9.5 Reduction of Alkynes

Sodium in liquid ammonia refers to the reaction that occurs when metallic sodium is dissolved in liquid ammonia, forming a deep blue solution with unique chemical properties. This reaction is particularly relevant in the context of the reduction of alkynes, as it can be used as a reducing agent in organic chemistry.

Solvated Electron: A solvated electron is an electron that is dissolved in a solvent, such as liquid ammonia, forming a highly reactive species that can act as a powerful reducing agent.

Reductive Amination: Reductive amination is a chemical reaction where an aldehyde or ketone is reduced and simultaneously combined with an amine, forming a new amine product.

Dissolving Metal Reduction: Dissolving metal reduction is a type of reduction reaction where a metal, such as sodium, is dissolved in a solvent like liquid ammonia, creating a reducing environment for organic compounds.

Hydrogenation is a chemical reaction in which hydrogen gas (H2) is added to an organic compound, typically an alkene or alkyne, to produce a more saturated compound. This process is commonly used in the food industry to convert unsaturated fats into more stable, saturated fats.

Alkene: An unsaturated hydrocarbon containing at least one carbon-carbon double bond.

Alkyne: An unsaturated hydrocarbon containing at least one carbon-carbon triple bond.

Catalytic Hydrogenation: A hydrogenation reaction that uses a catalyst, such as platinum or palladium, to speed up the process and improve efficiency.

Palladium on carbon, often abbreviated as Pd/C, is a heterogeneous catalyst commonly used in organic chemistry for the selective reduction of alkynes to alkenes. It consists of palladium metal dispersed on a porous carbon support, which provides a high surface area for the catalytic reaction to occur.

Heterogeneous Catalyst: A catalyst that exists in a different phase (solid) from the reactants (liquid or gas), allowing for easy separation and reuse of the catalyst.

Alkyne Reduction: The process of selectively reducing a carbon-carbon triple bond (alkyne) to a carbon-carbon double bond (alkene) using hydrogen gas and a catalyst.

Hydrogenation: A chemical reaction where hydrogen is added to a compound, typically to reduce or saturate carbon-carbon multiple bonds.

Pd/C, or palladium on carbon, is a heterogeneous catalyst commonly used in organic chemistry reactions, particularly in the reduction of alkynes and the synthesis of amines. It consists of palladium metal dispersed on a porous carbon support, which enhances the catalytic activity and stability of the palladium.

Heterogeneous Catalyst: A catalyst that exists in a different phase (solid) than the reactants (liquid or gas), allowing for easier separation and reuse of the catalyst.

Hydrogenation: A chemical reaction where hydrogen is added to a compound, typically used to reduce unsaturated bonds such as alkenes and alkynes.

Reductive Amination: A two-step reaction where an aldehyde or ketone is first converted to an imine, which is then reduced to form a secondary amine.

A Lindlar catalyst is a specially prepared palladium on calcium carbonate (Pd/CaCO3) that is poisoned with lead acetate and quinoline. It is used in organic chemistry to selectively hydrogenate alkynes to cis-alkenes, without reducing them further to alkanes.

Alkyne: Hydrocarbons containing at least one carbon-carbon triple bond, serving as the starting material for reduction reactions.

Hydrogenation: The chemical reaction that involves the addition of hydrogen (H2), typically to unsaturated organic compounds such as alkenes and alkynes.

Cis: Alkene - An alkene where the hydrogen atoms are positioned on the same side of the double bond, often resulting from selective hydrogenation processes like those using a Lindlar catalyst

Quinoline is a heterocyclic aromatic compound consisting of a benzene ring fused to a pyridine ring. It is an important structural motif found in various natural and synthetic compounds, with applications in organic chemistry, medicinal chemistry, and materials science.

Heterocyclic Compound: A cyclic compound that contains atoms of at least two different elements as members of its ring structure, typically including nitrogen, oxygen, or sulfur.

Aromatic Compound: A cyclic compound that exhibits aromatic character, typically due to the presence of a conjugated pi system that confers enhanced stability.

Pyridine: A basic heterocyclic aromatic compound containing a single nitrogen atom in a six-membered ring.

Catalytic poisoning refers to the deactivation or reduction in the efficiency of a catalyst due to the presence of certain substances that interfere with the catalyst's active sites or alter its chemical properties. This phenomenon is particularly relevant in the context of the reduction of alkynes, where the catalyst plays a crucial role in the reaction.

Catalyst: A substance that increases the rate of a chemical reaction without being consumed or altered itself.

Active Site: The specific region on a catalyst where the reactants bind and the chemical transformation takes place.

Catalyst Deactivation: The process by which a catalyst loses its effectiveness, often due to poisoning or fouling.

Dissolving metal reduction, also known as metal-ammonia reduction, is a type of chemical reaction where a metal, typically an alkali metal like sodium or lithium, is dissolved in liquid ammonia to form a reducing agent. This reducing agent can then be used to selectively reduce certain functional groups, such as alkynes or nitro groups, in organic synthesis.

Alkali Metals: The group of highly reactive metals in the periodic table, including lithium, sodium, potassium, rubidium, cesium, and francium.

Solvated Electron: An electron that is dissolved in a solvent, such as liquid ammonia, and behaves as a reducing agent in chemical reactions.

Reductive Amination: A two-step process in organic synthesis where a carbonyl compound is first converted to an imine, then reduced to a secondary amine.

A Lindlar catalyst is a specially prepared palladium on calcium carbonate (Pd/CaCO3) that is poisoned with lead acetate and quinoline. It is used in organic chemistry to selectively hydrogenate alkynes to cis-alkenes, without reducing them further to alkanes.

Alkyne: Hydrocarbons containing at least one carbon-carbon triple bond, serving as the starting material for reduction reactions.

Hydrogenation: The chemical reaction that involves the addition of hydrogen (H2), typically to unsaturated organic compounds such as alkenes and alkynes.

Cis: Alkene - An alkene where the hydrogen atoms are positioned on the same side of the double bond, often resulting from selective hydrogenation processes like those using a Lindlar catalyst

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.

sp Hybridization: The process by which an atom's atomic orbitals mix to form new hybrid orbitals, allowing for the formation of a carbon-carbon triple bond in alkynes.

Unsaturated Compounds: Organic compounds that contain one or more carbon-carbon multiple bonds, such as the triple bond found in alkynes, resulting in a higher degree of unsaturation.

Organic Synthesis: The design and construction of complex organic molecules, often involving the use of alkynes as key intermediates or building blocks.

A radical anion is a species that contains an unpaired electron and a negative charge. These reactive intermediates are important in various organic chemistry reactions, including the reduction of alkynes and the formation of Grignard reagents.

Radical: A species with an unpaired electron, which makes it highly reactive and unstable.

Anion: A negatively charged ion that results from the gain of one or more electrons by an atom or molecule.

Reducing Agent: A substance that donates electrons, causing another substance to be reduced (gain electrons).

A vinyl radical is a reactive organic species containing an unpaired electron on a carbon atom that is part of a carbon-carbon double bond. It is an important intermediate in various chemical reactions, particularly in the context of alkyne reduction.

Radical: A radical is a highly reactive species containing an unpaired electron, which makes it prone to participating in addition and substitution reactions.

Alkyne: An alkyne is a hydrocarbon containing a carbon-carbon triple bond, which can undergo various reactions, including reduction to form alkenes or alkanes.

Hydrogenation: Hydrogenation is a chemical reaction in which hydrogen is added to a compound, typically to reduce a carbon-carbon multiple bond.

A vinyl anion is a negatively charged carbon-based species with a double bond and a lone pair of electrons on the same carbon atom. These reactive intermediates are important in various organic chemistry reactions, particularly in the context of alkyne reduction.

Nucleophile: A nucleophile is a species that donates a pair of electrons to form a new covalent bond, often with an electrophilic carbon atom.

Hydrogenation: Hydrogenation is a chemical reaction that adds hydrogen to a compound, typically reducing a multiple bond (e.g., alkene or alkyne) to a single bond.

Reductive Elimination: Reductive elimination is a reaction in which two substituents are removed from a metal center, forming a new covalent bond between them.

A trans-alkene is a type of alkene, or carbon-carbon double bond, where the two largest substituents are positioned on opposite sides of the double bond. This geometric arrangement contrasts with cis-alkenes, where the largest substituents are on the same side of the double bond.

Cis-Alkene: A cis-alkene is an alkene where the two largest substituents are positioned on the same side of the carbon-carbon double bond.

Alkyne: An alkyne is a hydrocarbon containing a carbon-carbon triple bond.

Reduction: Reduction is a chemical reaction that adds hydrogen atoms or removes oxygen atoms, resulting in a decrease in oxidation state.

Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules and how this arrangement affects the chemical and physical properties of the substance. It examines the spatial orientation of atoms and their relationship to one another, which is crucial in understanding many organic chemistry concepts.

Chirality: The property of a molecule that makes it non-superimposable on its mirror image, resulting in the existence of enantiomers.

Enantiomers: A pair of molecules that are non-superimposable mirror images of each other, having the same chemical formula and connectivity but different spatial arrangements.

Cis-Trans Isomerism: The phenomenon where two substituents on a double bond or a ring can be on the same side (cis) or opposite sides (trans) of the molecule, resulting in different spatial arrangements.

Metal hydrides are chemical compounds formed by the combination of a metal and hydrogen. They are important in the context of the reduction of alkynes, as they can be used as reducing agents to selectively convert triple bonds to single bonds.

Reducing Agent: A reducing agent is a substance that has the ability to reduce other substances by donating electrons, thereby lowering their oxidation state.

Alkyne Reduction: The process of selectively converting a triple carbon-carbon bond (alkyne) to a single carbon-carbon bond (alkane) using a reducing agent.

Hydrogenation: The addition of hydrogen to a compound, often used to reduce unsaturated bonds such as alkenes and alkynes.

Reaction kinetics is the study of the rates and mechanisms of chemical reactions. It examines the factors that influence the speed and efficiency of a reaction, such as temperature, pressure, and the presence of catalysts. This concept is crucial in understanding organic reactions, as the rate and pathway of a reaction can have a significant impact on the products formed and the overall efficiency of the process.

Reaction Rate: The rate at which reactants are converted into products, typically measured as the change in concentration of reactants or products over time.

Activation Energy: The minimum energy required to initiate a chemical reaction, which must be overcome for the reaction to occur.

Transition State: The high-energy, unstable intermediate state that reactants must pass through in order to form products.

Alkyne reduction is the process of converting a carbon-carbon triple bond (an alkyne) into a carbon-carbon single bond (an alkane) through the addition of hydrogen atoms. This reaction is an important transformation in organic chemistry that can be used to selectively modify the structure and reactivity of organic compounds.

Hydrogenation: The process of adding hydrogen to a compound, typically to reduce a multiple bond such as an alkene or alkyne.

Catalytic Reduction: A reduction reaction that is facilitated by the presence of a catalyst, which can improve the rate, selectivity, and efficiency of the transformation.

Lindlar Catalyst: A heterogeneous catalyst used for the partial hydrogenation of alkynes to produce alkenes, composed of palladium deposited on calcium carbonate and poisoned with lead acetate and quinoline.

Hydrogenolysis is a chemical reaction where a carbon-heteroatom bond, such as a carbon-oxygen or carbon-nitrogen bond, is cleaved by the addition of hydrogen. This process is commonly used in organic chemistry for the selective removal of protecting groups and the reduction of various functional groups.

Catalytic Hydrogenation: A chemical reaction where hydrogen gas (H2) is added to a substrate in the presence of a catalyst, typically a transition metal, to reduce unsaturated bonds such as alkenes and alkynes.

Reductive Cleavage: The process of breaking a chemical bond by the addition of hydrogen, often used to remove protecting groups or reduce functional groups in organic synthesis.

Heterolytic Bond Cleavage: A type of bond cleavage where the bonding electrons are unequally distributed between the two atoms, resulting in the formation of a cation and an anion.