Welcome to Learn Chemistry by Inam Jazbi!
In this post, we’ll learn about Ozonolysis (or Ozoniation) of Alkenes, also known as the Ozonide Reaction.
This is an important topic in Organic Chemistry (Class 12) where alkenes react with ozone to form ozonides, which later produce aldehydes or ketones.
Let’s understand this reaction step by step in the simplest way possible 👇
Ozonolysis or Ozoniation of Alkenes (Ozonide Reaction)
Definition of Ozonolysis or Ozoniation
The addition of ozone or trioxygen (O3) to an alkene or alkyne to give an adduct called ozonide is known as ozoniation. The hydrolysis of ozonide (product of ozoniation) is called ozonolysis. The process allows for each carbon-carbon double or triple bonds to be replaced by double bonds with oxygen.
In other words,
the
process of preparing the ozonide by the addition
of ozone involving the cleavage of an
alkene or alkyne followed by its subsequent
decomposition by hydrolysis in which the pi bonds between carbon-carbon atoms are broken down in the presence of reducing agent such as zinc or oxidizing agent such as hydrogen peroxide is
called ozonolysis.
Ozonolysis is a chemical reaction involving oxidative cleaving of
the unsaturated bonds of alkenes, alkynes and azo compounds (compounds with the
functional diazenyl functional group) using ozone (O3;
a reactive allotrope of oxygen). It is an organic redox reaction. This reaction
is often used to identify the structure of
unknown alkenes by breaking them
down into smaller, more easily identifiable pieces.
Products
of Ozonolysis or Ozoniation
▶ Oxidation of alkenes with the
help of ozone can give alcohols, aldehydes,
ketones, or carboxylic acids.
The products of ozonolysis are
aldehyde(s) and/or ketone(s), and the exact structures of the products depend
on the structure of the initial alkene:
Disubstituted alkene carbons are
oxidatively cleaved to ketone.
Monosubstituted alkene carbons
are oxidatively cleaved to aldehyde.
Unsubstituted alkene carbons are
oxidatively cleaved to formaldehyde (HCHO).
▶ Alkynes undergo ozonolysis to
give acid anhydrides or diketones. If
water is present in the reaction, the acid anhydride undergoes
hydrolysis to yield two carboxylic acids.
For external alkynes, the ozonolysis results in a carboxylic acid and
carbon dioxide: The ozonolysis of internal alkynes, on the other hand,
produces two carboxylic acids.
Alkynes are less reactive than alkenes towards O3.
▶ For azo compounds, the ozonolysis
yields nitrosamines.
Once the ozone is added to the
reaction mixture, a reagent must be added to convert the ozonide to the
required carbonyl derivative. For this conversion, 2
techniques can be employed:
▶ Reductive
Workup
▶ Oxidative
Workup
However, reductive workup
conditions seen a lot more in use when compared to oxidative workup conditions.
In these workup conditions, triphenylphosphine, thiourea, zinc dust, and
dimethyl sulfide can be used to produce aldehydes or ketones. On the other hand,
hydrogen peroxide can be used to produce carboxylic acids.
The ozonolysis of an alkene involves
addition of ozone in the presence of ether
which initially gives an ozonide intermediate which are unstable
undergoes decomposition (either with
Zn or H2O2) to form carbonyl
compounds (an aldehyde or ketone or both). The ozonolysis of
Alkenes with ozone (O3) involves oxidative
cleavage giving carbonyl compounds, cleaving the C=C bond
The reaction generates an ozonide intermediate,
which is then treated with a reducing agent (e.g. dimethyl sulfide or zinc)
gives aldehydes or ketones depending on the structure of the starting alkene.
One of the advantages of ozonolysis compared to other
oxidative cleavage reactions is that it does not over-oxidize the alkene
to carboxylic acid unlike, for example, the potassium permanganate (KMnO4):
General Reaction
Formaldehyde is formed when ozonide is treated with a reducing agent
like zinc dust in the presence of boiling water.
Complete Reaction
Application
Ozonolysis is used to detect the position of double bond.
#ChemistryNotes #Class12Chemistry #OrganicChemistry #Ozonolysis #Ozoniation #OzonideReaction #LearnChemistry #InamJazbi
This content is for subscribed members only
Enter the password provided after subscription to unlock this post.
If you haven't subscribed yet, please visit our Subscription page for payment details.