Primary aromatic amines diazotization

Diaznnium salts are almost always prepared by diazotizing primary aromatic amines. Primary arylamines can be synthesized through reduction of nitro compounds that are readily available through direct nitration reactions. 

Diazotized -nitroaniline can be substituted by other diazotized primary aromatic amines. ... 

Azo colors comprise that largest group of certified colorants. They are characterized by the presence of one or more azo bonds (—N=N—) and are synthesized by the coupling of a diazotized primary aromatic amine to a coupling component, usually a naphthol. Certifiable azo colors can be subdivided into four groups insoluble unsulfonated pigments, soluble unsulfonated dyes, insoluble sulfonated pigments, and soluble sulfo-nated dyes. 

Azo-dye formation. Most phenols and keto-enolic compounds couple with diazotized primary aromatic amines to give highly coloured azo-dyes (see pages 66 et seq). 

Synthesis. Almost without exception, azo dyes ate made by diazotization of a primary aromatic amine followed by coupling of the resultant diazonium salt with an electron-rich nucleophile. The diazotization reaction is carried out by treating the primary aromatic amine with nitrous acid, normally generated in situ with hydrochloric acid and sodium nitrite. The nitrous acid nitrosates the amine to generate the N-nitroso compound, which tautomerizes to the diazo hydroxide. 

Primary aromatic amines are first diazotized and then coupled to yield azo dyestuffs [4],... 

Note Note that the diazotization of primary aromatic amines can also be achieved by placing the chromatogram for 3 — 5 min in a twin-trough chamber containing nitrous fumes (fume cupboard ). The fumes are produced in the empty trough of the chamber by addition of 25% hydrochloric acid to a 20% sodium nitrite solution [2, 4], iV-(l-Naphthyl)ethylenediamine can be replaced in the reagent by a- or -naphthol [10, 14], but this reduces the sensitivity of detection [2]. Spray solutions Ila and lib can also be used as dipping solutions. 

Griess (1864a) had already observed that the diazo compounds obtained from primary aromatic amines in acid solution are converted by alkalis into salts of alkalis. The reaction is reversible. The compounds which Hantzsch (1894) termed sjw-diazotates exhibit apparently the same reactions as the diazonium ions into which they are instantaneously transformed by excess of acid. Clearly the reaction depends on an acid-base equilibrium. 

This type of scheme for the nitrosation of primary aromatic amines was first used by Ridd in 1959. The comparison of the present scheme with that from 1959 demonstrates how much more diversified the knowledge on diazotization mechanisms has become in three decades. 

Primary aromatic amines are first diazotized by the action of sodium nitrite in acid solution and then coupled, for instance, with 1-naphthol to form azo dyes (cC Bratton-Marshall reagent, Vol. 1 a). ... 

Azo pigments are typically formed by a reaction sequence of diazotization and coupling, involving a primary aromatic amine, which is referred to as a diazo component, and a nucleophilic aromatic or aliphatic compound with active methylene groups as a coupling component [1-3]. 

Diazotization is the reaction of a primary aromatic amine with a nitrosating agent, such as sodium nitrite or, to a lesser extent, with nitrosylsulfuric acid N0S04H, nitrous gases, or organic nitrites in an aqueous acidic solution at a temperature between 0 and 5°C, converting the amine to its diazonium salt ... 

Contrary to earlier assumptions, the aryl ammonium ion is not able to undergo diazotization since the crucial step in the diazotization mechanism is the electrophilic nitrosation of the free amino group in the free-base primary aromatic amine 12 ... 

Tertiary aromatic amines may be nitrosated directly with nitrous acid, whereas primary aromatic amines normally are diazotized under these conditions. Some phenols may also be nitrosated under conditions similar to those used for the nitrosation of tertiary amines. 

The primary aromatic amines which will be preferentially nitrosated rather than diazotized are those which do not bear strongly electron-withdrawing substituents and are capable of coupling with diazonium salts to give azo dyes. 

Almost without exception, azo dyes are made by diazotization of a primary aromatic amine followed by coupling of the resultant diazonium salt with an electron-rich nucleophile. 

Primary aromatic amines react with nitrous acid to give aryldiazonium ions, ArN2+, which are useful intermediates in synthesis of aromatic compounds. The process by which they are formed is called diazotization. The nitrogen in these ions can readily be replaced by various nucleophiles (OH, Cl, Br, I, CN). Diazonium ions couple with reactive aromatics, such as amines or phenols, to form azo compounds, which are useful as dyes. 

Write an equation for the diazotization of a given primary aromatic amine. 

Chloro-2-nitroaniline. Primary aromatic amines should be protected by acetylation before nitration to avoid the possibility of accidental diazotization.19 Crotonaldehyde. Ignites in concentrated HN03.2... 

It is evident that the success of the deamination process is a function of the completeness of diazotization as well as of the reduction. Fortunately, practically any primary aromatic amine is susceptible of diazotization, usually in yields approaching the theoretical. The conditions for this reaction are comparatively standard and are fully described in monographs on the diazo compounds.1... 

Scheller 17 modified the Bart reaction to such an extent that his method is often referred to as the Scheller reaction. Primary aromatic amines, dissolved in methanol or glacial acetic acid, are diazotized in the presence of arsenic trichloride and a trace of cuprous chloride. Removal of the solvent followed by treatment with water and sodium hydrosulfite gives the expected arsonic acids. 

Diazotization. The conversion of a primary aromatic amine to a diazonium compound is... 

All classical azo reds contain at least one azo group, by definition, and are all produced by a similar reaction sequence involving the chemical reaction termed dia-zotization followed by coupling. Diazotization involves reacting a primary aromatic amine with nitrous acid to yield a diazonium salt, which is then immediately coupled to the other half of the molecule to yield the colored pigment as a bright red precipitate. 

As described in Chapter 8, the indirect replacement of an amino group by a halogen via diazotization of a primary aromatic amine is a valuable route to aryl halides. The chemistry of these processes covering the introduction of all the main halogens can be found in that chapter. 

Azoic dyes. Azo dyes contain at least one azo group (—N=N—) attached to one or often two aromatic rings. They are produced in textile fibers (usually cotton, rayon, and polyester), by diazotization of a primary aromatic amine followed by coupling of the resulting diazonium salt with an electron-rich nucleophile (azo coupling). A variety of hues can be obtained... 

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