done under acidic conditions, but addition of copper powder usually promotes the radical process. Aryl amines generate aryl diazonium salts upon treatment with nitrous acid.l An example is the reaction of 233 to give an aryl diazonium salt, which cyclized in the presence of copper to give thaliporphine (234) in 43% yield. Kupchan called this transformation an improved Pschorr reaction. 68... 

First attempts to prepare poly(phenylene) date back to 1842 [78]. Riese describes a process in which poly(phenylene) ( =13) is synthesized from 1,4-dibromobenzene and sodium. Further methods are the Ullmann reaction, thermal decomposition of diazonium salts, coupling of phenylene dihalogenide - Grignard compounds. 

The most important reaction of the diazonium salts is the condensation with phenols or aromatic amines to form the intensely coloured azo compounds. The phenol or amine is called the secondary component, and the process of coupling with a diazonium salt is the basis of manufacture of all the azo dyestuffs. The entering azo group goes into the p-position of the benzene ring if this is free, otherwise it takes up the o-position, e.g. diazotized aniline coupled with phenol gives benzeneazophenol. When only half a molecular proportion of nitrous acid is used in the diazotization of an aromatic amine a diazo-amino compound is formed. 

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... 

An interesting coupling reaction with the diazonium salt derived from anthranilic acid leads to an excellent method for the preparation of dlphenic acid. The reaction occurs with cuprous salts in ammoniacal solution ... 

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