Fremy s Salt, potassium

Juglone is most readily synthesized by Bemthsen s method. However, this method is too drastic and results in low yields (56). Somewhat better yields are obtained by using Fremy s salt (potassium nitroso disulfonate) as the oxidant (57). By using thallium trinitrate to oxidize 1,5-dihydroxynaphthalene, yields as high as 70% of juglone have been reported (58). 

DPPH- has an intense absorption maximum around 520 run (Yordanov and Christova, 1997), and antioxidant capacity and activity measured by the reduction of DPPH- are easily quantified by VIS-spectroscopy (Brand-Williams et al, 1995 Bondet et al, 1997, Espin et al, 2000). The stable radicals Fremy s salt (potassium nitrosodisulphonate) and galvinoxyl (2,6-di-tert-butyl-a-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-l-ylidene)-p-tolyloxy radical) have been used in a similar manner but with ESR detection, which can be used with samples that are not optically transparent (Gardner et al, 1998). 

In addition to the aforementioned syntheses of various carbazole-l,4-quinone alkaloids, many formal syntheses for this class of carbazole alkaloids were also reported. These syntheses involve the oxidation of the appropriate 1- or 4-oxygenated-3-methylcarbazoles using Fremy s salt (potassium nitrosodisulfonate), or PCC (pyridinium chlorochromate), or Phl(OCCXI F3)2 [bis(trifluoroacetoxy)iodo]-benzene. Our iron-mediated formal synthesis of murrayaquinone A (107) was achieved starting from murrayafoline A (7) (see Scheme 5.34). Cleavage of the methyl ether in murrayafoline A (7) and subsequent oxidation of the resulting intermediate hydroxycarbazole with Fremy s salt provided murrayaquinone A (107) (574,632) (Scheme 5.113). 

Reduction of ketone (81) with zinc and acetic acid produced the 4-hydroxypyrazoles (87), whereas reaction with dithionite gave the corresponding 1,4-dihydroxypyrazoles (88). These compounds could be oxidized with Fremy s salt (potassium nitrosodisulfonate) to the 3,4-diazacyclopentadienone 3-oxides. 

Oxidation of 2,2-dimethylthiochroman-4-ones to the 3,4-diones is readily achieved with isoamyl nitrite <1994T7865> and 8-hydroxy-2,2-dimethylthiochroman-4-one with Fremy s salt, potassium nitrodisulfonate, yields the benzothiopyranoquinone 387. Following cycloaddition with a cyclohexa-1,3-diene, enolization, oxidation, and aromatization led to a naphtho[2,3-A]-thiopyranoquinone (Scheme 103) <1997TL153, 2000H(53)585>. 

Mattocks has described a new method for oxidizing retronecine (27) to the unstable dihydropyrrolizine (28), using Fremy s salt (potassium nitroso-disulphonate).13... 

Fremy s salt (potassium nitrodisulfonate) is a widely used reagent, particularly in the synthesis of quinone antibiotics. One example has emerged from Kozikowski s group in their approach to the rubra-dirin antibiotics. The MEM-protected 2-nitroresorcinol (4) was converted in several steps to the phenol... 

Quinones can he prepared hy the oxidation of phenols, dihydroxy-henzenes, dimethoxyhenzenes and anilines. For example, 1,4-dihydroxy-henzene (hydroquinone) can he oxidized in good yield using sodium chlorate in dilute sulfuric acid in the presence of vanadium pentoxide and also hy manganese dioxide and sulfuric acid and hy chromic acid. Other reagents which convert hydroquinones to quinones include Fremy s salt [potassium nitrosodisulfonate, (KS03)2N0] and cerium(IV) ammonium nitrate [CAN, Ce(NH4)2(N03)J. 

There is also the classic case of Fremy s salt (potassium nitrosodisulfonate), prepared as follows ... 

Fig. 2 Chemical structures of common nitroxide spin probes Fremy s salt (potassium nitrosodi-sulfonate) TEMPO and derivatives (2,2,6,6-tetramethylpiperidine-l-oxyl), DOXYL (4,4-dimethyl-oxazolidine-l-oxyl) PROXYL (2,2,5,5-tetramethylpyrrolidine-l-oxyl) Dehydro-PROXYL (2,2,5,5-tetramethylpyrroline-l-oxyl) 5-DSA (5-DOXYL stearic acid) 16-DSA (16-DOXYL stearic...

A new mild and stepwise dehydrogenation of tetrahydroisoquinolines involves the use of Fremy s salt (potassium nitrosodisulfonate) at room temperature. Best results were obtained when no substituent or only small alkyl substituents were present at... 

Phenols don t undergo oxidation in the same way that alcohols do because they don t have a hydrogen atom on the hydroxyl-bearing carbon. Instead, oxidation of a phenol yields a cyclohexa-2,5-diene-l,4-dione, or quinone. The most commonly used oxidant is Fremy s salt [potassium nitrosodisulfonate, (KSOalaNO], and the reaction takes place through a radical mechanism. 

Phenols are aromatic counterparts of alcohols but are much more acidic (pkia 10) because their anions are resonance stabilized by delocalization of the negative charge into the aromatic ring. Phenols can he oxidized to quinones by reaction with Fremy s salt (potassium nitrosodisulfonate), and quinones can he reduced to hydroquinones by reaction with NaBH4. 

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