Advices For Studying Organic Chemistry

11.5 ALCOHOLS FROM ALKENES THROUGH

OXYMERCURATION-DEMERCURATION

1. Alkenes react with Hg(OAc) 2 in a mixture of THF and water to produce
   (hydroxyalkyl)mercury compounds.


2. The (hydroxyalkyl)mercury compounds can be reduced to alcohols with NaBH 4.
   Step 1: Oxymercuration

CC H 2 O THF CC

OHHg

H

OCCH 3

CCH 3

O

CH 3 CO

O

++HgO 2 O +

Step 2: Demercuration

OH−+ NaBH 4 CC

OH OHH

CC + + Hg +

Hg

CH 3 CO−

O

OCCH 3

O

3. Both steps can be carried out in the same vessel, and both reactions take place
   very rapidly at room temperature or below.

1. Oxymercuration usually goes to completion within a period of 20 s to 10 min.


2. Demercuration normally requires less than an hour.


3. The overall reaction gives alcohols in very high yields, usually greater than 90%.

4. Oxymercuration-demercuration is highly regioselective.
   
   
   1. The H– becomes attached to the carbon atom of the double with the greater
      number of hydrogen atoms:
   
   
   
   

CC

R

H

H

H

HO

OH

H 2 O

H

R C C

H

H

H

+ H

1. Hg(OAc) 2 /THF-
   2. NaBH 4 , OH−