This dimer of aniline has various industrial uses, including as a hair dye ingredient, but also has raised concerns about toxicity by skin contact.

[1] It is also a starting material for the synthesis of 6PPD, an antiozonant for various rubber products.

[2] A colorimetric test for the quantitative analysis of nitrite, at levels below 100 nanograms per milliliter, is based on nitrite-catalyzed coupling of 4-aminodiphenylamine with N,N-dimethylaniline.

[3] The most common route of industrial production is by the metal catalysed reaction of aniline with 4‑nitrochlorobenzene to give 4‑nitrodiphenylamine (Buchwald–Hartwig amination): Subsequent hydrogenation gives 4-aminodiphenylamine.

[5][6] This again requires a reduction step but is a good example of industrial green chemistry as it eliminates the need for organochlorine starting materials and metal catalysts.