Preparation of p-aminoazo-benzene from aniline

In a process for the preparation of p-aminoazobenzene which comprises the steps of reacting an excess of aniline with an alkali metal nitrite in a hydrochloric acid medium at a temperature below 100.degree. C., isomerizing the resulting diazoamino compound in the same medium, neutralizing the reaction mixture, and separating the resulting aqueous phase from the organic phase which contains the formed p-aminoazobenzene dissolved in aniline, the improvement comprising effecting the aforesaid reaction in the presence of a compound selected from the group consisting of acrylonitrile, methacrylonitrile, methacrylic acid, alkyl methacrylate with 1 to 4 carbon atoms in the alkyl radical, and butadiene, in an amount of at least about 0.1% but not more than 20% by weight, based on the aniline.