Hydrochloric Acid → methyl 4-hydroxy-2H-1,2-benzothiazine-3-carboxylate 1,1-dioxide

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Reaction Conditions

Reaction Steps

In a nitrogen atmosphere, a solution of 30 grams (0.117 moles) of methyl-2,3-dihydro-3-oxo-1,2-benzisothiazoline-2-acetate 1,1-dioxide in 50 ml DMF is added, with stirring, to a suspension of 18.9 grams (0.351 moles) of sodium methoxide in 100 ml DMF over a period of about 5 minutes and the internal temperature is maintained at 15°-30°C. by means of an ice bath. The stirring acidification continued for 30 minutes at about 30°C. after the completion of the addition. With external cooling, a solution of 35 ml concentrated HCl in 600 ml of water is added, maintaining the internal temperature below 35°C. After this addition, the mixture is cooled to 10°C. and filtered. The filter cake is washed thoroughly with water and the product is dried. Yield is 23.5 grams (78.2%) m.p. 173°-175°C. The total addition and stirring time prior to acidification should be less than 1 hour. For example, if the addition should take 30 minutes the batch should be stirred only an additional 15-20 minutes.

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