[C:1]([CH2:4][N:5]1[C:9]2[CH:10]=[CH:11][CH:12]=[CH:13][C:8]=2[S:7][C:6]1=[S:14])([OH:3])=[O:2].[C:15](=O)(O)[O-].[Na+]>CO>[S:14]=[C:6]1[N:5]([CH2:4][C:1]([O:3][CH3:15])=[O:2])[C:9]2[CH:10]=[CH:11][CH:12]=[CH:13][C:8]=2[S:7]1To a stirred solution containing 45.1 g (0.2 mol) of 3-(carboxymethyl) benzothiazoline-2-thione in 600 ml of methyl alcohol, 142.0 g (1.0 mol) of boron trifluoride ether complex was added in one portion. An exothermic reaction set in causing a temperature rise from 20° to 37° C. The stirred solution was heated at reflux for 24 hours and then cooled to 0° C. After cooling, 1400 ml of 10% aqueous sodium bicarbonate was slowly added (foaming observed) at 0°-10° C. until pH 8 was obtained. After stirring at 0°-10° C. for one hour, the solid was collected by filtration, washed with water until neutral to litmus and air-dried at 25°-30° C. The product, 2-thioxo-3(2H)-benzothiazoleacetic acid, methyl ester was obtained in 94% yield, m.p. 127°-128° C.
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