"The reaction of chloro- or bromohydrins with bases provides an economical route for the preparation of epoxides. Halohydrins are readily accessible by treatment of an alkene with either hypochlorous acid (Cl2 + H2O → HOCl), hypochlorite bleach solution (NaOCl), or hypobromous acid (NBS + H2O → HOBr). These reactions involve the initial formation of a halohydrin via anti-addition of X+ and HO-, followed by internal "SN2" displacement of the halide by the oxyanion."