氯磺酸是一类比较常用的直接氯磺化试剂，氯磺酸的活性比浓硫酸大，反应温度较低，同时可以直接得磺酰氯。氯磺化也是亲电反应，选择性也遵循芳环取代基定位效应及其规则。有规律可循。如果希望反应比较缓和，可以用氯仿或其它卤代烷烃作为稀释剂。反应温度一般都控制在0至20℃。

如果芳环上存在至钝基团，像羧基等，直接氯磺化的温度要提的比较高，要达到100多度。

【Nie, Zhe；etal; J. Med. Chem.; EN; 48; 5; 2005; 1596 - 1609】

反应实例

In a three necked 500 mL round flask equipped withmechanical stirring, was placed with ClSO3H (290 g, 2.49 mol). The system was cooled to 12－15℃ using ice water.  N-Phenyl-acetamide (67.5 g, 0.5 mol) was added dropwise.  The temperature was maintained at 15 oC.  After addition, the reaction mixture washeated at 60oC for two hours. The reaction was cooled down to roomtemperature and poured slowly into 1000 mL of water under finely stirring.  The precipitate was collected by filtration,washed with water, dried to afford desired 4-Acetylamino-benzenesulfonylchloride (90 g, 77% yield).  This sample could be used in next stepwithout further purification.

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