DiSulfonate, potassium nitroso

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). 

To this solution is added 90 g. (0.33 mole) of potassium nitroso-disulfonate (Fremy s salt) (Note 2). The mixture is shaken to dissolve the inorganic radical. A solution of 16 g. (0.131 mole) of 3,4-dimethylphenol (Note 3) in 350 ml. of ether is added quickly to the purple solution. The mixture is shaken vigorously for 20 minutes (Note 4). The color of the solution changes to red-brown. The o-quinone thus formed is subsequently extracted in three portions with a total of 1.2 1. of chloroform. The combined organic layers are dried over anhydrous sodium sulfate (Note 5), filtered, and evaporated under reduced pressure at 20-23° (Note 6). The residual, somewhat oily red-brown crystals are slurried twice with 15 ml.-portions of ice-cold ether and collected on a filter. The remaining dark red crystals, after air drying, weigh 8.7-8.9 g. (49-50%), m.p. 105-107° (Note 7). 

The preparation and use of Fremy s reagent, potassium nitroso-disulfonate, (KS03)2N-0, a stable free radical, is described (4). 

Dehydrogenation of enediones. The adduct (1) of 2,3-dimethoxyquinone and 1,3-dimethoxycyclohexa-l,3-diene is converted into the quinone (2) by enoliza-tion with potassium hydrogen carbonate and oxidation with potassium nitroso-disulfonate. The ethano bridge is lost on pyrolysis at 150° to give the tetramethyl ether of spirochrome-B (3).1... 

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