In strongly basic conditions, benzenediazonium chloride is converted into diazohydroxide and diazoate as both of which are not electrophilic and do not couple with aniline.
`C_(6)H_(5)overset(+)(N)-=NC overset(-)(I)+OH SO_(2)underset("Diazohydroxide")(CH_(5)-N=N-OH)overset(NaOH)Leftrightarrow underset("Sodium diazonate")(C_(6)H_(5)-N=N-overset(-)(O)Na)` ltbRgt Similarly is highly acidic conditions aniline gets converted into anilium ion. From this, result aniline is no longer nucleophilic acid and hence will not couple with diazonium chloride. Hence the reaction is carried out under mild conditions i.e.pH-4-5
`underset("Aniline")(C_(6)H_(5)NH_(2)+H^(+)) to underset("Anillnium dion")(C_(6)H_(5)-overset(+)NH_(3))`
