次卤酸对烯烃的加成，生成邻卤醇，其反应本质及选择性相同与卤素加成反应。卤素正离子首先对烯烃的双键作亲电进攻，生成桥卤三元环过渡态，然后，水分子或羟基对其亲核进攻，得到邻卤醇。按照马氏规则，卤素加成在双键的取代基较少的一端。

应用次卤酸酯（ROX）作为卤化剂，其机理相同于次卤酸的反映，但是可在非水溶液中进行反应。根据溶剂的亲核基团不同，可生成相应的-卤醇β衍生物。

反应实例

Under vigorous agitation andcooling to 0.deg.-5.deg. C., 150 g of chlorine is introduced within 6 hoursinto a solution of 182 g of cis-1,4-dihydroxy-2-butene and 288 g ofcrystallized soda (Na2CO3 *10H2O).. The mixture is stirred for another hour,concentrated under vacuum at 50.deg.-55.deg. C., and diluted with 0.6 l ofethanol.. After standing overnight, the mixture is filtered off from sodiumchloride and thoroughly washed with ethanol. The solution and the filtrate areconcentrated, thus obtaining 3-chloro-1,2,4-butanetriol as a yellow oil. Yield:272 g (97percent of theory) of 3-chloro-1,2,4-butanetriol.

【Patent; SheringAktiengesellschaft; Publ.: US4570007 A1 (1986/02/11), Appl.: US1985-722088(1985/04/11).】

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