Dipotassium nitrosodisulfonate,

OXIDATION WITH THE NITROSODISULFONATE RADICAL. II. USE OF DIPOTASSIUM NITROSODISULFONATE (FREMY S SALT) 4,5-DIMETHYL-1,2-BENZ0QUIN0NE, 52, 88... 

The submitters report that approximately half of the nitrosodisulfonate radical had decomposed after the solution was stored at 0° for 2 weeks. They report the following procedure for the isolation of Fremy s salt (dipotassium nitrosodisulfonate). 

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. " ... 

Solutions of the nitrosodisulfonate salts are most stable in weakly alkaline solutions (pH 10) and decompose rapidly when the solution is acidic or strongly alkaline. The solid- dipotassium nitrosodisulfonate (Fremy s salt) has been reported to procedures involving the use of substantial quantities of the dry solid salt may be hazardous. In the present procedure, separation and use of the solid salt is avoided since the disodium nitrosodisulfonate is formed and used in aqueous solution. In this procedure, 2 moles of the preformed nitrosodisulfonate salt are consumed in the oxidation of one mole of the phenol to the benzoquinone huivative. The submitters report that only one molar equivalent of the nitrosodisulfonate salt is required if the electrochemical oxidation is carried out in the presence of a heptane solution of the phenol. 

Oxidation of appropriate mono- and di-hydroxyquinolines leads to quinones. This can be achieved by a variety of oxidizing agents including chromic acid and Fremy s salt (dipotassium nitrosodisulfonate, (KS03)2N0-) (67CB2077, 67CB2918). Examples are shown in Scheme 92. 9-Acridonequinones result from analogous oxidations of dihydroxy-9-acridones. 

Stable Free Radicals. Stable free radicals are a small minority of the more than 6 million chemical compounds known by 2005. The oxygen molecule is paramagnetic (S = 1). In 1896, Ostwald stated that "free radicals cannot be isolated." Only four years later, Gomberg123 made triphenylmethyl (Fig. 11.63), the first proven stable and persistent free radical [48] An infinitely stable free radical used as a reference in EPR is diphenyl-picryl hydrazyl (DPPH). Other persistent free radicals are Fremy s124 salt (dipotassium nitrosodisulfonate K+ O3S-NO-SO3- K+) 2,2-diphenyl-l-picrylhydrazy (DPPH)l, Galvinoxyl (2,6-di-tert-butyl-a-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-l-ylidene)-p-... 

The oxidation of phenols with Fremy s radical, dipotassium nitrosodisulfonic acid [N0(S03K)2, 7.34], to hydroquinones is known as the Teuber reaction . The disodium salt of nitrosodisulfonic acid [N0(S03Na)2] is also used for the oxidation of phenols. 

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