Arenediazonium salt reaction with arylamines

Arenediazonium salts undergo a coupling reaction with activated aromatic rings such as phenols and arylamines to yield brightly colored azo compounds, Ar—N=N—Ar. ... 

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. 

The most useful reaction of amines with nitrous acid is the reaction of arylamines to form arenediazonium salts. We consider next how these diazonium salts may be used as synthetic intermediates. 

We have seen that primary arylamines react with nitrous acid to form stable arene-diazonium salts (Section 16.12). Arenediazonium salts are useful to synthetic chemists because the diazonium group can be replaced by a wide variety of nucleophiles. This reaction allows a wider variety of substituted benzenes to be prepared than can be prepared solely from electrophilic aromatic substitution reactions. 

There has been a theoretical study of the reaction of arenediazonium cations with azide anions, which yields arylazides. No evidence for the formation of arylpen-tazoles was found. Arenediazonium salts have been identified as intermediates in the palladium-catalysed Sonagashira reaction of arylamines with alkynes to give arylalkynes. Palladium catalysis has also been used in the synthesis of diarylheptanols by the reaction of 4-hydroxybenzenediazonium ions with dihydropyrans. ... 

The most important reaction of amines with nitrous acid, by far, is the reaction of primary arylamines. We shall see why in Section 20.7. Primary arylamines react with nitrous add to give arenediazonium salts. Even though arenediazonium salts are unstable, they are still far more stable than aliphatic diazonium salts they do not decompose at an appreciable rate in solution when the temperature of the reaction mixture is kept below 5°C ... 

The Pd°-catalyzed arylations using arenediazonium tetrafluoroborates are limited to those diazonium salts that can be manipulated at room temperature. The reaction can, if necessary, be performed at temperatures up to 50 °C by using a mixture of an arylamine and tert-butyl nitrite in chloroacetic acid or in a mixture of chloroacetic and acetic acid (Kikukawa et al., 1981a). Styrene reacted with fourteen arylamines in the presence of 5 mol-% Pd(dba)2 to give the corresponding substituted stilbenes in yields of 46-97%. It is important for good yields to carry out these reactions in an acidic system. Without acid the yield was low (11%), and diazo tars were also formed. 

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