Aniline reacts with a mixture of sodium nitrite and hydrochloric acid and forms benzene diazonium chloride.The structure of Benzene diazonium chloride is

Benzene diazonium chloride reacts with aniline in presence of dilute hydrochloric acid and undergoes coupling reaction and produces stable azo products. In this reaction, benzene diazonium chloride acts as an electrophile in coupling with activated aniline. In this type of reaction, substitution takes place at the para position. So, the reaction Benzene diazonium chloride with aniline in presence of dilute hydrochloric acid is as follows: