Ethanesulfinic acid sodium salt is an organosulfur compound with the chemical formula C₂H₅SO₂Na. It is the sodium salt of ethanesulfinic acid, characterized by the presence of a sulfinate functional group (-SO₂⁻). This white to off-white solid is typically hygroscopic and soluble in water and polar organic solvents. This compound serves primarily as a versatile reagent in organic synthesis. The sulfinate anion is a useful nucleophile and can act as a precursor for the generation of sulfonyl radicals. It is employed in various reactions, including sulfonylation, cross-coupling, and as a building block for the synthesis of more complex sulfone and sulfonamide derivatives. Its applications are foundational in medicinal chemistry and materials science research for constructing sulfur-containing molecular scaffolds. As a specialized synthetic building block, it is not a commodity chemical with broad industrial applications. Handling requires standard laboratory precautions, as it may cause irritation to the skin, eyes, and respiratory system. It should be stored in a cool, dry place under an inert atmosphere to prevent degradation due to its sensitivity to moisture and oxidation.