Potassium Carbonate → 1,4-Dihydro-2,3-benzoxathiin-3-oxide

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Reaction Steps

Sodium hydroxymethanesulfinate (Rongalite™) (180 g; 1.17 mol) was suspended in DMSO (400 mL) and left to stir for 10 min. before dichloro-o-xylene (102.5 g; 0.59 mol), potassium carbonate (121.4 g; 0.88 mol) and sodium iodide (1.1 g; 7 mmol) were added consecutively. More DMSO (112 mL) was used to rinse residual materials into the reaction mixture before the whole was allowed to stir at room temperature. The initial endothermic reaction became mildly exothermic after around 1 h causing the internal temperature to rise to ca. 32-33° C. The reaction as followed by TLC (ethyl acetate/hexane, 50:50) and found to be complete after 3 h. The reaction mixture was diluted with methanol/ethyl acetate (20:80; 400 mL) and the solids were filtered off, and washed with more methanol/ethyl acetate (20:80; 100 mL, 2×50 mL). The filtrate was transferred to a separating funnel and brine (1 L) was added. This caused more sodium chloride from the product mixture to precipitate out. The addition of water (200 mL) redissolved the sodium chloride. The mixture was shaken and the organic layer was separated and then the aqueous layer was extracted further with methanol/ethyl acetate (20:80; 200 mL), 150 mL, 250 mL). The combined extracts were dried (Na2SO4) and rotary evaporated (bath 37-38° C.). More solvent was removed under high vacuum to give the sultine 10 as a pale orange liquid (126 g) that was found by 1H NMR spectroscopy to be relatively free of by-product but containing residual DMSO and ethyl acetate (FIG. 1).

Provenance & Evidence