Diazonium salts from aromatic compounds

Aromatic halogen compounds from diazonium salts (11.12)... 

This reaction was initially reported by Dutt, Whitehead, and Wormall in 1921. It is the preparation of aromatic azide via the basic hydrolysis of aromatic diazoaminosulfinate that can be easily synthesized from aromatic diazonium salt and arylsulfonamide or alkyl-sulfonamide. Therefore, this reaction is known as the Dutt-Wormall reaction. Similarly, azides can be prepared via the cleavage of compounds from diazonium salt with ammonia, hydrazine," hydroxylamine, etc. 

Fast Color Salts. In order to simplify the work of the dyer, diazonium salts, in the form of stable dry powders, were introduced under the name of fast color salts. When dissolved in water they react like ordinary diazo compounds. These diazonium salts, derived from amines, free from solubilizing groups, are prepared by the usual method and are salted out from the solutions as the sulfates, the metallic double salts, or the aromatic sulfonates. The isolated diazonium salt is sold in admixture with anhydrous salts such as sodium sulfate or magnesium sulfate. 

Finally, aryl radicals Ar, which in the presence of hypophosphoric acid (H3P02) are generated from diazonium salts and Cu(I), undergo reduction to the aromatic compounds Ar-H in a radical chain reaction (Figure 5.54). 

Unsymmetrical diaryls may be prepared by treating an aryl diazonium salt solution with sodium hydroxide or sodium acetate in the presence of a liquid aromatic compound. Thus 2-chlorodiphenyl is readily formed from o-chloro phenyl diazonium chloride and sodium hydroxide solution (or sodium acetate solution) in the presence of benzene ... 

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... 

Almost all dyes are quinones or azaquinones of compound 2. The majority are used for thermal transfer processes a recent example is compound 306 (98USP5792587). The second major class are azo dyes, prepared either from aromatic diazonium salts as in compound 307 (95GEP4319296) or from a triazolopyridine 3-diazonium salt as in 308 (81BRP2054630). 

Arylamines are converted by diazotization with nitrous acid into arenediazonium salts, ArN2+ X-. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. Aryl chlorides, bromides, iodides, and nitriles can be prepared from arenediazonium salts, as can arenes and phenols. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines to give brightly colored azo dyes. 

Azo coupling of diazonium salts with aromatic (or pseudoaromatic) hydrocarbons is possible if the coupling agent is highly substituted. For example, azo compounds have been produced from pentamethylbenzene [12], benzpyrene [13], and azulene [1-4]. 

Since A,A -disubstituted hydrazines are readily available from a variety of sources (see Volume I, Chapter 14), their dehydrogenation constitutes a widely applicable route to both aliphatic and aromatic azo compounds. Such oxidative procedures are of particular value in the aliphatic series because so many of the procedures applicable to aromatic compounds, such as the coupling with diazonium salts, have no counterpart. The oxidation reactions permit the formation not only of azoalkanes, but also of a host of azo compounds containing other functional groups, e.g., a-carbonyl azo compounds [83], a-nitrile azo compounds [84], azo derivatives of phosphoric acid [85], phenyl-phosphoric acid derivatives [86],... 

As might be expected, the stability and reactivity of diazonium salts are affected by substituents as well as by the anion. The rate of coupling and the location of the azo bond are influenced by substituents on the coupling reagent. Some primary and secondary aromatic amines derived from benzene initially form A-azo compounds, which rearrange to p-aminoazo compounds in acidic media [8b, c]. Tertiary amines, on the other hand, behave normally. Preparation 2-3, while of a rather complex molecule, illustrates the simple techniques commonly used in coupling in an aqueous system. Note the presumed preferential tendency of coupling to take place predominantly in the para position. 

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. 

Although it is possible to prepare aryl chlorides and aryl bromides by electrophilic aromatic substitution, it is often necessary to prepare these compounds from an aromatic amine. The amine is converted to the corresponding diazonium salt and then treated with copper(I) chloride or copper(I) bromide as appropriate. 

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