Name: alkene bond cutting by ozonolysis
Uploaded: 2023-04-30T18:28:37.000Z
Duration: 1 min 46 s
Channel: JoVE

Ozonolysis of alkenes is an oxidative cleavage reaction where the carbon&#8211;carbon double bond cleaves completely to form two carbon&#8211;oxygen bonds.
The reaction proceeds with the addition of ozone to alkenes followed by reduction in the presence of mild reducing agents, such as dimethyl sulfide or zinc dust in water, to form corresponding aldehydes and ketones.
Ozone is a colorless gas generated by passing oxygen through an electric discharge. It is a symmetrical bent molecule that exists as a resonance hybrid of two contributing Lewis structures.
The first step of the mechanism involves an electrophilic addition of ozone across the alkene double bond, forming a molozonide, which splits into a carbonyl oxide and a carbonyl compound. Next, the intermediates rearrange to form a relatively stable ozonide.
In the second step, a mild reducing agent such as dimethyl sulfide converts the ozonide into carbonyl compounds.
Ozonolysis of alkenes yields different products based on the structure of the starting alkene and the reaction conditions.
For example, ozonolysis of a monosubstituted alkene such as 1-butene followed by a reductive workup with dimethyl sulfide yields a mixture of aldehydes. A trisubstituted alkene such as 2-methyl-2-butene forms an aldehyde and a ketone.
However, an oxidative workup using hydrogen peroxide further oxidizes the aldehydes to carboxylic acids while the ketones remain intact.

oxidative cleavage of alkenes: ozonolysis

Oxidative Cleavage of Alkenes: Ozonolysis

In ozonolysis, ozone is used to cleave a carbon&#8211;carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
<img alt="Resonance structure of ozone molecule diagram; electron movement, chemical bonding concept." src="/files/ftp_upload/11784/11784_PT_Figure_1.svg" style="text-align: center; height: 65px;" data-altupdatedat="1761830439000" data-alt="Figure1" />
Ozonolysis proceeds through an oxidative cleavage reaction. The first step is the electrophilic addition of ozone across the alkene double bond, forming an unstable molozonide intermediate, which reacts further to form a carbonyl and a carbonyl oxide. These intermediates rearrange to form an ozonide.
<img alt="Chemical reaction mechanism diagram, illustrating bond rearrangement and reaction intermediates." src="/files/ftp_upload/11784/11784_PT_Figure_2.svg" style="text-align: center; height: 225px;" data-altupdatedat="1761830439000" data-alt="Figure2" />
The ozonide is treated with a mild reducing agent such as dimethyl sulfide or zinc to yield the carbonyl compounds as the final product.
<img alt="Organic reaction diagram, Baeyer-Villiger oxidation process, carbonyl insertion method." src="/files/ftp_upload/11784/11784_PT_Figure_3.svg" style="text-align: center; height: 65px;" data-altupdatedat="1761830439000" data-alt="Figure3" />
<h4>Ozonolysis with Different Substituted Alkenes</h4>
The conversion of ozonide to aldehydes, ketones, or carboxylic acids depends on the structure of the alkene starting material and different reaction conditions.
When a reductive work-up is used, ozonolysis of monosubstituted alkenes such as 1-butene yields a mixture of aldehydes.
<img alt="Ozonolysis reaction diagram: Alkene cleavage forming aldehydes; O&#8323;, (CH&#8323;)&#8322;S process." src="/files/ftp_upload/11784/11784_PT_Figure_4.svg" style="text-align: center; height: 65px;" data-altupdatedat="1761830439000" data-alt="Figure4" />
Trisubstituted alkenes, such as 2-methyl-2-butene, on the other hand, form an aldehyde and a ketone.
<img alt="Ozonolysis reaction diagram, alkene conversion to carbonyl compounds using O&#8323;, CH&#8323;)&#8322;S method." src="/files/ftp_upload/11784/11784_PT_Figure_5.svg" style="text-align: center; height: 65px;" data-altupdatedat="1761830439000" data-alt="Figure5" />
When an oxidative work-up is used, the reaction yields a ketone and an aldehyde that is further oxidized to the corresponding carboxylic acid.
<img alt="Ozonolysis reaction diagram for alkene oxidation; chemical equation with ozone and hydrogen peroxide." src="/files/ftp_upload/11784/11784_PT_Figure_6.svg" style="text-align: center; height: 65px;" data-altupdatedat="1761830439000" data-alt="Figure6" />

In ozonolysis, ozone is used to cleave a carbon&#8211;carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
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Education

JoVE Core

Organic Chemistry

Unit 1

Reactions of Alkenes

KEY TERMS AND CONCEPTS

alkene bond cutting by ozonolysis

Ozonolysis is a reaction that cuts a carbon-carbon double bond in an alkene. Ozone attacks the double bond and breaks the molecule into smaller carbonyl products. Depending on the work-up, the products can be aldehydes, ketones, or carboxylic acids.

Ozone is a symmetrical bent molecule with a resonance-stabilized structure. The reaction starts with electrophilic addition of ozone across the alkene double bond. This step forms an unstable molozonide, which then reacts further to give a carbonyl compound and a carbonyl oxide.

These intermediates rearrange to form an ozonide. The ozonide is then treated with a mild reducing agent, such as dimethyl sulfide or zinc, to produce the final carbonyl compounds. This reductive work-up is the step that controls which products are isolated from the reaction.

The product mix also depends on the alkene starting material. With a reductive work-up, monosubstituted alkenes such as 1-butene give a mixture of aldehydes. Trisubstituted alkenes, such as 2-methyl-2-butene, form an aldehyde and a ketone.

An oxidative work-up changes the outcome. In that case, the reaction gives a ketone and an aldehyde that is further oxidized to the corresponding carboxylic acid. This makes ozonolysis a useful way to map an alkene into smaller oxygen-containing molecules.

Alkene Bond Cutting by Ozonolysis

regioselectivity of electrophilic additions-peroxide effect

regioselectivity-of-electrophilic-additions-peroxide-effect

Peroxide Effect in HBr Alkene Addition

Hydrogen bromide can add to an alkene in a way that goes against Markovnikov’s rule when organic peroxides are present. For example, 2-methylpropene reacts with HBr and peroxide to give 1-bromo-2-methylpropane. This change in product comes from a free radical mechanism, which reverses the usual regioselectivity. The reaction has three stages: initiation, propagation, and termination. In initiation, an oxygen-oxygen bond in the radical initiator breaks by homolytic cleavage, meaning each atom...

free-radical chain reaction and polymerization of alkenes

free-radical-chain-reaction-and-polymerization-of-alkenes

How Alkene Monomers Form Polymers

Alkene monomers can join together to form polymers, which are large macromolecules used in many commercial products. In a polymer, the repeating unit defines the structure, while the terminal groups are considered insignificant. The average degree of polymerization shows how many repeating units are in a polymer molecule and is written as the subscript n. Alkenes form polymers through a free-radical chain reaction with three main stages: initiation, propagation, and termination. In the...

halogenation of alkenes

Anti Addition in Alkene Halogenation

Halogenation of alkenes adds chlorine or bromine across a carbon-carbon double bond to form a vicinal dihalide. This reaction is carried out in inert, non-nucleophilic solvents such as methylene chloride, chloroform, or carbon tetrachloride. The reaction starts when bromine is drawn toward the pi electrons of an alkene such as cyclopentene. One bromine atom acts as an electrophile and adds across the double bond. This forms a cyclic bromonium ion intermediate. The bromonium ion is more stable...

formation of halohydrin from alkenes

Bromohydrin Addition in Alkene Reactions

Bromohydrin addition shows how an alkene can react with bromine in water to form a halohydrin. In this reaction, the product has a halogen and a hydroxyl group on neighboring carbons. When the halogen is bromine, the product is called a bromohydrin. When the halogen is chlorine, it is called a chlorohydrin. The reaction begins when the pi electrons of the alkene react with electrophilic bromine. This step forms a bridged intermediate called a bromonium ion. Water then acts as a nucleophile. It...

acid-catalyzed hydration of alkenes

Hydrating Alkenes to Form Alcohols

Alkenes can be converted into alcohols by adding water in the presence of an acid. Without acid, this hydration happens too slowly to matter in practice. The acid is not used up in the reaction, so this is an acid-catalyzed process. Strong acids such as sulfuric acid dissociate completely in water. In that case, the reacting acid species is the hydronium ion. The first step is a slow protonation of the alkene at the less-substituted end. This forms the more-substituted carbocation, which is...

regioselectivity and stereochemistry of acid-catalyzed hydration

regioselectivity-and-stereochemistry-of-acid-catalyzed-hydration

Carbocation Stability in Alkene Hydration

Acid-catalyzed hydration of alkenes forms alcohols through a carbocation intermediate. The reaction starts when hydronium ion protonates the alkene. This step is slow and controls the overall rate. The alkene structure matters because alkyl substituents at the double bond can change how fast the reaction occurs. The kind of carbocation formed also affects the rate. A reaction that passes through a tertiary carbocation is faster than one that forms a secondary or primary carbocation. This is...

oxymercuration-reduction of alkenes

Markovnikov Hydration with Mercury

Oxymercuration-reduction is a way to turn an alkene into an alcohol. It hydrates the alkene using mercuric acetate in a mix of tetrahydrofuran and water. The reaction first makes an organomercury adduct and then reduces it to an alcohol with sodium borohydride. The solvent mix has two jobs. Tetrahydrofuran dissolves the alkene and the aqueous mercuric acetate solution. Water acts as both a reactant and a solvent for mercuric acetate. The mechanism can be seen in the conversion of...

hydroboration-oxidation of alkenes

Anti-Markovnikov Alcohols from Alkenes

Hydroboration-oxidation turns alkenes into alcohols with anti-Markovnikov orientation. It is a complementary route to oxymercuration-demercuration, which gives Markovnikov products. In this reaction, borane adds across the alkene first, and basic hydrogen peroxide finishes the conversion to an alcohol. Borane is very reactive because the boron atom has only six electrons in its valence shell. It also has an empty 2p orbital that sits perpendicular to the plane formed by boron and its three...

regioselectivity and stereochemistry of hydroboration

regioselectivity-and-stereochemistry-of-hydroboration

Hydroboration Reaction Paths and Product Control

Hydroboration shows how alkene reactions control both where atoms add and how the product is shaped. In hydroboration–oxidation, borane attacks the alkene π bond in a concerted way, which means the bond changes happen together. This forms a cyclic, four-centered transition state. In this transition state, the BH2 group attaches to the less substituted carbon, while H attaches to the more substituted carbon. The addition happens across the same face of the alkene, so the reaction gives syn...

oxidation of alkenes: syn dihydroxylation with osmium tetraoxide

oxidation-of-alkenes-syn-dihydroxylation-with-osmium-tetraoxide

Alkene Dihydroxylation with Osmium Tetroxide

Alkene dihydroxylation with osmium tetroxide adds two hydroxyl groups across a double bond to make 1,2-diols, also called glycols. The reaction can give either anti or syn products, and this method follows syn stereochemistry. That means both new O atoms add to the same face of the alkene. The reaction occurs in two steps. First, osmium tetroxide adds to the alkene double bond in a concerted step, where both bonds form at the same time. This creates a five-membered cyclic osmate ester...

oxidation of alkenes: syn dihydroxylation with potassium permanganate

oxidation-of-alkenes-syn-dihydroxylation-with-potassium-permanganate

Potassium Permanganate Tests for Alkene Bonds

Potassium permanganate can be used to test and change alkene double bonds. When an alkene reacts with cold, dilute potassium permanganate under basic conditions, it forms a cis-diol, which is a molecule with two hydroxyl groups on the same side. A brown precipitate of manganese dioxide also appears during the reaction. The reaction starts when the permanganate ion adds to the same side of the alkene pi bond. This syn addition forms a cyclic manganate ester intermediate. Water then hydrolyzes...

oxidation of alkenes: anti dihydroxylation with peroxy acids

oxidation-of-alkenes-anti-dihydroxylation-with-peroxy-acids

Epoxide Route to Trans Diols

Epoxides provide a route to trans diols from alkenes. In anti dihydroxylation, an alkene is treated with a peroxycarboxylic acid to first make an epoxide. A diol is a compound with two hydroxyl groups, and in this pathway the two OH groups end up on opposite sides. An epoxide is a highly strained three-membered ring. Oxygen and two carbon atoms sit at the corners of an equilateral triangle. The first step uses a peracid, which is a strong oxidizing agent related to a carboxylic acid but with...

Ozonolysis is a reaction that cuts a carbon-carbon double bond in an alkene. Ozone attacks the double bond and breaks the molecule into smaller carbonyl products. Depending on the work-up, the products can be aldehydes, ketones, or carboxylic acids. Ozone is a symmetrical bent molecule with a resonance-stabilized structure. The reaction starts with electrophilic addition of ozone across the alkene double bond. This step forms an unstable molozonide, which then reacts further to give a carbonyl...

reduction of alkenes: catalytic hydrogenation

reduction-of-alkenes-catalytic-hydrogenation

Alkene Hydrogenation and Alkane Stability

Alkene hydrogenation turns an alkene into an alkane by adding molecular hydrogen. This reduction usually happens with a transition-metal catalyst, so the reaction is called catalytic hydrogenation. Palladium, platinum, and nickel are common catalysts in solid form as fine powder on an inert surface. These catalysts do not dissolve in the reaction mixture, so they are heterogeneous catalysts. The reaction takes place on the metal surface. First, hydrogen adsorbs onto the surface and the H-H...

reduction of alkenes: asymmetric catalytic hydrogenation

reduction-of-alkenes-asymmetric-catalytic-hydrogenation

Chiral Alkene Hydrogenation for Drug Synthesis

Catalytic hydrogenation adds molecular hydrogen to an alkene double bond and turns it into an alkane. A transition-metal catalyst drives the reaction, and the hydrogen atoms add in syn stereochemistry, meaning they enter from the same side. The catalyst can be heterogeneous or homogeneous. When hydrogenation creates a chiral center, the products are usually a pair of enantiomers, which are mirror-image molecules. An enantiomeric excess of one product can be obtained with an enantioselective...

key terms and concepts

Learn how ozonolysis breaks alkene double bonds and forms aldehydes, ketones, or carboxylic acids based on the work-up and starting alkene.

Alkene Bond Cutting by Ozonolysis | JoVE K12

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Alkene Bond Cutting by Ozonolysis

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