Phosphorus oxychloride → Pyridine-3-sulfonyl chloride

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Reaction Steps

Pyridine-3-sulfonic acid (125 g, 0.78 m) was placed in a 1 L, 3-necked flask equipped with mechanical stirrer, reflux condenser, thermometer and nitrogen inlet. Next, the phosphorus pentachloride (250 g, 1.19 m, 1.5 eq) was added, followed immediately by the phosphorus oxychloride (330 ml, 3.8 m, 4.5 eq). The contents of flask were initially stirred at ambient temperature for 30 min, then brought slowly to gentle reflux (internal temp. approx. 110° C.) over the next hour, kept at this temperature for approx. 3.5 hr then allowed over the next 12 hr to cool back to ambient temperature. Gas evolution was observed during this time. The volatiles were stripped under reduced pressure (at 12 mmHg/40° C.) and yellow semi-solid residue was diluted with DCM (1 L). The slurry was poured slowly into the stirred, ice-cold sat. aq. bicarbonate, maintaining pH=7. Gas evolution was observed. The organic layer was separated and aqueous layer was back-extracted with DCM. The combined extracts were washed with cold sat. aq. bicarbonate, brine and dried with magnesium sulfate. The solids were filtered off and filtrate evaporated, leaving pyridine-3-sulfonyl chloride as a pale yellow, oily liquid, 123 g (93% pure; 88% theory). 1H-NMR, CDCl3, (δ): 9.26 (d, 1H), 8.98 (dd, 1H), 8.34 (m, 1H), 7.62 (m, 1H). 13C-NMR, CDCl3, (8): 155.3, 147.4, 140.9, 134.6, 124.2.

Provenance & Evidence