Diazonium salts from amines

It is synthesized by reaction of the diazonium salt from amine 1 with potassium ethyl xanthate, followed by alkaline hydrolysis to afford thiophenol 2. 

Nitrogen monoxide Diazonium salts from amines... 

Diazonium salts from primary aromatic amines... 

Inclusion of a para acetyl group requires a somewhat different approach to the preparation of these compounds. Reaction of the diazonium salt from p-aminoacetophenone with sulfur dioxide affords the sulfonyl chloride, 203 this is then converted to the sulfonamide, 204, Elaboration via the carbamate with cyclohexyl-amine affords acetohexamide (205). ... 

The chlorine can be disconnected with the alternative polarity via the diazonium salt to amine (19) (guideline 4), The amino group is more powerfully electron-donating than OMe so we can disconnect the NO group. The amino group is itself derived from another nitro group. 

For preparative diazotisations it is important to use a sufficient excess of acid and to keep the temperature down. Two moles of acid are required for each mole of amine, one for salt formation and one for liberating the nitrous acid from the nitrite. As a rule 2-5-3-0 moles are used. The excess is required to prevent condensation of the diazonium salt with unchanged base to diazoamino-compound such condensations take place in a faintly acid medium. The test for unchanged amine, accordingly, consists in buffering the free mineral acid with sodium acetate, and so providing a solution faintly acid with acetic acid, under which conditions the diazoamino-compound is formed. The latter is decomposed by mineral acids into diazonium salt and amine salt, e.g. 

Diazonium salts from primary aromatic amines Ar—NH2 + MONO -------------------------... 

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. 

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). 

By choice of reaction conditions so as to avoid nucleophilic substitution, the diazonium salt from the 3-amine (126) will undergo diazo coupling to form azo dyes (79BRP1550828). 

The foimation of aromatic diazonium salts from aromatic primary amines is one of the oldest synthetic procedures in organic chemistry. Methods based on nitrosation of amine with nitrous acid in aqueous solution are die best known, but diere are variants which are of particular use widi weakly basic amines and for the isolation of diazonium salts fiom nonaqueous media. General reviews include a book by Saunders and AUen and a survey of preparative methods by Schank. There ate also reviews on the diazotization of heteroaromatic primary amines and on the diazotization of weakly basic amines in strongly acidic media. The diazotization process (Scheme 11) goes by way of a primary nitrosamine. 

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). 

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

This linker system is based on the principle that triazenes can be efficiently generated by reactions of diazonium salts with amines. Under basic conditions, these triazenes are stable, but they can be cleaved under mildly acidic conditions to regenerate a diazonium salt and an amine. Based on this system, originally pubhshed by Moore and Tour [151, 152], two different hnkers have been developed. In the so-called T1 variant (Scheme 63), a secondary amine is created on the sohd support and reacted with a diazonium salt to yield the triazene 136. After the synthetic manipulations leading to 137, the triazene is cleaved, resulting in the formation of the initial support and the desired product [153]. Besides the traceless cleavage from the support, the diazonium salt formed as intermediate during the... 

Two common synthetic routes have been used for the synthesis of tetrazoles (Scheme 5). First, the phenyl sulfonyUiydrazones (23) react with the freshly prepared diazonium salts (24) in pyridine under cooled conditions to produce the desired tetrazole products (25) with moderate to good yields [25]. The hydrazones (23) can be synthesized easily from the aliphatic or aromatic aldehydes (21) and the diazonium salts from the corresponding amines with NaNOa under acidic conditions. The second method has been used to prepare the thiophene conjugated tetrazoles (29) which exhibit longer photoactivation wavelength [26-28]. 

Mechanism 25.2 Formation of a Diazonium Salt from a 1 Amine Part[1] Formation of an A/-nitrosamine... 

Another, especially historically important copper-mediated radical aryl-aryl bond forming reaction is the Pschorr reaction (Gomberg-Bachmann reaction), which has been first described in 1896 for the preparation of phenanthrene and its derivatives [85]. Later, in 1924, Gomberg and Bachmann described an intermolecular version of this reaction and prepared several biphenyl derivatives in moderate yield [86]. The reaction is initiated by formation of diazonium salts from aromatic amines, which release nitrogen upon reaction with copper salts. The intermediary formed aryl radial then undergoes the desired coupling reaction and allows the isolation of biaryl compounds. An example of such a reaction is outlined in Scheme 12.23 [87],... 

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 reaction of an aryl diazonium salt with potassium iodide is the standard method for the preparation of aryl iodides The diazonium salt is prepared from a primary aro matic amine m the usual way a solution of potassium iodide is then added and the reac tion mixture is brought to room temperature or heated to accelerate the reaction... 

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... 

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