Hydrochloric Acid → 4-hydroxy-2H-naphtho[2,1-e]-1,2thiazine-3-carboxylic acid methyl ester-1,1-dioxide

Participants

Reaction Conditions

Reaction Steps

0.90 mol of methanol-free sodium methylate was prepared by dissolving 20.7 gm (0.90 gm-atom) of sodium in 350 ml of absolute methanol, subsequently distilling off the alcohol, and repeated azeotropic distillation with xylene. After addition of 9.15 gm (0.30 mol) of 3-oxo-naphth[2,1-d]isothiazoline-2-acetic acid methyl ester-1,1-dioxide, 250 ml of anhydrous tert.butanol were added. The reaction mixture was slowly heated to 60° C, kept at 60°-65° C for 11/4 hours, and subsequently refluxed for 1 hour. The mixture was allowed to cool, was then decomposed with ice and adjusted to a pH-value of 3-4 with concentrated hydrochloric acid. The solid product which formed was suction-filtered off, washed with water and dried, yielding 72.0 gm (78% of theroy) of 4-hydroxy-2H-naphtho[2,1-e]-1,2-thiazine-3-carboxylic acid methyl ester-1,1 -dioxide, m.p. 218°-220° C (after recrystallizing twice from ethylene chloride).

Provenance & Evidence