Sodium methanesulfinate is an organosulfur compound with the chemical formula CH3SO2Na. It is a white to off-white crystalline powder that is soluble in water and polar organic solvents. This compound serves as a versatile reagent in organic synthesis, primarily due to its role as a source of the methanesulfinate anion. Its most prominent application is as a mild and selective reducing agent. It is particularly effective for the reduction of organic peroxides to the corresponding alcohols and for the deoxygenation of amine N-oxides. Furthermore, it acts as a key building block for the introduction of the methylsulfonyl (MeSO2) group via sulfonylation reactions, such as in the synthesis of sulfones and sulfonamides. It is also employed in radical reactions and as a precursor for other sulfur-containing compounds. While not a mainstream pharmaceutical or agrochemical active ingredient, its utility is well-established in research and fine chemical synthesis laboratories for constructing complex molecules and performing specific functional group transformations.