Diazonium salts formation from primary amines

Reaction with arenediazonium salts Adding a phe nol to a solution of a diazonium salt formed from a primary aromatic amine leads to formation of an azo compound The reaction is carried out at a pH such that a significant portion of the phenol is pres ent as its phenoxide ion The diazonium ion acts as an electrophile toward the strongly activated ring of the phenoxide ion... 

Amines are characterized by their basicity and, thus, by their ability to dissolve in dilute aqueous acid (Sections 20.3A, 20.3E). Moist pH paper can be used to test for the presence of an amine functional group in an unknown compound. If the compound is an amine, the pH paper shows the presence of a base. The unknown amine can then readily be classified as 1°, 2°, or 3° by IR spectroscopy (see below). Primary, secondary, and tertiary amines can also be distinguished from each other on the basis of the Hinsberg test (Section 20.9A). Primary aromatic amines are often detected through diazonium salt formation and subsequent coupling with 2-naphthol to form a brightly colored azo dye (Section 20.8). 

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... 

Primary aromatic amines differ from primary aliphatic amines in their reaction with nitrous acid. Whereas the latter yield the corresponding alcohols (RNHj — ROH) without formation of intermediate products see Section 111,123, test (i), primary aromatic amines 3neld diazonium salts. Thus aniline gives phcnyldiazonium chloride (sometimes termed benzene-diazonium chloride) CjHbNj- +C1 the exact mode of formation is not known, but a possible route is through the phenjdnitrosoammonium ion tlius ... 

The formation of diazonium salts from aromatic primary amines by reaction with nitrous acid undoubtedly involves the intermediate formation of V-nitroso compounds. The Demjanov and Tiffeneau-Demjanov ring expansions also involve V-nitroso compounds [2]. Some V-nitroso compounds have been used as sources of free radicals and as blowing agents. 

Titanium plays a key role in this process owing to its reducing power in the Ti(III) state, it acts as radical initiator generating Ar- by decomposition of arene-diazonium salts (Equation 14.16) owing to its Lewis acid character in the Ti(IV) state, it promotes the formation of the inline [29] from a generic aldehyde and a primary aromatic amine in the aqueous medium (Equation 14.17) and increases... 

The reaction of aromatic amines with nitrous acid is of considerable importance and the formation of diazonium salts from the primary amines is discussed in detail in Section 8.6. Reaction of nitrous acid with secondary amines does not give diazonium salts, but results instead in A -nitrosation. Tertiary amines such as A, A -dimethylaniline do not N-nitrosate, but undergo electrophilic substitution by the nitrosonium cation (NO ) to give A, A -dimethyl-4-nitrosoaniline (Scheme 8.8). 

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. ... 

Griess diazo reaction. Formation of aromatic diazonium salts from primary aromatic amines and nitrous acid or other nitrosating agents. 

The discovery of stable alkenediazonium salts by Bott initiated some investigations on the reactivity of these compounds, e.g., with the hexachloroantimonate of the 2,2-diethoxyethene-l-diazonium ion (9.100). Saalfrank and Ackermann (1981a, 1981 b) reported that 9.100 reacts with primary amines to give l/f-l,2,3-triazoles. This process might be the result of an initial A-azo-coupling reaction with the amine (characteristic of diazonium salts) with subsequent cyclization of the resulting triazene, or result from attack of the amine at the C()ff)-atom with formation of a diazoalkane that cyclizes (9-45). 

The preparation of heteroarotinoids (9) and (10) Schemes 1.1 and 1.2) [29,31] began with the conversion of the known amines (18) [71] and (19) [72] to the respective fluoroborate diazonium salts (20) and (21), respectively, by standard techniques. Generation of the aromatic free radical was accomplished in acetone in the presence of the stable free radical TEMPO. Cyclization of hetero-substituted aromatic free radicals generally occurs in a regiospecific manner with the formation of an exocyclic primary radical which then couples with a second molar equivalent of TEMPO [73-75]. However, both exo- and endo-cyclic free radicals were generated from salt... 

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