Ozonolysis: History, Types, and Examples

Ozonolysis is a chemical reaction in which ozone is employed. However, it cleaves the double bond and triple bond of alkenes and alkynes respectively. It results in the formation of carbonyl compounds. This reaction is used for the identification of the structure of alkenes.

What is ozonolysis?

The ozone (O3), is a triatomic form of oxygen. It can be represented by the two most stable lewis structures.

“When ozone reacts with an alkene to form ozonide by breaking the double bond is known as ozonolysis.”

Alkynes can also undergo ozonolysis to give acid anhydride and diketones.

History of ozonolysis

Christian Friedrick Schonbein discovered ozone in 1840. He also did ozonolysis in 1845. However, he observed that after the reaction of ethylene with ozone, the smell of ozone and ethylene was not perceivable. Although the ozonolysis of alkene is also referred to as “Harries ozonolysis”. This is because there are some attributes of this reaction to Carl Dietrich Harries.

Types of ozonolysis

There are two types of ozonolysis.

Reductive ozonolysis

“The addition of ozone followed by hydrolysis in the presence of reducing agent is known as reductive ozonolysis.”

This mainly happens in the case of alkenes.

Oxidative ozonolysis

“The addition of ozone followed by the hydrolysis in the absence of reducing g agents is known as oxidative ozonolysis.”

However, this mainly happens in the case of alkynes.

Examples

Ozonolysis of alkenes

Alkenes undergo ozonolysis to form aldehyde, alcohols, ketone, and carboxylic acid. The formation of the product depends on the structure of the alkene.

Mechanism

Step 1

The reaction begins by passing g the ozone-containing air through a solution of an alkene. This is done in the presence of an inert solvent such as chloroform. Thus, the temperature is maintained at about -80℃. The initially formed product molozonide rearrange into ozonide. 

Step 2

The ozonide is highly unstable. Therefore, they are decomposed into cleavage products by hydrolysis. In this way, the double-bonded carbon in the alkene changed into the double bond to oxygen.

The byproduct hydrogen peroxide may oxidize aldehyde or ketone into the carboxylic acid. Therefore, the decomposition of ozonide is done under reduction conditions. For example, zinc dust in a dilute acid is used.

Ozonolysis of alkynes

When alkynes react with ozone the carboxylic acids are produced. Some examples are given below:

This reaction is used in the structure determination of the alkynes. However, by identifying the structure of carboxylic acid, we can determine the structure of alkyne.

Mechanism

Step 1 

In the first step, ozone is added to the alkynes. This results in the formation of ozonide. Which on hydrolysis gives 1,2 dicarbonyl compounds.

Step 2

The byproduct hydrogen peroxide affects the oxidative cleavage of carbonyl compounds forming the mixture of carboxylic acid.

Ozonolysis of benzene

The benzene reacts with ozone and produces three molecules of glyoxal through the formation of triozonide. Hence, this reaction provides the existence of three double bonds in benzene.


However, the ozonolysis of alkyl benzene in the presence of hydrogen peroxide yield aliphatic carboxylic acid.

Applications

Ozonolysis is used to locate the position of the double bond. However, it can also determine the position of the triple bond. It is also used in determining the structure of natural products. For example terpenes.

Concepts Berg

How many types of ozonolysis are there?

There are two different types of ozonolysis.

  • Reductive ozonolysis
  • Oxidative ozonolysis

What does O3 do in reaction?

The ozone is used for the cleavage of the double bond of alkenes. However, it is also used for the cleavage of the triple bond of alkynes. In this way, carbonyl compounds such as aldehyde, ketone, and carboxylic acid are produced.

What is the application of ozonolysis?

It is mainly used for the identification of the position of double bonds and triple bonds.

What is the mechanism of ozonolysis of propylene?

The mechanism of ozonolysis of propylene is shown below:

Can Ozonolysis of an internal alkyne ever produce aldehydes?

The ozonolysis of terminal alkynes produces dicarboxylic acid. Which undergo oxidative cleavage and produce a mixture of carboxylic acid.

Reference Books 

  • Organic Reactions Mechanism with Problems by Dr. Rajpal Tyagi (M.M.H Post Graduate College Ghaziabad)
  • A textbook of Organic Chemistry by M. Younas (University of Punjab)

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