Frémy's salt
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| Template:Longitem | K2NO(SO3)2 |
| Molar mass | 268.33 g/mol (potassium salt) |
| Appearance | Yellowish-brown solid |
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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.[1][2] The related sodium salt, disodium nitrosodisulfonate (NDS, Na2ON(SO3)2, CAS 29554-37-8) is also referred to as Frémy's salt.[3]
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).[4][5][6]
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[7][8][9][10][11] allowing polymerization and cross-linking of peptides and peptide-based hydrogels.[12][13]
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.[14]
Preparation
Frémy's salt is prepared from hydroxylaminedisulfonic acid. Oxidation of the conjugate base gives the purple dianion:
- HON(SO3H)2 → [HON(SO3)2]2− + 2 H+
- 2 [HON(SO3)2]2− + PbO2 → 2 [ON(SO3)2]2− + PbO + H2O
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.[3][2]
Other reactions:
- HNO2 + 2 Template:Chem/link → Template:Chem/link + H2O
- 3 Template:Chem/link + Template:Chem/link + H+ → 3 Template:Chem/link + MnO2 + 2 H2O
- 2 Template:Chem/link + 4 K+ → K4[ON(SO3)2]2
History
Frémy's salt was discovered in 1845 by Edmond Frémy (1814–1894).[15] Its use in organic synthesis was popularized by Hans Teuber, such that an oxidation using this salt is called the Teuber reaction.[9][10]
References
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- ↑ Script error: No such module "citation/CS1". See page 463 for information on intensity measurements and page 86 for an EPR spectrum of Frémy's salt.
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- ↑ 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 on 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," Template:Webarchive Journal of the Chemical Society, Transactions, 77 : 440-446. doi:10.1039/CT9007700440 Here, correct formulae for Frémy's salts are presented. On p. 445, the salt that Frémy called sulfazidate is identified as ON(SO3K)2.
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Further reading
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