o-Phenylenediamine (OPD) is widely used in various industrial and scientific applications. It serves as a key intermediate in the production of dyes and pigments, particularly for hair dyes, textiles, and fur coloring, due to its ability to form stable and vibrant colors. In analytical chemistry, OPD is employed as a substrate in enzymatic assays, especially in ELISA (Enzyme-Linked Immunosorbent Assay) tests, where it reacts with hydrogen peroxide to produce a measurable color change, aiding in the detection of antibodies or antigens. Additionally, it is utilized in the synthesis of polymers and corrosion inhibitors, offering protective properties for metals. Its role in organic synthesis also extends to the creation of pharmaceuticals and agrochemicals, where it acts as a building block for complex molecules.