9.6 Oxidative Cleavage of Alkynes
2 min read•may 7, 2024
Alkynes undergo , breaking their triple bonds to form carbonyl compounds. This process requires powerful like or , and harsh conditions compared to alkene .
The products of oxidation depend on the substituents. yield two ketones, while produce a and an . This reaction showcases the unique reactivity of carbon-carbon triple bonds.
Oxidative Cleavage of Alkynes
Oxidative cleavage of alkynes
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- Breaks carbon-carbon triple bond resulting in formation of two carbonyl compounds (aldehydes or ketones)
- Requires powerful oxidizing agents or harsh reaction conditions compared to alkenes
- Ozone () followed by reductive workup with reducing agents like () or ()
- Potassium permanganate () under acidic conditions
- () in presence of () catalyst
- Mechanism with ozone:
- Ozone adds to alkyne forming unstable intermediate
- Molozonide rearranges to form
- Reductive workup cleaves ozonide yielding two carbonyl compounds
Alkyne vs alkene reactivity
- Alkynes less reactive than alkenes towards oxidative cleavage due to higher bond energy of carbon-carbon triple bond compared to double bond
- Alkenes undergo oxidative cleavage with milder oxidizing agents like () followed by () cleavage
- Products differ:
- Alkynes yield two carbonyl compounds (aldehydes or ketones)
- Alkenes yield two carbonyl compounds or one carboxylic acid and one /aldehyde depending on substitution pattern
Products of alkyne oxidation
- Internal alkynes (R-C≡C-R') yield two ketones
- R and R' groups become or substituents on resulting ketones
- Terminal alkynes (R-C≡C-H) yield carboxylic acid and aldehyde
- R group becomes alkyl or aryl substituent on resulting carboxylic acid
- Hydrogen atom on terminal end oxidized to aldehyde functional group
- Specific products depend on substituents attached:
- Alkyl groups result in aldehydes or ketones with alkyl substituents (methyl, ethyl)
- Aryl groups lead to aldehydes or ketones with aryl substituents (phenyl, naphthyl)
Oxidation and Carbon-Carbon Bond Cleavage
- Oxidation involves the loss of electrons or increase in oxidation state
- occurs as a result of the oxidation process
- Oxidizing agents (e.g., ozone, potassium permanganate) facilitate the reaction
- involves the formation of unstable intermediates leading to bond cleavage
Key Terms to Review (27)
Aldehyde: An aldehyde is a class of organic compounds containing a carbonyl group (C=O) where the carbon atom is bonded to one hydrogen atom and one alkyl or aryl group. Aldehydes are important functional groups in organic chemistry and are involved in various reactions and synthesis pathways.
Alkyl: An alkyl group is a hydrocarbon substituent derived from an alkane by the removal of a single hydrogen atom. Alkyls are commonly found in organic chemistry and are important in the context of various topics, including the oxidative cleavage of alkynes, chemical shifts in 1H NMR spectroscopy, the naming of alcohols and phenols, and the properties of ethers.
Alkyne: An alkyne is a hydrocarbon compound containing a carbon-carbon triple bond. Alkynes are a class of unsaturated organic compounds that play a crucial role in various topics within organic chemistry, including sp hybridization, functional groups, degree of unsaturation, nomenclature, and synthetic transformations.
Aryl: An aryl group is a functional group in organic chemistry that consists of an aromatic ring, typically a benzene ring, bonded directly to another atom or group. Aryl groups are important in the context of oxidative cleavage of alkynes and the properties of ethers.
Arylamine: Arylamines are organic compounds featuring an amine group (NH2) attached to an aromatic ring. These substances play a crucial role in the synthesis of dyes, drugs, and polymers within organic chemistry.
Carbon-Carbon Bond Cleavage: Carbon-carbon bond cleavage refers to the breaking of the covalent bond between two carbon atoms, which is a fundamental process in organic chemistry. This term is particularly relevant in the context of 9.6 Oxidative Cleavage of Alkynes, where carbon-carbon bonds are selectively cleaved through oxidative reactions.
Carboxylic Acid: Carboxylic acids are organic compounds characterized by the presence of a carboxyl functional group (-COOH), which consists of a carbonyl (C=O) and a hydroxyl (-OH) group. They are widely found in nature and play a crucial role in various organic chemistry topics.
Carboxylic acid derivative: Carboxylic acid derivatives are compounds that contain a functional group which is a modified form of the carboxylic acid group (–COOH), where the hydroxyl part (-OH) is replaced by another atom or group of atoms. These derivatives undergo nucleophilic acyl substitution reactions, where an electron-rich nucleophile attacks the carbonyl carbon, leading to the substitution of the leaving group.
Dimethyl Sulfide: Dimethyl sulfide is a colorless, flammable, and volatile organic compound with a strong, unpleasant odor. It is an important chemical species that is commonly encountered in various organic chemistry contexts, including the oxidation of alkenes, the oxidative cleavage of alkynes, and the preparation of aldehydes and ketones.
Internal Alkynes: Internal alkynes, also known as disubstituted alkynes, are a class of organic compounds where the triple bond is positioned between two carbon atoms that are not at the end of the carbon chain. Unlike terminal alkynes, where the triple bond is at the end of the chain, internal alkynes have the triple bond located within the molecule.
Ketone: A ketone is a functional group in organic chemistry that consists of a carbonyl group (a carbon-oxygen double bond) bonded to two alkyl or aryl groups. Ketones are widely encountered in various organic chemistry topics, including the hydration of alkynes, oxidative cleavage of alkynes, organic synthesis, oxidation and reduction reactions, and the chemistry of aldehydes and ketones.
Molozonide: A molozonide is an unstable intermediate formed during the ozonolysis reaction, which is a method of cleaving alkenes and alkynes to produce carbonyl compounds. The molozonide is a key step in the overall mechanism of these oxidative cleavage reactions.
Osmium Tetroxide: Osmium tetroxide is a colorless, volatile, and highly toxic compound with the chemical formula OsO4. It is a powerful oxidizing agent that plays a significant role in various organic chemistry reactions, particularly in the context of the oxidation of alkenes, the cleavage of alkynes, and the preparation of alcohols.
Oxidation: Oxidation is a fundamental chemical process in which a substance loses electrons, resulting in an increase in its oxidation state. This term is central to understanding various reactions and transformations in organic chemistry, from the hydration of alkenes to the oxidation of alcohols and aldehydes.
Oxidative Cleavage: Oxidative cleavage is a chemical reaction that involves the breaking apart of a molecule through the use of an oxidizing agent, resulting in the formation of two or more smaller molecules. This term is particularly relevant in the context of organic chemistry, specifically in the oxidation of alkenes, alkynes, and aldehydes/ketones.
Oxidizing Agents: Oxidizing agents, also known as oxidants, are substances that have the ability to oxidize other substances by removing electrons from them. They play a crucial role in various organic chemistry reactions, including the oxidative cleavage of alkynes, the oxidation of aromatic compounds, the oxidation of alcohols, the preparation of aldehydes and ketones, and the preparation of carboxylic acids.
Ozone: Ozone is a highly reactive allotrope of oxygen that is formed by the interaction of oxygen molecules with ultraviolet radiation. It plays a crucial role in the context of organic chemistry, particularly in the oxidation of alkenes, the cleavage of alkynes, and the preparation of aldehydes and ketones.
Ozonide: An ozonide is a chemical compound formed by the reaction of ozone (O3) with an alkene or alkyne. Ozonides are important intermediates in the oxidative cleavage of carbon-carbon double and triple bonds, leading to the formation of carbonyl compounds.
Periodate: Periodate, also known as sodium periodate or periodic acid, is an oxidizing agent commonly used in organic chemistry for the selective cleavage of alkyne bonds through a process called oxidative cleavage. It is a versatile reagent that finds applications in various organic transformations, particularly in the context of 9.6 Oxidative Cleavage of Alkynes.
Potassium Periodate: Potassium periodate is an inorganic compound with the chemical formula KIO₄. It is a powerful oxidizing agent commonly used in organic chemistry for the oxidative cleavage of alkyne functional groups.
Potassium Permanganate: Potassium permanganate is a strong oxidizing agent with the chemical formula KMnO4. It is a dark purple crystalline solid that is widely used in various chemical reactions and processes due to its powerful oxidizing properties.
Reaction mechanism: A reaction mechanism is a step-by-step sequence of elementary reactions by which overall chemical change occurs. It outlines the specific way in which reactants convert to products, including the formation and breaking of bonds.
Reaction Mechanism: A reaction mechanism is the step-by-step sequence of elementary reactions by which overall chemical change occurs. It describes the detailed pathway that a reaction follows, including the formation and rearrangement of chemical bonds, the generation of intermediates, and the movement of electrons. Understanding reaction mechanisms is crucial for predicting the products of a reaction, explaining reactivity trends, and designing new synthetic pathways.
Ruthenium (II) Chloride: Ruthenium (II) chloride is an inorganic compound with the chemical formula RuCl2. It is a dark green or black crystalline solid that is commonly used as a catalyst in organic chemistry reactions, particularly in the oxidative cleavage of alkynes.
Terminal Alkynes: Terminal alkynes are a class of organic compounds that have a carbon-carbon triple bond at the end of the carbon chain. These unique functional groups are characterized by the presence of a terminal alkyne, which has significant implications in various organic chemistry reactions and transformations.
Zinc: Zinc is an essential mineral that plays a crucial role in various physiological processes within the human body. It is involved in numerous enzymatic reactions and is vital for maintaining proper immune function, protein synthesis, and wound healing.
β Diketone: A β-diketone is an organic compound containing two ketone groups separated by a carbon atom, which is the beta (β) position relative to each ketone group. These molecules are characterized by the presence of hydrogen atoms on the carbon between the two carbonyl (C=O) groups, making them acidic and prone to enolate ion formation.