Cl.[NH2:2][OH:3].C(=O)([O-])[O-].[Ba+2].[CH3:9][CH:10]1[CH:14]([C:15]([O:17][CH3:18])=[O:16])[C:13](=O)[CH:12]([CH3:20])[S:11]1>C(O)C>[OH:3][N:2]=[C:13]1[CH:12]([CH3:20])[S:11][CH:10]([CH3:9])[CH:14]1[C:15]([O:17][CH3:18])=[O:16]Hydroxylamine hydrochloride, 145 g (2.09 mol), and barium carbonate (J. T. Baker Chemical Company), 219.2 g (1.11 mol), are added to a solution of 89.3 g (0.474 mol) of tetrahydro-2,5-dimethyl-4-oxo-3-thiophenecarboxylic acid, methyl ester (Example C) in 1 L of absolute ethanol. The suspension is stirred and refluxed for sixteen hours, cooled, filtered through Supercell Hyflo® (Johns-Manville), the filtrate evaporated and the residue dissolved in 500 ml of diethyl ether. The diethyl ether solution is washed with 500 ml of water (2 times). The diethyl ether layer is separated, dried over anhydrous Na2SO4 and evaporated to give 83.7 g of tetrahydro-4-(hydroxyimino)-2,5-dimethyl-3-thiophene-carboxylic acid, methyl ester as an orange liquid.
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