Degradation of alkenes using ozone as an oxidizing agent.

1. OZONOLYSIS
Prepared By
Dr. Krishnaswamy. G
Faculty
DOS & R in Organic Chemistry
Tumkur University
Tumakuru
1

2. Oxidative cleavage of carbon-carbon double bond
using ozone as an oxidizing agent is called Ozonolysis.
The reaction is performed in common organic solvents
such as Dichloromethane (or) Methanol (or) Acetone at
-78o C.
2
R1
R3
R2
R4
R1
R3
R2
R4
O O
O3
Work Up

3. Ozonolysis of carbon-carbon double takes place through
ozonide intermediate followed by work up results in the
formation of respective products.
Work up in the ozonolysis may be divided into three
categories.
3
(1) Reductive work up using mild reducing agents such
as Me2S (or) PPh3 (or) Zn dust.
(2) Reductive work up using strong reducing agents
such as LiAlH4 (or) NaBH4.
(3) Oxidative work up using oxidizing agents such as
H2O2 (or) O2.

4. 4
(1) Reductive work up using mild reducing agents such
as Me2S (or) PPh3 (or) Zn dust produces
aldehyde and ketone.
R1
R3
R2
H
R1
R3
R2
H
O O
O3
Mild Reductive
Work Up
R1
R3
R2
H
O
O O
Me2S/PPh3/
Zn dust
[Ozonide]

5. 5
(2) Reductive work up using strong reducing agents
such as LiAlH4 (or) NaBH4 produces alcohols.
R1
R3
R2
H
R1
R3
R2
OH HO
O3
Strong Reductive
Work Up
R1
R3
R2
H
O
O O
LiAlH4/
NaBH4
[Ozonide]

6. 6
(3) Oxidative work up using oxidizing agents such as
H2O2 (or) O2 provides carboxylic acids.
R1
R3
R2
H
R1
R3
R2
OH
O O
O3
Oxidative
Work Up
R1
R3
R2
H
O
O O
H2O2/
O2
[Ozonide]

7. Ozone inserts to the alkene by 1, 3-dipolar cycloaddition
to form primary ozonide, which is highly unstable and
undergoes retro 1, 3-dipolar cycloaddition to form
carbonyl and carbonyl oxide.
7
R R'
O
R
O
O
Primary Ozonide
O
O
O
O
O
O
R'
O
R
O
O
R'
Carbonyl Carbonyl oxide
1, 3-Dipolar
cycloaddition
Retro 1, 3-Dipolar
cycloaddition
1, 3-dipole
Mechanism

8. 8
Carbonyl oxide which has a dipole undergoes once again
1, 3 – dipolar cycloaddition reaction with carbonyl to for
the stable ozonide.
O
O
O
R'
Carbonyl Carbonyl oxide
R
O
O
O
R R'1, 3-Dipolar
cycloaddition
Ozonide
1, 3-dipole

9. 9
The stable ozonide reacts with reducing (or) oxidizing
agents to give desired products.
O
O
O
R R'
Ozonide
S
Me
Me
O
O
R R'
S
O
MeMe

10. Ozonolysis of simple allenes leads to the formation of
two carbonyl fragments and carbon monoxide.
10
C C C
R1
R3
R2
R4
C O
R1
R3
O C
R2
R4
CO
O3
Ozonolysis of alkynes leads to the formation of either
acid anhydrides or a diketone.
C C
O3
C C
O O
O
C C
O O
C C
O O
O
Diketone Anhydride
Work Up