Hydrogen Peroxide → (+)-1-{2,4-dimethyl-5-[(2,2,2-trifluoroethyl)sulphinyl]phenyl}-3-(trifluoromethyl)-1H-1,2,4-triazole

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In a three-neck flask, 10.3 g (27.54 mmol, 95% pure) of 1-{2,4-dimethyl-5-[(2,2,2-trifluoroethyl)sulphanyl]phenyl}-3-(trifluoromethyl)-1H-1,2,4-triazole and 145.8 mg (0.55 mmol) of vanadium acetylacetonate were dissolved in 36 ml of chloroform and stirred for 10 minutes. Subsequently, 275.8 mg (0.825 mmol) of (S)-(2,4-di-tert-butyl-6-{(E)-[(1-hydroxy-3,3-dimethylbutan-2-yl)imino]methyl}phenol were added. After 10 minutes, 5.66 g (50 mmol) of 30% H2O2 were metered in over 6 hours. The progress of the conversion was monitored by means of HPLC. After 4 h of reaction time, a further 145.8 mg (0.55 mmol) of vanadium acetylacetonate and 275.8 mg of (2,4-di-tert-butyl-6-{(E)-[(1-hydroxy-3,3-dimethylbutan-2-yl)imino]methyl}phenol in 4 ml of chloroform were metered in. Subsequently, 40 ml of chloroform, 20 ml of water and 20 ml of thiosulphate solution were added successively. After the aqueous phase had been removed, the organic phase was washed with water and dried over Na2SO4, and the solvent was evaporated under reduced pressure. This gave 10.84 g of grey-brown crystals of (+)-1-{2,4-dimethyl-5-[(2,2,2-trifluoroethyl)sulphinyl]phenyl}-3-(trifluoromethyl)-1H-1,2,4-triazole (98% yield, 93.1% HPLC purity) with 2.81% sulphone content. The enantiomeric excess was determined by means of HPLC on a chiral phase (Daicel Chiracel OJ-RH 150) with a ratio of 16.34:83.66.

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