Frémy's salt is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula (K₄ N(SO₃)₂sub>2), sometimes written as (K₂ O(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 Radical (from Latin: ', root) may refer to: Politics and ideology Politics *Classical radicalism, the Radical Movement that began in late 18th century Britain and spread to continental Europe and Latin America in the 19th century *Radical politics ...

N(SO₃)₂sup>2−.

Applications

Frémy's salt, being a long-lived free radical, is used as a standard in

electron paramagnetic resonance Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a method for studying materials that have unpaired electrons. The basic concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but the spin ...

(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 Aminoxyl denotes a radical functional group with general structure R2N–O•. It is commonly known as a nitroxyl radical or a nitroxide, however IUPAC discourages the use of these terms, as they erroneously suggest the presence of a nitro group. ...

is a persistent radical, akin to

TEMPO In musical terminology, tempo (Italian for 'time'; plural 'tempos', or from the Italian plural), measured in beats per minute, is the speed or pace of a given musical composition, composition, and is often also an indication of the composition ...

. 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

hydrogel A hydrogel is a Phase (matter), biphasic material, a mixture of Porosity, porous and Permeation, permeable solids and at least 10% of water or other interstitial fluid. The solid phase is a water Solubility, insoluble three dimensional network ...

s. 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 Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

of the

conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid gives a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as it loses a hydrogen ion in the reve ...

gives the purple

dianion A dianion is an anion with a net charge of −2. While there exist many stable molecular dianions, such as and , thus far no stable atomic dianion has been found: Electron shielding and other quantum mechanical effects tend to make the addition o ...

: :HON(SO₃H)₂ → ON(SO₃)₂sup>2− + 2 H⁺ :2 ON(SO₃)₂sup>2− + PbO₂ → 2 N(SO₃)₂sup>2− + PbO + H₂O The synthesis can be performed by combining

nitrite The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...

and

bisulfite The bisulfite ion (IUPAC-recommended nomenclature: hydrogensulfite) is the ion . Salts containing the ion are also known as "sulfite lyes". Sodium bisulfite is used interchangeably with sodium metabisulfite (Na2S2O5). Sodium metabisulfite diss ...

to give the hydroxylaminedisulfonate. Oxidation is typically conducted at low-temperature, either chemically or by

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses Direct current, direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of c ...

. Other reactions: : HNO₂ + 2 → + H₂O : 3 + + H⁺ → 3 + MnO₂ + 2 H₂O : 2 + 4 K⁺ → K₄ N(SO₃)₂sub>2

History

Frémy's salt was discovered in 1845 by

Edmond Frémy Edmond Frémy (; 28 February 1814 – 3 February 1894) was a French chemist. He is perhaps best known today for Frémy's salt, a strong oxidizing agent which he discovered in 1845. Fremy's salt is a long-lived free radical that finds use as a s ...

(1814–1894).See: * Frémy, E. (1845
"Sur un nouvelle série d'acides formés d'oxygène, de soufre, d'hydrogène et de d'azote"
(On a new series of acids formed from oxygen, sulfur, hydrogen, and nitrogen), ''Annales de Chimie et de Physique'', 3rd series, 15 : 408-488. Frémy's salt appears o
p. 447
where it's called ''"sulfazidate de potasse"''. * Frémy, E. (1845
"Sur un nouvelle série d'acides formés d'oxygène, de soufre, d'hydrogène et de d'azote"
(On a new series of acids formed from oxygen, sulfur, hydrogen, and nitrogen), ''Comptes rendus'', 21 : 218–226. This is a condensed version of the article that appeared in ''Annales de Chimie et de Physique''. * "Séances académiques," ''L'Institut'', no. 604, 23 July 1845
pp. 265–266.
* "Séances académiques," ''L'Institut'', no. 619, 12 November 1845
pp. 393.
Here a committee of the French Academy of Sciences reviewed Frémy's findings. * Edward Divers and Tamemasa Haga (1900
"Identification and constitution of Frémy's sulphazotised salts of potassium,"
''Journal of the Chemical Society, Transactions'', 77 : 440-446
doi:10.1039/CT9007700440
Here, correct formulae for Frémy's salts are presented. O
p. 445
the salt that Frémy called ''sulfazidate'' is identified as ON(SO₃K)₂. Its use in organic synthesis was popularized by Hans Teuber, such that an oxidation using this salt is called the Teuber reaction.

Applications

Preparation

History

References

Further reading