4-Nitrosodiphenylamine is primarily used as a chemical intermediate in the synthesis of dyes and pigments. It plays a crucial role in the production of azo dyes, which are widely utilized in the textile, leather, and paper industries for coloring purposes. Additionally, it has been employed in the manufacture of rubber chemicals, where it acts as an antioxidant and antiozonant to protect rubber products from degradation caused by exposure to oxygen and ozone. Its application extends to research and development, where it serves as a reagent in organic synthesis and chemical studies.