<Dd> ArNH + HNO + H → ArN + 2H O </Dd> <P> Aqueous solutions of diazonium chloride salts, traditionally prepared from the aniline, sodium nitrite, and hydrochloric acid, are unstable above 5 ° C. However, one can isolate diazonium compounds as tetrafluoroborate or tosylate salts, which are stable solids at room temperature . It is often preferred that the diazonium salt remain in solutions, but they do tend to supersaturate . Operators have been injured or even killed by an unexpected crystallization of the salt followed by its detonation . </P> <P> Due to these hazards, diazonium compounds are usually not isolated . Instead they are used in situ . This approach is illustrated in the preparation of an arylsulfonyl compound: </P> <P> The most widely practiced reaction of diazonium salts is azo coupling . In this process, the diazonium compound is attacked by, i.e., coupled to, electron - rich substrates . When the coupling partners are arenes such as anilines and phenols, the process is an example of electrophilic aromatic substitution: </P>

Preparation of benzoic acid from benzene diazonium chloride