Hydrogen Bromide → 2-bromomethyl-4-isopropyl-6-methoxy-1,2-benzisothiazol-3(2H)-one 1,1-dioxide

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A solution of 2-(pivaloyloxymethyl)-4-isopropyl-6-methoxy-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (1.33 kg, 3.62 mol), 48% HBr in acetic acid (1 L) and 3 L of acetic acid was stirred on a steam bath (90°-95° C.) for 1.5 hours. The solvent (acetic acid) was removed under vacuum to give a thick slurry of an off-white residue which was diluted with 10 L of cold water and stirred for 30 minutes. The crude product was collected by filtration, washed first with 6 L of water and then with 3 L of saturated sodium bicarbonate solution. The crude solid was dried at 60°-70° C. for 20 hours and then was recrystallized from a mixture of 5 L of ethyl acetate and 6 L of hexane. Two crops were collected to give 1.16 kg (92%) of 2-bromomethyl-4-isopropyl-6-methoxy-1,2-benzisothiazol-3(2H)-one 1,1-dioxide, as an off-white solid, m.p. 157°-159° C.

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