Frémy's salt is a chemical compound with the formula (K4[ON(SO3)2]2), sometimes written as (K2[NO(SO3)2]). It is a bright yellowish-brown solid, but its aqueous solutions are bright violet. The related sodium salt, disodium nitrosodisulfonate (NDS, Na2ON(SO3)2, CAS 29554-37-8) is also referred to as Frémy's salt. Regardless of the cations, the salts are distinctive because aqueous solutions contain the radical [ON(SO3)2]2−.

Applications

Frémy's salt, being a long-lived free radical, is used as a standard in electron paramagnetic resonance (EPR) spectroscopy, e.g. for quantitation of radicals. Its intense EPR spectrum is dominated by three lines of equal intensity with a spacing of about 13 G (1.3 mT). The inorganic aminoxyl group is a persistent radical, akin to TEMPO. It has been used in some oxidation reactions, such as for oxidation of some anilines and phenols allowing polymerization and cross-linking of peptides and peptide-based hydrogels. It can also be used as a model for peroxyl radicals in studies that examine the antioxidant mechanism of action in a wide range of natural products.

Preparation

Frémy's salt is prepared from hydroxylaminedisulfonic acid. Oxidation of the conjugate base gives the purple dianion: The synthesis can be performed by combining nitrite and bisulfite to give the hydroxylaminedisulfonate. Oxidation is typically conducted at low-temperature, either chemically or by electrolysis. Other reactions:

History

Frémy's salt was discovered in 1845 by Edmond Frémy (1814–1894). See: