Fremys Salt

By means of Fremy salt oxidation, Adler and Lundquist (5) estimated that about half of the phenolic units contain free S-positions in M.W.L. Mikawa (J/), by Mannich reaction, obtained evidence that about 25-40% of the phenolic units in his sulfate lignin preparation contained no substituent in 5-position. In this investigation we also conclude that at least one-third of the phenolic units in our kraft lignin preparation has free 5-positions. 

K. The three markers at the bottom are the positions of the Fremy Salt resonances, withyf = 2.0056 and = 2.0056. (B) to (E) are spectra used as benchmarks for deconvolution of the DNA spectrum. (B) One-electron oxidized guanine. (C) One-electron reduced cytosine (i.e. the protonated anion radical). (D) Thymine anion radical. (E) Composite spectrum of neutral sugar radicals. 

Potassium nitrosodisulfonate (Fremy salt), 0N(S03K)2, is a free radical capable of converting phenols [487, 488, 489 and aromatic amines [490 into quinones. 

Conversion to ortho- and para-quinones is by far the most common oxidation of phenols. Mercuric oxide or mercuric trifluoroacetate [583], lead dioxide [430], chromium trioxide [559], bromine [732], 2,3 dichloro-5,6-dicyano-/> benzoquinone (DDQ) [977], Fremy salt [487, 488, 489], and hydrogen peroxide in the presence of horseradish peroxidase [7958] are the most widely used oxidants (equations 310 and 311). 

Tribromo-m-cresol is oxidized by chromium trioxide in 70% acetic acid at 70-75 °C within 10 min to dibromo-m-toluquinone (3,5-dibromo-2-methyl-p-benzophenone) in 77% yield [559]. 2-BVomo-4-hy-droxy-5-methoxybenzyl alcohol treated with Fremy salt at pH 6 at room temperature for 1 h gives an 84% yield of 2-bromo-5-methoxy -benzo-quinone [487]. 4-Benzyl-2,6-dibromophenol, on oxidation with bromine in a sealed tube, yields 2,6-dibromophenylchinomethide [732] (equation 312). The oxidation of 2,5-di-tert-butyl-4-methoxyphenol with mercuric oxide or... 

The presence of an amino group on an aromatic ring often results in oxidation of the ring to a quinone. The classical and industrial method is the treatment of anilines with potassium dichromate and sulfuric acid. Thus, aniline at room temperature is converted into p-benzoquinone in 86% yield [647], and 2,5-dimethylaniline at 80 °C gives a 55% yield of p-xyloquinone [648. A specific reagent for such oxidations is the Fremy salt, potassium nitrosodisulfonate (equation 528) [490. The oxidation of the amino group takes place even if it is acylated (equation 529) [1190. ... 

OXIDATION WITH POTASSIUM NITROSODISULFONATE (FREMY SALT)... 

Figure 7. ESR spectra of radicals derived from N-acetyl-iL-alanine in an irradiated D20 ice plug. Sample contained 190 mg/ml of N-acetylalanine and was irradiated to 5 kGy at —196°C. Spectrum a was recorded at —196°C spectra b and c at —135°C. All spectra have markers from Fremys salt superimposed. (a) Composite spectrum of radicals present after annealing at —153°C (approximately 65% corresponds to the anion), (b) Composite spectrum of the radicals formed upon annealing the ice plug to — 80°C, of which 55% corresponds to the fatty acid radical, -CH(CHS)C02. (c) Spectrum of the peptide radical, CHsC0NDC(CHs)C02, formed upon further annealing the ice plug...

The phenolic ring in estrone can be readily oxidized. Reaction of estrone with Fremy salts (peroxylamine disulfonate) affords a mixture of the two isomeric catechols. In a more controlled manner, treatment of estrone with 2-iodoxybenzoic acid (22-1) leads intially to a mixture of the 2,3-quinone (22-2) and its 3,4-isomer (22-3) (Scheme 3.22). These products are then reduced in situ with ascorbic acid to afford 2-hydroxyestrone (22-4) and 4-hydroxyestrone (22-5). 

Oxidation of phenols or anilines to quinones by means of potassium nilrosodlsutlonate (Fremys salt). 

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