弗氏鹽是一種無機化合物，化學式 (K4[ON(SO3)2]2)，有時寫作 (K2[NO(SO3)2])。它是一種亮黃棕色固體，但水溶液是亮紫色的。[1][2] 相關的鈉鹽亞硝基二磺酸鈉（簡稱NDS，化學式 Na2ON(SO3)2，CAS號 29554-37-8）也被稱為弗氏鹽。[3]
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弗氏鹽作為一種長壽命的自由基，是電子自旋共振 (EPR) 的標準。其強烈的EPR譜線由三條等強度的線主導，間距約為 13 G（1.3 mT）。[4][5][6]
弗氏鹽可用於某些氧化反應，例如某些苯胺或苯酚的氧化。[7][8][9][10][11]它也允許肽和基於肽的水凝膠的聚合和交聯。[12][13]
它還可以用作研究中過氧自由基的模型，以研究各種天然產品中抗氧化作用的機制。[14]
弗氏鹽可以由羥胺二磺酸開始製備而成。氧化它的共軛鹼可以得到紫色的雙陰離子：
- HON(SO3H)2 → [HON(SO3)2]2− + 2 H+
- 2 [HON(SO3)2]2− + PbO2 → 2 [ON(SO3)2]2− + PbO + H2O
羥胺二磺酸鹽則是由亞硝酸鹽和亞硫酸氫鹽反應而成的。氧化反應通常是在低溫下進行的，可以通過化學方法或電解達成。[3][2]
其它製備方法：
- HNO2 + 2 HSO−
3 → HON(SO
3)2−
2 + H2O
- 3 HON(SO
3)2−
2 + MnO−
4 + H+ → 3 ON(SO
3)2−
2 + MnO2 + 2 H2O
- 2 ON(SO
3)2−
2 + 4 K+ → K4[ON(SO3)2]2
弗氏鹽是在1845年由埃德蒙·弗雷米 (1814–1894)發現的。[15]
Wehrli PA, Pigott F. Oxidation with the nitrosodisulfonate radical. I. Preparation and use of sodium nitrosodisulfonate: trimethyl-p-benzoquinone. Organic Syntheses. 1972, 52: 83. doi:10.15227/orgsyn.052.0083. Wertz JE, Bolton JR. Electron Spin Resonance: Elementary Theory and Practical Applications. New York: McGraw-Hill. 1972. ISBN 978-0-07-069454-5. See page 463 for information on intensity measurements and page 86 for an EPR spectrum of Frémy's salt. Colacicchi S, Carnicelli V, Gualtieri G, Di Giulio A. EPR study of Frémy's salt nitroxide reduction by ascorbic acid; influence of bulk pH values. Res. Chem. Intermed. 2000, 26 (9): 885–896. S2CID 98775951. doi:10.1163/156856700X00372. Zielonka J, Zhao H, Xu Y, Kalyanaraman B. Mechanistic similarities between oxidation of hydroethidine by Frémy's salt and superoxide: stopped-flow optical and EPR studies. Free Radical Biology & Medicine. October 2005, 39 (7): 853–863. PMID 16140206. doi:10.1016/j.freeradbiomed.2005.05.001. Zimmer H, Lankin DC, Horgan SW. Oxidations with potassium nitrosodisulfonate (Frémy's radical). Teuber reaction.. Chemical Reviews. 1971, 71 (2): 229–246. doi:10.1021/cr60270a005. Islam I, Skibo EB, Dorr RT, Alberts DS. Structure-activity studies of antitumor agents based on pyrrolo[1,2-a]benzimidazoles: new reductive alkylating DNA cleaving agents. Journal of Medicinal Chemistry. October 1991, 34 (10): 2954–2961. PMID 1920349. doi:10.1021/jm00114a003. Teuber HJ. Use of dipotassium nitrosodisulfonate (Frémy's salt): 4,5-dimethyl-o-benzoquinone. Org. Synth. 1972, 52: 88. doi:10.15227/orgsyn.052.0088. Xue W, Warshawsky D, Rance M, Jayasimhulu K. A metabolic activation mechanism of 7H-dibenzo[c,g]carbozole via o-quinone. Part 1: synthesis of 7H-dibenzo[c,g]carbozole-3,4-dione and reactions with nucleophiles. Polycyclic Aromatic Compounds. 2002, 22 (3–4): 295–300. S2CID 95507636. doi:10.1080/10406630290026957. Wilchek M, Miron T. Mussel-inspired new approach for polymerization and cross-linking of peptides and proteins containing tyrosines by Frémy's salt oxidation. Bioconjugate Chemistry. March 2015, 26 (3): 502–510. PMID 25692389. doi:10.1021/bc5006152. 參見：
- Frémy, E. (1845) "Sur un nouvelle série d'acides formés d'oxygène, de soufre, d'hydrogène et de d'azote" （頁面存檔備份，存於網際網路檔案館） (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 （頁面存檔備份，存於網際網路檔案館）, 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" （頁面存檔備份，存於網際網路檔案館） (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. （頁面存檔備份，存於網際網路檔案館）
- "Séances académiques," L'Institut, no. 619, 12 November 1845, pp. 393. （頁面存檔備份，存於網際網路檔案館） 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," （頁面存檔備份，存於網際網路檔案館） 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 （頁面存檔備份，存於網際網路檔案館）, the salt that Frémy called sulfazidate is identified as ON(SO3K)2.
- Morey J. Undergraduate Experiments with a Long-Lived Radical (Frémy's salt): Synthesis of 1,4-Benzoquinones by Degradative Oxidation of p-Hydroxybenzyl Alcohols. J. Chem. Educ. 1988, 65 (7): 627–629. Bibcode:1988JChEd..65..627M. doi:10.1021/ed065p627.
