Diazonium salts aryl nitriles

Linkers for Alkyl and Aryl Halides, Azides, Diazonium Salts, and Nitriles 115... 

Preparation of aryl nitriles Cop-per(l) cyanide converts aryl diazonium salts to aryl nitriles. 

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. 

Condensation of diazonium salts 1152 with activated nitriles provides hydrazones 1153. Treatment of hydrazones 1153 with hydroxylamine affords amidoximes 1154 in high yield. Upon heating with anhydrous sodium acetate in refluxing DMF, compounds 1154 undergo intramolecular cyclocondensation to provide 5-substituted 4-amino-2-aryl-277-1,2,3-triazoles 1155 in 75-85% yield (Scheme 190) <2006ARK(xv)53>. 

The Sandmeyer reaction utilizes a diazonium salt to produce an aryl halide. The process begins by converting an amine to a diazonium salt. Decomposition of the diazonium salt in the presence of a copper halide places the halide ion into the position originally occupied by the amine. The most useful copper halides are CuCl and CuBr in addition, the copper pseudohalides, such as CuCN, also works by placing a nitrile in the position originally occupied by the amine. Figure 13-27 shows an example of the Sandmeyer reaction. 

This valuable method for the preparation of aryl nitriles via the diazonium salt is discussed in Section 6.7.1, p. 922, and offers one of the most convenient routes for obtaining this class of compound. Experimental procedures are described in Expt 6.76. 

This route is particularly valuable for substituents that cannot easily be added by electrophilic substitution such as OH or CN. Table 2.2 gives you a selection of reagents. For the addition of CN, Cl or Br, copper (I) derivatives usually give the best results. So the aryl nitrile 46 might come from amine 47 via a diazonium salt and routine disconnections lead us back to toluene. 

Reaction mann reactions (Figure 16.4-16.6). Regarding the preparation of aromatic nitriles, this reaction presents an alternative to the Sandmeyer reaction of aryl diazonium salts with CuCN (cf. Figure 5.53). 

Ar—N=N diazonium salt CuCN Ar—C=N + aryl nitrile n2T (Section 19-17)... 

Diazonium salts are valuable reagents for the synthesis of aryl halides, nitriles, phenols, hydrazines and azo compounds. 

Many aryl nitriles are obtained from diazonium salts by treatment with copper(l) cyanide. Hydroxy and amino nitriles are obtained from addition reactions to carbonyl compounds. 

Aromatic nitriles generally cannot be prepared from the unreactive aryl halides (Sec. 25.5). Instead they are made from diazonium salts by a reaction we shall discuss later (Sec. 23.13). Diazonium salts are prepared from aromatic... 

As already mentioned, aromatic nitriles are made, not from the unrcactive aryl halides, but from diazonium salts (Sec. 23.13). 

Treatment of diazonium salts with cuprous, Cu(I), salts generates aryl halides. When 398 reacts with CuCl (cuprous chloride) or CuBr (cuprous bromide), the products are chlorobenzene or bromobenzene via what is probably a radical reaction.29l jhis conversion is known as the Sandmeyer reaction. 2 The use of copper powder rather than cuprous salts for this transformation is often called the Gattermann reaction. 93,292b,c Aryl iodides are also produced from diazonium salts by reaction with potassium iodide (KI) but the actual reactive species may be l3-.294,295 Treatment of aniline derivative 403 with sodium nitrite and HCl followed by treatment with KI, for example, gave a 89% yield of 404.Aryl nitriles are generated under Sandmeyer conditions using cuprous cyanide (CuCN), as in the conversion of 405 to benzonitrile derivative 407 via diazonium chloride, 406. 

Silyl and stannyl hydrides effect high yield reduction of aryl diazonium salts, and are compatible with a wider range of solvents than is HaP02. NaH prepared situ has been found to be much more active than the commercial product. Using the more active NaH, hydrogenolysis of benzylic halides is possible. Sodium borohydride has been reported to reduce nitriles to amines if Raney nickel is used as catalyst. 

Another common transformation of diazonium salts is their conversion to aryl halides by reaction with cuprous salts (CuX), in what is known as the Sandmeyer reaction, named after Traugott Sandmeyer (Switzerland 1854-1922). This means that the Ar-NH2 ArX conversion is possible, where Ar = an aryl group. When 132 is treated with cuprous bromide (CuBr), the product is bromobenzene (18). The reaction works with many other cuprous salts as well, including cuprous chloride (CuCl). A variation of this reaction treats the diazonirun salt with cuprous cyanide (CuCN) to give a nitrile. In this manner, 4-methylanihne (24) is treated with HCI and NaN02 and then with CuCN to give 4-methyl-l-cyanobenzene (134). 

---