From diazotized amines

BenZimidaZolones. This class of pigments derives its name from 5-aminobenzimidazolone/Pj5 -2J-< 7 which upon reaction with diketene or 2-hydtoxy-3-naphthoyl chloride leads to compounds which can be coupled with a variety of diazotized amines. 

Chemists working with azo dyes use a shorthand designation based on the synthesis by azo coupling. It is characterized by an arrow from the amine used for diazotization (the so-called diazo component) to the coupling component, e. g., for 1.8 sulfanilic acid - 2-naphthol. This designation is especially useful for polyazo dyes (see Zollinger, 1991, p. 109). 

This statement does not mean, however, that the mechanism of diazotization was completely elucidated with that breakthrough. More recently it was possible to test the hypothesis that, in the reaction between the nitrosyl ion and an aromatic amine, a radical cation and the nitric oxide radical (NO ) are first formed by a one-electron transfer from the amine to NO+. Stability considerations imply that such a primary step is feasible, because NO is a stable radical and an aromatic amine will form a radical cation relatively easily, especially if electron-donating substituents are present. As discussed briefly in Section 2.6, Morkovnik et al. (1988) found that the radical cations of 4-dimethylamino- and 4-7V-morpholinoaniline form the corresponding diazonium ions with the nitric oxide radical (Scheme 2-39). 

For reviews of rearrangements arising from diazotization of aliphatic amines, see, in Patai The Chemistry of the Amino Group Wiley NY, 1968, the articles by White, E.H. ... 

Pathway I is the method that first comes to mind but presents somewhat of a problem. It is not possible to synthesize the product in a straightforward two-step sequence by simply coupling two equivalents of diazotized amine with the bifunctional coupling component. This reaction does not afford a definitive product, since the monoazo compound is frequently insoluble enough to precipitate and is thus eliminated from further reaction. 

Arenediazonium tetrafluoroborates 3 arc formed from aromatic amines 1 either by precipitation (shown schematically as a dropping arrow) of the diazonium tetrafluoroborate from an aqueous solution of another soluble diazonium salt 2 or through direct diazotization in aqueous tet-rafluoroboric acid. 

The reactivity to diazo coupling of the 5-position of 2-aminothiophene and the 2-position in 3-aminothiophene complicates the formation of diazonium salts from these amines. However, high yields of azo compounds have been reported from 2-thienyldiazonium chloride prepared from the tin double salt (63AHC(l)l). Aminothiophenes substituted with electron-withdrawing groups are easily diazotized and coupled with dimethylaniline, /3-naphthol, etc. (Section 3.14.2.4). 

The methods used for preparing cyanobenzo[6]thiophenes are merely summarized in the present section they are discussed in more detail elsewhere in this review. Cyanobenzo[6]thiophenes are most conveniently prepared by heating a halobenzo[6]thiophene with cuprous cyanide in a suitable solvent (Section VI, D, 2), or by means of a Sandmeyer reaction of the appropriate diazotized amine (Section VI, F, 4 and 5). Less commonly they are prepared from aldehydes or aldoximes, by methods described in Section VI, L, 1, or from carbox-... 

Derived diazonium compounds, in general, undergo the usual interconversions although yields are often rather low. Reference has already been made (see p. 404) to an unsuccessful attempt to prepare 3-hydroxy-6-methylphenanthridine from the amine.11 1-Amino-phenanthridone gives only impure 1-hydroxyphenanthridone on diazotization in sulfuric acid followed by heating,127 but the method is more satisfactory in the case of 2-amino-iV-methylphenanthri-done.126 Phenanthridones are usually more readily available than the corresponding 6-amino compounds, but as a structural proof phenan-thridone itself has been obtained by the action of nitrous acid on 6-aminophenanthridine.150... 

The derivatives (54 Ar = Ph, />S03HC6H4) have been obtained as crystalline products in good yield by diazotization of the amines (52) (Equation (1)). The intermediate diazonium salts could not be isolated <79ZN(B)275, 80MI 714-01). Using a similar approach, but starting from the amines (53), 2,5-diaryl derivatives have been obtained <93MI 714-01). 

The first 1,2,3-thiadiazole synthesized, 1,2,3-benzothiadiazole, was prepared by diazotiz-ation of o-aminothiophenol with nitrous acid (equation 31) (B-61MI42400), and recently sodium nitrite-acetic acid has been substituted for nitrous acid (B-79MI42400),. Another modification, thermal decomposition of diazonium acetate (34), affords benzothiadiazole in good yield in contrast to the variable yields usually experienced in the diazotization of o-aminothiophenols (equation 32) (78SST(5)43l). Benzothiadiazoles are also available directly from aromatic amines (equation 33) (70JCS(C)2250). Sulfur monochloride reacts with the amine to form a benzothiazothiolium salt which reacts with nitrous acid to yield a chlorinated 1,2,3-benzothiadiazole (35). This process, depending on the aromatic ring substitution, may afford a number of products, and yields are variable. 

Gentle heating of the azides (157 R=N3), obtained from the amines (157 R = NH2) by diazotization followed by treatment with sodium azide, gives high yields of the diaryl... 

The replacement of an amino group by a mercapto group on an aromatic nucleus is effected by treating the diazotized amine with potassium ethyl xanthate and hydrolyzing the resulting aryl ethyl xanthate (Leuckart). Yields of 40-80% are reported for thiophenols containing methyl, halo, and methoxyl groups. Potassium ethyl xanthate is readily prepared from alcoholic potassium hydroxide and carbon disulfide. ... 

The arenediazonium halides are obtained from aromatic amines (on diazotization by one of the standard methods, e.g., using NaN02 and aq HCl near 0°C). The double salts can be obtained as precipitates simply by mixing solutions of the arenediazonium... 

Diazonium compounds, which are formed from aromatic amines with nitrous acid, may react with proteins by electrophilic substitution of the aromatic amino acid residues. Among these, bis-diazotized benzidine (BDB), o-dianisidine, benzidine-(2,2 or 3,3 )-disulphonic acid have been used extensively for protein conjugation (Kennedy et al., 1976a), but they may inactivate the enzyme or the antibody (coupling occurs mainly via the histidyl and tyrosyl residues). 

To probe this, model compounds were prepared and subjected to the reaction. Firstly, formation of the ABE ring system was modeled [14]. Diazotization of the amine 35 and reaction of the resulting diazonium salt afforded the spirocyclic product 36 in an acceptable 57% yield from the amine. This marked the first example where the radical-polar crossover reaction was terminated in an intramolecular manner. Modeling the ABCE tetracycle also worked well in preparing products 40 42. Importantly, the relative stereochemistry of 42, and by implication that of the other tetracycles, was verified by X-ray crystal structure analysis... 

The process most widely used for introducing fluorine into an aromatic nucleus is thermal decomposition of diazonium fluoroborates (Schiemann reaction) lc,1242 1244 these salts are usually very stable, even towards deflagration. They are precipitated (i) on addition of hydrogen tetrafluoroborate or NaBF4 to a diazonium solution obtained as usual from the amine in hydrochloric acid or (ii) on diazotization of the amine in HBF4 solution by aqueous... 

How do the two nitrogens, one from the amine and one from the nitrous acid, become bonded to one another, as they appear in diazonium ions This happens in the first step of diazotization (eq. 11.30), which involves nucleophilic attack of the primary amine on the nitrosonium ion, followed by proton loss. 

Piper, D. J. E., G. J. Barbante, N. Brack, P. J. Pigram, and C. F. Hogan. Highly stable ECL active films formed by the electrografting of a diazotized ruthenium complex generated in situ from the amine. Langmuir 27, 2011 474-480. 

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