[OH:1][N:2]1[C:7]([CH3:9])([CH3:8])[CH2:6][C:5](=[O:10])[CH2:4][C:3]1([CH3:12])[CH3:11].[C:13](#N)[CH3:14].OO.S([O-])([O-])=O.[Na+].[Na+]>O.O.C(O)(=O)CC(CC(O)=O)(C(O)=O)O.C1CCCCC1>[CH:14]1([O:1][N:2]2[C:7]([CH3:8])([CH3:9])[CH2:6][C:5](=[O:10])[CH2:4][C:3]2([CH3:12])[CH3:11])[CH2:13][CH2:5][CH2:4][CH2:3][CH2:11]1
A solution of 0.104 g (0.523 mmol) of ferrous chloride tetrahydrate and 0.168 g (0.799 mmol) of citric acid monohydrate in 1.5 ml of water is added to a mixture of 3.14 g (18.4 mmol) of 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one, 30 ml of acetonitrile, and 20 ml of cyclohexane that has been heated to the reflux temperature of 60°. A solution of 5.27 g (77 mmol) of 50% aqueous hydrogen peroxide is added dropwise over 2 hours to the reaction mixture while the temperature is maintained at reflux. A solution of 0.047 g of ferrous chloride tetrahydrate and 0.055 g of citric acid monohydrate in 0.5 ml of water is added to the reaction mixture 1.6 hours after the peroxide addition is started. After the peroxide is added, the reaction mixture is heated at reflux for 30 minutes, then allowed to cool slowly. Aqueous sodium sulfite solution is added to the reaction mixture to decompose excess peroxide. The aqueous layer is extracted with a 2:1 mixture of acetonitrile-cyclohexane and then with ethyl acetate. The combined organic layers are concentrated. Purification by flash chromatography with 20:1 heptane-ethyl acetate affords 3.01 g (64% yield) of the title compound as a colorless liquid. GC assay is 99%.
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