This ppt was made to describe the reagent named Osmium tetroxide which is used to produce diols.

1. Osmium Tetroxide
(OsO4)

2. Osmium Tetroxide:
 Oxidising agent.
 Toxic, Volatile and Expense
 Osmium in OsO4 is in +8 Oxidation state.
 Extremely electron deficient.
 Dihydroxylation of Alkenes gives 1,2-diol products.
 Osmium(VI) species can be oxidized or reduced and hydrolyses to
release the diol product.
 Accelerated by tertiary amines and other bases, such as pyridine.

3. Dihydroxylation:
Osmate ester Diol
Alkene
a glycol
(90 – 95 % yield)
1.
2.

4. Mechanism:
high oxidation
state, accepts
electrons
Cyclic osmate
ester
reduced to +6
oxidation
state
Hydrolysed to
form glycol
1.
2.

5. Recycle of OsO4
Common
Oxidants used to
recycle OsO4
N-methylmorpholine-N-oxide
(NMO)
trimethylamine-N-oxide
(TMAO)
tert-butyl
hydroperoxide
Potassium
ferricyanide
+
cyclohexene NMO cis-1,2-cyclohexanediol
(89% yield)

6. 2,3-dimethyl-2-butene
TMAO
2,3-dimethyl-2,3-
butanediol (85% yield)

7. Syn dihydroxylation