Phenols reaction with aryl diazonium, ions

A reaction of aryl diazonium salts that does not involve loss of nitrogen takes place when they react with phenols and arylamines Aryl diazonium ions are relatively weak elec trophiles but have sufficient reactivity to attack strongly activated aromatic rings The reaction is known as azo coupling two aryl groups are joined together by an azo (—N=N—) function... 

A reaction of aryl diazonium salts that does not involve loss of nitrogen takes place when they react with phenols and arylamines. Aryl diazonium ions are relatively weak... 

Examples of the three mechansims are, respectively (a) hydrolysis of aryl diazonium salts to phenols (b) reaction of aryl diazonium ions with Ns to give the aryl azides " and (c) the Sandmeyer reaction, involving cuprous chloride or bromide for synthesis of aryl halides. Specific synthetically important substitution processes are considered in the succeeding sections. 

Reaction of aryl diazonium ions with water gives phenols. 

Examples of the three mechanistic types are, respectively (a) hydrolysis of diazonium salts to phenols 82 (b) reaction with azide ion to form aryl azides 83 and (c) reaction with cuprous halides to form aryl chlorides or bromides.84 In the paragraphs which follow, these and other synthetically useful reactions of diazonium intermediates are considered. The reactions are organized on the basis of the group which is introduced, rather than on the mechanism involved. It will be seen that the reactions that are discussed fall into one of the three general mechanistic types. 

The problem now is to determine whether R is alkyl or aryl. It is known that primary aliphatic amines yield unstable diazonium compounds that immediately decompose to give nitrogen (N2) gas and a carbonium ion. The problem indicates that nitrogen gas is formed but only after a gradual warming to room temperature. It is known that primary aromatic amines (that have formed the diazonium compound) will yield the phenol under such conditions with the evolution of nitrogen gas. Hence, the only conclusion is that the unknown amine must be aromatic, since the reaction of the diazonium is gradual, not immediate. 

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