Diazonium salts using

Substitution of an aromatic amino group by fluorine via a diazonium salt using fluoroborates... 

The mass spectrometry of diazo compounds was reviewed by Zeller (1983) and by Lebedev (1991). It is difficult to record mass spectra of diazonium salts using conventional techniques. With the water thermospray method, however, Schmelzeisen-Redeker et al. (1985) observed the diazonium ion and various fragments such as [Ar+ - N2 + 2H]+ and [Ar + N2 + H20]+. Ambroz et al. (1988) applied the fast atom bombardment (FAB) technique using a 3-nitrobenzylalcohol matrix. Peaks for ArNJ, Ar+, and [M + ArN2]+ and further peaks due to solvated ions were found. 

There are apparent exceptions to the rule that aromatic compounds are azo coupling components only if they contain a hydroxy or an amino group. A long time ago Meyer and Tochtermann (1921) demonstrated that the 2,4,6-trinitrobenzenedi-azonium salt couples with mesitylene, isodurene (1,2,3,5-tetramethylbenzene), and pentamethylbenzene (see also Smith and Paden, 1934). That result was surprising at the time, but today it is, of course, understandable the diazonium salt used is pro-... 

More recently, Bagal and coworkers (Luchkevich et al., 1991) obtained similar results in a kinetic investigation of the coupling reactions of some substituted benzenediazonium ions with 1,4-naphtholsulfonic acid, and with 1,3,6-, 2,6,8-, and 2,3,6-naphtholdisulfonic acids. The kinetic results are consistent with the transient formation of an intermediate associative product. The maximum concentration of this product reaches up to 94% of the diazonium salt used in the case of the reaction of the 4-nitrobenzenediazonium ion with 1,4-naphtholsulfonic acid (pH 2-4, exact value not given). The authors assume that this intermediate is present in a side equilibrium, i. e., the mechanism of Scheme 12-77 mentioned above rather than that of Scheme 12-76, and that the intermediate is the O-azo ether. 

Amino- and 7-aminothiocoumarin have been thoroughly explored as useful precursors to a wide variety of thiocoumarins. Thus, substituents such as Cl, Br, I, SCN, CN, OH, and OMe have been introduced by way of the Sandmeyer reaction. 6-Aminothiocoumarin is brominated in the 5-posi-tion, whereby 5-bromo- or 5,6-dibromothiocoumarin may be made by way of the corresponding diazonium salt, using hypophosphorous acid or cuprous bromide, respectively. Alternatively, 6-acetylaminothiocoumarin may be nitrated in the 5-position and thus 5-nitro-, 5-amino-, 5,6-diamino-, or 6-chloro-5-nitrothiocoumarins can be prepared by classical syntheses. These derivatives are useful intermediates for the synthesis of further fused thiocoumarins (e.g., 23, 24 and 25 ). 

Cyclization of diazonium salts using iodide ion had been well developed by Beckwith s group, but the iodide corresponding to 50 is a secondary neopentyl iodide, which would be impossible to convert by S 2 chemistry into an alcohol. Our efforts to convert similar iodides to acetate esters with silver acetate by S l have also not met with success. Even if such conversions were possible, they would still be much less direct than with the new radical-polar crossover methodology. 

Reducer added Times for evident polymerization, min., diazonium salt used ... 

Oiazonium Salt Formation. The aromatic amino group of aminophenols can be converted to the diazonium salt using sodium nitrite in aqueous acid, although difficidties may be encoimtered when the aminophenol is of low solubiUty or easily oxidized Crystalline diazonium salts have been isolated using the hydrochloride or sidfate of the appropriate aminophenol under anhydrous conditions. Such diazo derivatives find extensive use in the dye industry (27,28). 

Now that the amino group is fixed we can displace it via a diazonium salt using any chosen nucleophile—copper cyanide for example ... 

Scheme 4.21 Diazonium salts used for azo couplings of 2-naphthol and cresol novolaks [43].

Variations and improvements on the Demanjov and Tiffeneau-Demjanov reaction have been limited. Variations have come in different methods to generate diazonium salts using various acids containing non-nucleophilic counter ions. The use of weaker acids for the Demanjov rearrangement led to diminished amounts of olefmic by-products. Understanding how facile the reaction was at lower temperature also provided higher yield and fewer byproducts. 

Roglans and coworkers [53,54] also studied the Heck reaction of arene diazonium salts using a palladium(O) complexes of 15-membered macrocyclic triolefines. 

C]malonate is sufficient to couple with aryl diazonium salts using aqueous sodium acetate as a base. In the presence of a tautomerizable hydrogen, the azo compound initially formed (e.g., 388) isomerizes to the corresponding hydrazone (e.g., 389). Derivatives of this structural class have been used for the preparation of binuclear heteroaromatic systems. Saponification of the ester groups of hydrazone 389. for example, generated... 

The Chemische Fabrick L. van der Grinten, of Venlo devised an alternative system, known as a one-component system, that uses paper coated with a stabilized diazonium salt, but no phenol. Coupling is achieved after exposure by developing the paper in an alkaline solution of a phenol. The original diazonium salt used was 4-diethylaminobenzenediazonium associated with a complex anion. Choice of the phenolic component allowed modification of the color of the final image. 

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