Nucleophiles reaction with diazonium

The preparation of 5-azothiazoles uses the nucleophilic character of C-5 carbon in reaction with the appropriate diazonium salt (402, 586). These 5-azothia2oles form 1 1 complexes with Ag (587). 2-Amino-4-methyl-5-arylazothiazoles give reduction waves involving two-electron transfer the Ej/ values correlate to the angle between the thiazole and phenyl rings (588). 

In the reactions of nucleophiles with diazonium ions the rate-determined product is, in many cases, a (Z)-azo compound, in spite of the fact that the (is)-isomers are... 

As far as we are aware, the azo coupling of an ethyne derivative was only investigated over half a century ago Ainley and (Sir Robert) Robinson (1937) investigated the reaction of phenylethynes (phenylacetylenes) with diazonium ions (Scheme 12-59). Unsubstituted phenylethyne did not give identifiable products with the 4-nitrobenzenediazonium ion, but with the more nucleophilic 4-methoxyphenyl-ethyne an azo compound (12.119) was formed. On reaction with water it gives an arylhydrazone of an a-ketoaldehyde (12.120). 

Primary aromatic amines (e.g., aniline) and secondary aliphatic-aromatic amines (e. g., 7V-methylaniline) usually form triazenes in coupling reactions with benzenedi-azonium salts. If the nucleophilicity of the aryl residue is increased by addition of substituents or fused rings, as in 3-methylaniline and 1- and 2-naphthylamine, aminoazo formation takes place (C-coupling). However, the possibility has also been noted that in aminoazo formation the initial attack of the diazonium ion may still be at the amine N-atom, but the aN-complex might rearrange too rapidly to allow its identification (Beranek and Vecera, 1970). 

The diazonium group can be replaced by a number of groups. Some of these are nucleophilic substitutions, with SnI mechanisms (p. 853), but others are free-radical reactions and are treated in Chapter 14. The solvent in all these reactions is usually... 

In these reactions, diazonium salts are cleaved to aryl radicals, in most cases with the assistance of copper salts. Reactions 14-17 and 14-18 may also be regarded as belonging to this category with respect to the attacking compound. For nucleophilic substitutions of diazonium salts, see 13-17-13-20. 

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... 

Accordingly, many reactions can be performed on the sidewalls of the CNTs, such as halogenation, hydrogenation, radical, electrophilic and nucleophilic additions, and so on [25, 37, 39, 42-44]. Exhaustively explored examples are the nitrene cycloaddition, the 1,3-dipolar cycloaddition reaction (with azomethinylides), radical additions using diazonium salts or radical addition of aromatic/phenyl primary amines. The aryl diazonium reduction can be performed by electrochemical means by forming a phenyl radical (by the extrusion of N2) that couples to a double bond [44]. Similarly, electrochemical oxidation of aromatic or aliphatic primary amines yields an amine radical that can be added to the double bond on the carbon surface. The direct covalent attachment of functional moieties to the sidewalls strongly enhances the solubility of the nanotubes in solvents and can also be tailored for different... 

Sandmeyer-type reactions are a useful route to polynitroarylenes with unusual substitution patterns. In these reactions an arylamine is treated with a source of nitrous acid to form an intermediate diazonium salt which is readily displaced on reaction with a suitable nucleophile. Many substituents can be incorporated into the aromatic ring via this method, including the nitro group. 

Amino derivatives of 1,2,3- and 1,2,4-triazoles are useful precursors to the corresponding nitro-substituted triazoles. 3-Amino-1,2,4-triazole (98) undergoes diazotization on reaction with nitrous acid the resulting diazonium salt (110) can react with a range of nucleophiles, including an aqueous solution of sodium nitrite which yields 3-nitro-1,2,4-triazole (111). Diazotization of 3,5-diamino-l,2,4-triazole (112), followed by heating with an aqueous solution of sodium nitrite, yields 3,5-dinitro-1,2,4-triazole (113). ... 

This chapter is concerned with reactions that introduce or replace substituent groups on aromatic rings. The most important group of reactions is electrophilic aromatic substitution. The mechanism of electrophile aromatic substitution has been studied in great detail, and much information is available about structure-reactivity relationships. There are also important reactions which occur by nucleophilic substitution, including reactions of diazonium ion intermediates and metal-catalyzed substitution. The mechanistic aspects of these reactions were discussed in Chapter 10 of Part A. In this chapter, the synthetic aspects of aromatic substitution will be emphasized. 

Chloro- and bromo-l,3,4-thiadiazoles are usually prepared by nucleophilic processes, e.g., Sandmeyer reactions of diazonium salts [56CB1534 68AHC(9)165 86CHE1148], and reactions of thiadiazolinones with phosphorus halides [68AHC(9)165]. The halogeno derivatives are important... 

The mechanism by which a nucleophile displaces the diazonium group depends on the nucleophile. While some displacements involve phenyl cations, others involve radicals. Nucleophiles, e.g. CN , Cl and Br , replace the diazonium group if the appropriate cuprous salt is added to the solution containing the arene diazonium salt. The reaction of an arene diazonium salt with cuprous salt is known as a Sandmeyer reaction. 

The diazonium group can be replaced by a number of groups.222 Some of these are nucleophilic substitutions, with SnI mechanisms (p. 644), but others are free-radical reactions and are treated in Chapter 14. The solvent in all these reactions is usually water. With other solvents it has beeen shown that the SnI mechanism is favored by solvents of low nucleo-philicity, while those of high nucleophilicity favor free-radical mechanisms.222 (For formation of diazonium ions, see 2-49.) The N2 group can be replaced by Cl, Br. and CN, by a nucleophilic mechanism (see OS IV, 182). but the Sandmeyer reaction is much more useful (4-25 and 4-28). As mentioned on p. 651 it must be kept in mind that the N2 group can activate the removal of another group on the ring. 

Aromatic Diazonium Ions. In contrast to alkyldiazonium ions, aryldiazonium ions are well-studied.469 77 They were known as early as 1894. They are isolable as ionic salts with a variety of counterions such as BIT, PF6, SbCl6, SbF6, AsF6-, and C104. They undergo a variety of nucleophilic reactions and an excellent review is available on the subject.478... 

Benzotriazoles, for example, are accessible from o-aminoaryl-substituted triazenes after a two-step reaction sequence a nucleophilic displacement followed by cleavage/heterocyclization.35 The nucleophilic halide displacement of activated haloarenes is an indispensable tool for the synthesis of highly substituted arenes. Fluoronitroarenes in particular have served as excellent precursors in this transformation. Thus, it was appealing to combine this SNAr reaction with the flexibility of diazonium chemistry. In this case, an immobilized fluoronitrophenyl triazene would be the equivalent of the Sanger reagent. 

Primary amines react with nitrous acid to yield a diazonium salt, which is highly unstable and degradates into a carbocation that is capable of reaction with any nucleophile in solution. Therefore, reacting primary amines with nitrous acid leads to a mixture of alcohol, alkenes, and alkyl halides. 

The diazo group can be replaced by a number of different nucleophiles. Although several different mechanisms may operate, it is easiest to remember the reactions if you consider them all to be simple nucleophilic substitutions, even though most are not. The following equations provide examples of the various substitutions that can be accomplished with diazonium ions. 

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