Aromatic diazonium salts, reaction with

Aromatic diazonium salts react with sulphur dioxide, either in the liquid state or mixed with an organic solvent, such as acetic acid, in the presence of copper(II) chloride to give 50-90% yields of sulphonyl halides205,527-529 (equation 138). Nitrogen is evolved during the reaction and higher yields are usually obtained in the presence of a solvent. 

The cycloaddition between furan and maleic anhydride was the first uncatalyzed aqueous Diels-Alder reaction reported in the literature and was studied by Diels and Alder themselves [11]. This cycloaddition was successfully revised by Woodward and Baer [12] and some years later by De Koning and coworkers [13]. The aqueous medium was also used in the cycloaddition of aromatic diazonium salts with methylsubstituted 1,3-butadienes [14]. 

Diazonium salts react with various nucleophiles in water (Eq. 11.62).106 In acidic aqueous solution, p-pheny I e ncbis di azo ni um ion reacts with alcohols more rapidly than it does with water.107 In the presence of nucelophiles such as halides, the substitution products are obtained. Furthermore, diazonium salts of aromatic compounds are excellent substrates for palladium-catalyzed coupling reactions such as the Heck-type reactions in water. 

Displacement of nitrogen from diazonium salts derived from 4- or 5-aminotriazoles can be achieved in the same manner as for other aromatic diazonium salts for example, diazotization of 4-amino-triazole-5-carboxamide and reaction with iodine and potassium iodide gives the 4-iodo derivative. ... 

The reaction of phenacyltriphenylarsonium bromides (333) with aromatic diazonium salts in methanol containing sodium acetate provides a simple method for synthesizing 3,6-diaroyl-l,4-dihydro-l,2,4,5-tetrazines (334) in good yield (78JOM(155)293). The reaction has been postulated to proceed via the nitrilimine intermediate (335), whose formation can be explained by the sequence shown in Scheme 19. 

Triazenes have been prepared by the treatment of resin-bound aromatic diazonium salts with secondary amines (Figure 3.27). Regeneration of the amine can be effected by mild acidolysis (Entry 1, Table 3.23). Triazenes have been shown to be stable towards bases such as TBAF, potassium hydroxide, or potassium tert-butoxide [454], and under the conditions of the Heck reaction [455]. Primary amines cannot be linked to supports as triazenes because treatment of triazenes such as R-HN-N=N-Ar-Pol with acid leads to the release of aliphatic diazonium salts into solution [373]. Triazenes derived from primary amines can, however, be used for the preparation of amides and ureas (see Section 3.3.4),... 

Support-bound triazenes, which can be prepared from resin-bound secondary aliphatic amines and aromatic diazonium salts [455], undergo cleavage upon treatment with acids, leading to regeneration of the aromatic diazonium salts. In cross-linked polystyrene, these decompose to yield nitrogen and, preferentially, radical-derived products. If the acidolysis of polystyrene-bound triazenes is conducted in the presence of hydrogen-atom donors (e.g. THF), unsubstituted arenes can be obtained (Entries 8 and 9, Table 3.47). In the presence of alkenes or alkynes and Pd(OAc)2, the initially formed diazonium salts undergo Heck reaction to yield vinylated or alkynylated arenes (Entry 10, Table 3.47). Similarly, unsubstituted arenes can be obtained by oxida-... 

The reaction of phenacyl or substituted-phenacyl triphenylarsonium bromide with aromatic diazonium salts gave l,4-dihydro-l,2,4,5-tetrazine (60) (6). 

The triazene linker can be used for the immobilization of aromatic diazonium salts, and therefore for aromatic amines, but not for aliphatic amines due to the instability of their diazonium salts. Cleavage of the linker can be achieved under mild acidic conditions to yield the benzylamine resin and the corresponding diazonium salt [136,145,146]. The main difference between the preparation of triazenes in solution and triazenes on solid support is the respective amine, namely bisben-zylamine and polymer-supported benzylamine 114. In solution, it was used in excess to quench unstable diazonium salts and force the reaction to completion. In the solid-phase approach it was immobilized and cannot be used in excess with respect to low loadings. A simple three-step procedure (Scheme 36) starting from benzylamine resin 114 via carboxylate 115 led to the successful preparation of ester resins 116 in essentially higher loadings. Treatment of resin 114 with 4-carboxy-benzene diazonium tetrafluoroborate yielded benzoic acid resin 115. 

Primary aromatic amines on reaction with nitrous acid in the presence of hydrochloric acid (or other mineral acid) at about 0 °C yield diazonium salts as discrete intermediates. The diazonium salts similarly derived from aliphatic primary amines decompose readily even at this temperature to yield the corresponding alcohol (and other products) with the evolution of nitrogen. 

Diazonium salts of aromatic amines are very useful as intermediates to other compounds. Because aromatic diazonium salts are only stable at very low temperatures (zero degrees and below), warming these salts initiates decomposition into highly reactive cations. These cations can react with any anion present in solution to form a variety of compounds. Figure 8-2 illustrates the diversity of the reactions. 

Write the equations for the reaction of an aromatic diazonium salt with aqueous base HX + Cu2X2 (X = Cl, Br) KCN + Cu2(CN)2 HBF4 and H3P02. 

The 4-aminopyridine derivative 92, prepared from the reaction of ethyl benzoylacetate and malononitrile dimer 91, undergoes the coupling reaction with aromatic diazonium salts to afford azo derivatives such as 93. Under refluxing conditions in ethanolic sodium hydroxide, these azo compounds cyclize to pyrido[3,2-f]pyridazines and pyrido[3,2-r]-pyridazino[2, 3 - ]quinazolines (Scheme 15) <2005AP329>. 

To conduct the substitution reactions of Figure 5.56, one neutralizes an acidic solution of the aromatic diazonium salt with diethylamine. This forms the diazoamino compound B (called a triazene ). It is isolated and subjected to the substitution reactions in an organic solvent. In each case, at first a leaving group is generated from the NIT, moiety of the dia-... 

In 1975 Carlson, Sheppard and Webster showed that the products of an old, known reaction between dienes and aromatic diazonium salts are not coupling products, but rather, they are dihydropyridazines. A detailed investigation of this reaction, in particular with electron-rich dienes, revealed the cycloaddition is concerted, and 3,6-dihydropyridazines 19 are formed first. They are transformed further into either 1,6-dihydropyri-dazines 20 or pyridazinium ions (84TL57). 

A diazonium salt reacts with copper(I) chloride or copper(I) bromide to form an aryl chloride or aryl bromide, respectively. This is called the Sandmeyer reaction. It provides an alternative to direct chlorination and bromination of an aromatic ring using CI2 or Br2 and a Lewis acid catalyst. 

Oxygen reacts readily with aromatic sulfides [341], AT-methionyl peptides [342], 1,3-dithianes [343], aziridines [344], and phosphorus [345] compounds after oxidation. On the other hand, aryl radicals are involved in the ET reaction of trivalent phosphorus compounds with aromatic diazonium salts [346]. 

The CH2 group of co-imidazol-l-yl)acetophenone 1004 is sufficiently activated by the carbonyl and the imidazole group that it readily reacts with aldehydes, aromatic diazonium salts (to form diazo compounds) and acrylonitrile. The reaction of 1004 with phenyl isothiocyanate in the presenceof KOH results in the formation of adduct 1005 that is not isolated but further condensed with phenacyl bromide to afford thienylimidazole 1006 in 87% yield (Scheme 241) <2003SC153>. In the presence of a 2-sulfanyl group 1007, the enolate of ot-imidazolyl acetophenone 1008 no longer reacts with aldehydes or even alkyl halides except for Mel 1009 <200282691 >. 

Incidentally, 34 contributes more to the hybrid than 35, as shown by bond-distance measurements. In benzenediazonium chloride, the C—N distance is 1.42 A, and the N—N distance 1.08 A, which values fit more closely to a single and a triple bond than to two double bonds (see Table 1.5). Even aromatic diazonium salts are stable only at low temperatures, usually only < 5°C, although more stable ones, such as the diazonium salt obtained from sulfanilic acid, are stable up to 10 or 15°C. Diazonium salts are usually prepared in aqueous solution and used without iso-lation, although it is possible to prepare solid diazonium salts if desired (see 13-23). The stability of aryl diazonium salts can be increased by crown ether complexion. For aromatic amines, the reaction is very general. Halogen, nitro, alkyl, aldehyde, sulfonic acid, and so on, groups do not interfere. Since aliphatic amines do not react with... 

Aromatic diazonium salts, obtained in titrations with sodium nitrite, can be used in azo-coupling reactions. ... 

Primary aromatic amines react with nitrous acid to yield diazonium salts this is one of the most important reactions in organic chemistry. Following sections are devoted to the preparation and properties of aromatic diazonium salts. 

Under the proper conditions, diazonium salts react with certain aromatic compounds to yield products of the general formula Ar—N==N—Ar, called azo compounds. In this reaction, known as coupling, the nitrogen of the diazonium group is retained in the product, in contrast to the replacement reactions we have studied up to this point, in which nitrogen is lost. 

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