Diazonium sulfonate, formation

In some cases the use of nitrosylsulfuric acid may be avoided if 1-naphthalenesul-fonic acid is added to moderately concentrated sulfuric acid (20-60%). This greatly reduces the evolution of nitrous fumes compared with a solution of pure sulfuric acid of the same hydrogen ion concentration. It has not yet been investigated whether the phenomenon is due to the formation of an ion pair, [C10H7 —SO NO+], or whether it is simply a solubility effect. In any case, the total acidity range of 4-12 m has thereby become available for diazotization technically crude sulfonation mixtures are used after dilution with water, for example, a solution of total acidity 4 m, of which 2.7 m is due to sulfuric acid. A further advantage of the method lies in the stabilizing effect of the naphthalenesulfonic acid on the diazonium compounds formed (see Sec. 2.3). 

Salts of diazonium ions with certain arenesulfonate ions also have a relatively high stability in the solid state. They are also used for inhibiting the decomposition of diazonium ions in solution. The most recent experimental data (Roller and Zollinger, 1970 Kampar et al., 1977) point to the formation of molecular complexes of the diazonium ions with the arenesulfonates rather than to diazosulfonates (ArN2 —0S02Ar ) as previously thought. For a diazonium ion in acetic acid/water (4 1) solutions of naphthalene derivatives, the complex equilibrium constants are found to increase in the order naphthalene < 1-methylnaphthalene < naphthalene-1-sulfonic acid < 1-naphthylmethanesulfonic acid. The sequence reflects the combined effects of the electron donor properties of these compounds and the Coulomb attraction between the diazonium cation and the sulfonate anions (where present). Arenediazonium salt solutions are also stabilized by crown ethers (see Sec. 11.2). 

Apart from complex formation involving metal ions (as discussed in Chapter 4), crown ethers have been shown to associate with a variety of both charged and uncharged guest molecules. Typical guests include ammonium salts, the guanidinium ion, diazonium salts, water, alcohols, amines, molecular halogens, substituted hydrazines, p-toluene sulfonic acid, phenols, thiols and nitriles. 

The formation of bonds to aromatic rings is the foundation of much of organic synthesis. There has been much excitement over the past several years around Pd- or Cu-mediated displacement of an aromatic halide or aryl sulfonate with an amine. Paul Knochel of the University of Munich reports (Angew. Chem. Int. Ed. 2004,43, 897) a complementary approach, the addition of an aryl halide-derived Grignard such as 2 to the diazonium derivative 3. Aryl triflates such as 4 are efficient partners for further coupling. 

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