Introduction of diazonium groups

The so-called transdiazotizations are mechanistically related to the introduction of diazonio groups using sulfonic acid azides. An aromatic diazonium ion forms a triazene (diazoamino compound) with an aromatic amine the triazene tautomerizes and dissociates at the Na-Np bond of the original diazonium ion. This reaction is important for the synthesis of the 4-aminobiphenyl-4,-diazonium ion, which cannot be obtained by direct (mono-)diazotization of 4,4 -diaminobiphenyl (Allan and... 

As we would expect, introduction of these groups opens the way to the preparation of a series of u/p/ra-substituted naphthalenes from 1-nitronaphthalene via the amine and diazonium Its, and from 1-bromonaphthalene via the Grignard reagent. 

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. 

Some time ago Tedder (1957) recommended a process which he called direct introduction of the diazonium group , because it replaces the steps of nitration, reduction, and diazotization of an aromatic compound by a one-pot operation with three equivalents of a nitrosating reagent in acidic solution. The first step (Scheme 2-35) is a C-nitrosation and the following steps (Scheme 2-36) are the reduction of the nitroso-arene. 

Introduction of Other Nucleophiles Using Diazonium Ion Intermediates. Cyano and azido groups are also readily introduced via diazonium intermediates. The former involves a copper-catalyzed reaction analogous to the Sandmeyer reaction. Reaction of diazonium salts with azide ion gives adducts that smoothly decompose to nitrogen and the aryl azide.56... 

This is, however, a weak electrophile compared with species such as N02 and will normally only attack highly reactive aromatic compounds such as phenols and amines it is thus without effect on the otherwise highly reactive PhOMe. Introduction of electron-withdrawing groups into the o- or p-positions of the diazonium cation enhances its electrophilic character, however, by increasing the positive charge on the diazo group ... 

N-Alkylation of primary aromatic amines increases their nucleophilic character, making them couple much more readily, the introduction of the azo group occurring in the 4-position. Thus, in contrast to aniline, N-methylaniline couples readily and N,N-dimethyl-aniline very readily with simple diazonium salts. Diphenylamine also couples in the 4-position, but less readily than N-methylaniline. 

Theory The nitrous acid, generated on the introduction of sodium nitrite solution into the acidic reaction mixture, reacts with the primary amino group of sulphanilamide quantitatively, resulting into the formation of an unstable nitrite that decomposes ultimately with the formation of a diazonium salt. The diazonium salt thus produced is also unstable, and if the reaction mixture is not maintained between 5-10°C, it shall undergo decomposition thereby forming phenol products which may react further with nitrous acid. The reactions involving the formation of the diazonium salt may be expressed in the following manner ... 

From the above reactions, it is clear that the diazonium salts are very good intermediates for the introduction of -F, -Cl, -Br, -1, -CN, -OH, -NO2 groups into the aromatic ring. 

Direct Introduction of the Diazonium Group Diazoniation or Diazonio-de-hydrogenation... 

Photodecomposition of diazonium salts in hydrochloric acid solution results in the introduction of halogen in place of the diazonium group. For example, irradiation of 4-diazoaminodiphenylamine gives 4-chloro-dipheny lamine.271... 

Azo dyes of this type are classed as donor-acceptor chromogens and basically a red (bathochromic) shift is produced by the introduction of electron withdrawing substituents in the diazonium component and by electron donating substituents in the coupler. An interesting anomaly is the large bathochromic shift produced by am-acetamido group in the coupler (79JCS(P1)1990>. 

Once the acetyl group has been removed by hydrolysis, the molecule is ready for introduction of the iodo substituent by way of a diazonium salt. 

The present, straightforward, two-step synthesis of 5.6-dimethoxyindazole from 3,5-dimethoxyacetophenone illustrates the usefulness of this amination reaction. With standard chemistry the introduction of a hydrazine group into the acetophenone molecule would have required four steps 1) nitration, 2) reduction of the nitro group to the aniline, 3) diazotization and 4) reduction of the diazonium compound to the hydrazine. 

Introduction of the cyano group by the Sandmeyer reaction involves treatment of a diazonium solution with a solution of copper(I) cyanide in aqueous potassium cyanide (Scheme 8.19). 

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