Nitric Acid → (4-Methoxy-7-nitro-benzothiazol-2-yl)-carbamic acid methyl ester

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To a stirred solution of 13.6 g (57.1 mmol) (4-methoxy-benzothiazol-2-yl)-carbamic acid methyl ester in 300 ml acetic acid at room temperature was added 200 ml 65% nitric acid and the mixture heated at 70° C. for 4 h. The mixture was then poured onto stirred ice-water and the resulting slurry was filtered. The filter-cake was dissolved in THF and 5 N sodium hydroxide solution was added until the pH was 8. This mixture was then stirred for 1 h, filtered, and the filter-cake dried in vacuo to afford 7.61 g (47%) (4-methoxy-7-nitro-benzothiazol-2-yl)-carbamic acid methyl ester as a yellow crystalline solid. Meanwhile, the filtrate was separated into its aqueous and organic phases and the organic phase was dried over sodium sulfate and concentrated in vacuo. The residue was resuspended in 200 ml THF and 200 ml methanol and heated at 70° C. overnight. The mixture was then cooled to room temperature and the resulting crystals were collected by filtration, washed with THF, and dried in vacuo to afford a further 1.50 g (9%) of product as a yellow crystalline solid. ES-MS m/e (%): 306 (M+Na+, 28), 2,S4 (M+H+, 100).

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