Dipotassium nitrosodisulfonic acid

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. 

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. 

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