Oxymercuration-Demercuration A Special Electrophilic Addition

The last example in Table 12-2 is an electrophilic addition of a mercuric salt to an alkene. The reaction is called mercuration, and the resulting compound is an alkyl-mercury derivative, from which the mercury can be removed in a subsequent step. One particularly useful reaction sequence is oxymercuration-demercuration, in which mercuric acetate acts as the reagent. In the first step (oxymercuration), treatment of an alkene with this species in the presence of water leads to the corresponding addition product. 

In the subsequent demercuration, the mercury-containing substituent is replaced by hydrogen through treatment with sodium borohydride in base. The net result is hydration of the 

The alcohol obtained after demercuration is the same as the product of Markovnikov hydration (Section 12-4) of the starting material. However, oxymercuration-demercuration is a valuable alternative to acid-catalyzed hydration, because no carbocation is involved therefore oxymercuration-demercuration is not susceptible to the rearrangements that commonly occur under acidic conditions (Section 12-3). Its use is limited by the expense of the mercury reagent and its toxicity, which requires careful removal of mercury from the product and safe disposal. 

REAL LIFE MEDICINE 12-1 Juvenile Hormone Analogs in the Battle Against 

Juvenile hormone (JH) is a substance that controls metamorphosis in insects. It is produced by the male wild silk moth, Hyalophora cecropia L., and its presence delays the maturation of insect larvae until the appropriate 

---