Used in hair dye formulations as a coupler to produce stable, long-lasting color. It reacts with primary intermediates like p-phenylenediamine in oxidative dyes to form larger colored molecules within the hair shaft. Provides shades in the blue to violet range depending on the formulation. Offers good color intensity and resistance to fading from washing or UV exposure. Also used in some photographic developers and analytical reagents due to its reducing properties.