Used as a corrosion inhibitor in heating and cooling systems, particularly in glycol-based heat transfer fluids. It forms a protective oxide layer on metal surfaces, preventing oxidation and extending equipment life. Commonly applied in industrial boilers, closed-loop systems, and metalworking fluids. Also serves as a reagent in chemical synthesis, including dye and pharmaceutical production, due to its ability to introduce nitroso and nitro groups. In some cases, it is used in preservation and passivation treatments for metals. Requires careful handling due to potential formation of toxic fumes under acidic conditions.