Fremy s Salt, potassium nitrosodisulfonate

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. 

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 ... 

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. 

Hydroxylamine trisulfonates, e.g. (K03S)0N-(S03K)2 are made by the reaction of K2SO3 with potassium nitrosodisulfonate (Fremy s salt). Acidification of the product results in rapid hydrolysis to the 0,A-disulfonate which can be isolated as the exclusive product ... 

The nitrosodisulfonate salts, particularly the dipotassium salt called Fremy s salt, are useful reagents for the selective oxidation of phenols and aromatic amines to quinones (the Teuber reaction). - Dipotassium nitrosodisulfonate has been prepared by the oxidation of a hydroxylaminedisulfonate salt with potassium permanganate, " with lead dioxide, or by electrolysis. This salt is also available commercially. The present procedure illustrates the electrolytic oxidation to form an alkaline aqueous solution of the relatively soluble disodium nitrosodisulfonate. This procedure avoids a preliminary filtration which is required to remove manganese dioxide formed when potassium permanganate is used as the oxidant. " ... 

Potassium nitrosodisulfonate (Fremy s salt), K(S03>2N0 Oxidizes phenols to yield quinones (Section 17.10). 

A solution of potassium nitrosodisulfonate (Fremy s salt) (0.56 mmol) dissolved in 5 ml water was added to a solution of the product from Step 7 (0.18 mmol) dissolved in 5 ml dioxane, the mixture stirred at ambient temperature 2 hours, and concentrated. The material was purified by reverse phase chromatography and the product isolated in 54% yield having a HPLC retention time of 1.75 minutes. 

Potassium nitrosodisulfonate (Fremy s Salt) [14293-70-0] M 268.3. It forms yellow needles (dimeric) which dissolve in H2O to give the violet monomeric free radical. It is purified by dissolving ( 12g) in... 

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