18.4 Cyclic Ethers: Epoxides
2 min read•may 7, 2024
Epoxides are versatile compounds with a strained containing oxygen. They're synthesized through or routes, each with distinct stereochemical outcomes. Industrially, is a key used in antifreeze and detergent production.
Epoxides are more reactive than other ethers due to , readily undergoing reactions. This reactivity makes them valuable in organic synthesis. Factors like substitution patterns and solvents influence the and rate of these reactions.
Synthesis and Reactivity of Epoxides
Synthesis of epoxides
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- Peroxyacid synthesis involves electrophilic addition of peroxyacid (mCPBA) to alkene followed by intramolecular nucleophilic substitution retaining with oxygen adding to same face of alkene
- Halohydrin synthesis forms halohydrins by addition of halogen (X) and hydroxyl group (OH) to alkene then intramolecular reaction with strong base (NaOH) forms epoxide inverting stereochemistry due to backside attack
- The stereochemistry of the product is determined by the of this reaction
Industrial production of ethylene oxide
- Produced by direct oxidation of ethylene with oxygen over at 200-300°C and 10-30 atm pressure purified through distillation
- Used for production by hydrolysis as antifreeze and polyester fiber precursor
- of fatty alcohols produces and detergents
- for heat-sensitive medical equipment and supplies
Reactivity of epoxides vs ethers
- Epoxides have significant ring strain due to 60° bond angles deviating from ideal 109.5° for hybridized carbons making them more reactive than cyclic and acyclic ethers
- Readily undergo reactions with water, alcohols, amines, and halides attacking either carbon leading to various products with regioselectivity depending on and epoxide substitution
- The regioselectivity can be influenced by of the epoxide carbons
- Acyclic ethers (diethyl ether) are relatively unreactive due to absence of ring strain and low polarity of C-O bond
- Cyclic ethers (THF) are more reactive than acyclic but less than epoxides due to reduced ring strain
Reaction Mechanisms and Solvent Effects
- The for epoxide ring-opening typically involves nucleophilic attack at the less substituted carbon
- can significantly influence the rate and outcome of epoxide reactions, with polar protic solvents often accelerating nucleophilic ring-opening
Key Terms to Review (36)
Acidic Conditions: Acidic conditions refer to an environment with a high concentration of hydrogen ions (H+), resulting in a low pH value typically below 7. This type of environment is commonly encountered in various chemical reactions and processes, including those involving cyclic ethers like epoxides.
Anti Addition: Anti addition refers to the stereochemical outcome of an electrophilic addition reaction, where the incoming electrophilic species adds to the opposite face of the alkene or alkyne relative to the existing substituents. This results in the formation of the anti-addition product, where the new substituents are arranged in an anti-configuration.
Anti stereochemistry: Anti stereochemistry describes the spatial arrangement in a chemical reaction where two substituents are positioned on opposite sides of a double bond or ring structure after the reaction. It is particularly relevant in the halogenation of alkenes, resulting in products where the added atoms are located across from each other.
Basic Conditions: Basic conditions refer to a chemical environment with a high concentration of hydroxide ions (OH-), resulting in a pH greater than 7. This environment is often used in organic chemistry reactions to facilitate specific transformations, particularly in the context of cyclic ethers and epoxides.
Cyclic Ether: A cyclic ether is a type of organic compound that contains an oxygen atom incorporated into a ring structure. These compounds are characterized by the presence of an ether functional group within a closed-loop arrangement of atoms.
Electrophile: An electrophile is a species that is attracted to electron-rich regions and seeks to form new bonds by accepting electron density. Electrophiles play a crucial role in many organic reactions, including polar reactions, electrophilic aromatic substitution, and nucleophilic acyl substitution, among others.
Epoxidation: Epoxidation is a chemical reaction that converts alkenes (carbon-carbon double bonds) into cyclic ethers called epoxides. This process involves the addition of an oxygen atom across the double bond, creating a three-membered ring structure. Epoxidation is an important transformation in organic chemistry, with applications in the synthesis of various compounds and the production of polymers.
Epoxide: An epoxide is a cyclic ether compound containing a three-membered ring consisting of one oxygen atom and two carbon atoms. Epoxides are important intermediates in organic chemistry, particularly in the context of alkene oxidation, cyclic ether formation, and various ring-opening reactions.
Ethoxylation: Ethoxylation is a chemical reaction in which ethylene oxide is added to a compound, typically an alcohol or a fatty acid, to produce an ethoxylated derivative. This process is widely used in the production of surfactants, detergents, and other industrial and consumer products.
Ethylene Glycol: Ethylene glycol is a colorless, odorless, and sweet-tasting liquid that is widely used as an antifreeze, coolant, and solvent. It is a dihydric alcohol, meaning it contains two hydroxyl groups, and its chemical formula is C₂H₆O₂. Ethylene glycol is a versatile compound that is relevant in the context of various topics in organic chemistry, including spectroscopy of alcohols and phenols, cyclic ethers, reactions of epoxides, and the synthesis of step-growth polymers.
Ethylene Oxide: Ethylene oxide is a colorless, flammable gas that is widely used in industrial and medical applications. It is a cyclic ether with the chemical formula C₂H₄O, and it serves as a key intermediate in the production of various chemicals and materials.
Gaseous Sterilant: A gaseous sterilant is a chemical agent in the form of a gas that is used to kill or inactivate microorganisms, including bacteria, viruses, fungi, and spores, on surfaces and in enclosed environments. These sterilants are commonly employed in medical and pharmaceutical settings to ensure the sterility of equipment, instruments, and facilities.
Halohydrin: A halohydrin is a compound containing both a halogen atom (such as chlorine, bromine, or iodine) and a hydroxyl group (-OH) on adjacent carbon atoms. These compounds are formed through the addition of a hydrogen halide (HX, where X is a halogen) to an alkene, resulting in the incorporation of both the halogen and the hydroxyl group.
M-CPBA: m-CPBA, or meta-Chloroperoxybenzoic acid, is an important organic oxidizing agent commonly used in the synthesis of epoxides, a class of cyclic ethers, through a process known as epoxidation.
Non-Ionic Surfactants: Non-ionic surfactants are a class of surfactants that do not carry an electric charge, unlike ionic surfactants. They are widely used in various applications, including the context of cyclic ethers and epoxides, due to their unique properties and versatility.
Nucleophile: A nucleophile is a species that donates a pair of electrons to form a covalent bond with another atom or molecule. Nucleophiles are central to understanding many organic reactions, including polar reactions, electrophilic addition reactions, and nucleophilic substitution reactions.
Nucleophilic Ring-Opening: Nucleophilic ring-opening is a reaction in which a nucleophile attacks and breaks open a cyclic ether, such as an epoxide, to form a new linear ether or alcohol product. This process is an important transformation in organic chemistry, particularly in the context of cyclic ethers like epoxides.
Oxirane: Oxirane, also known as ethylene oxide, is a cyclic ether with the chemical formula C2H4O. It is the simplest epoxide, a class of cyclic ethers characterized by a three-membered ring containing one oxygen atom and two carbon atoms.
Peroxyacid: A peroxyacid is an organic compound that contains a peroxide functional group (-O-O-) attached to a carboxylic acid group (-COOH). These compounds are important intermediates in various organic reactions, particularly in the synthesis of epoxides, a class of cyclic ethers.
Prilezhaev Reaction: The Prilezhaev reaction is a chemical reaction used to synthesize epoxides, which are cyclic ethers containing an oxygen atom and two carbon atoms in a three-membered ring. This reaction is particularly relevant in the context of the topics covered in Section 18.4 Cyclic Ethers: Epoxides.
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.
Regioselectivity: Regioselectivity refers to the preference of a chemical reaction to occur at a specific site or region of a molecule, leading to the formation of one regioisomeric product over another. This concept is particularly important in the context of electrophilic addition reactions of alkenes, electrophilic aromatic substitution, and other organic transformations.
Ring Strain: Ring strain refers to the inherent instability and high-energy state of cyclic organic compounds, particularly those with small ring sizes, due to the distortion of bond angles and bond lengths from their ideal values. This concept is central to understanding the properties and reactivity of cycloalkanes and other cyclic structures.
Ring-Opening: Ring-opening is a chemical process in which a cyclic compound, such as an epoxide, undergoes a reaction that breaks the ring structure, forming a linear or acyclic product. This term is particularly relevant in the context of cyclic ethers, specifically epoxides, and their subsequent reactions.
Sharpless epoxidation: Sharpless epoxidation is a chemical reaction that selectively transforms primary and secondary allylic alcohols into their corresponding epoxy alcohols using titanium tetraisopropoxide, tert-butyl hydroperoxide, and diethyl tartrate. It is noteworthy for its stereospecificity, predominantly producing molecules with a specific three-dimensional arrangement.
Sharpless Epoxidation: The Sharpless epoxidation is a chemical reaction used to synthesize epoxides, which are cyclic ethers containing three-membered rings. It is a highly selective and efficient method for the stereoselective formation of epoxides from allylic alcohols.
Silver Catalyst: A silver catalyst is a type of heterogeneous catalyst that is commonly used in various organic reactions, particularly in the context of cyclic ether formation, such as epoxides. These catalysts facilitate the reaction by providing a surface for the reactants to adsorb and interact, thereby lowering the activation energy required for the transformation to occur.
Solvent Effects: Solvent effects refer to the influence that the surrounding solvent environment can have on the behavior and properties of chemical reactions, molecules, and spectroscopic measurements. The nature and polarity of the solvent can significantly impact the energetics, kinetics, and outcomes of various organic chemistry processes.
Stereochemistry: 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.
Stereoisomer: Stereoisomers are molecules that have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space. This variation can significantly affect the physical and chemical properties of the compounds.
Stereoisomer: Stereoisomers are molecules that have the same molecular formula and connectivity, but differ in the spatial arrangement of their atoms. This term is particularly relevant in the context of organic chemistry, as it helps explain the diverse structures and properties of various compounds.
Steric Hindrance: Steric hindrance, also known as steric strain or steric effect, refers to the repulsive forces that arise between atoms or groups of atoms in a molecule due to their physical size and spatial arrangement. This phenomenon can significantly impact the stability, reactivity, and conformations of organic compounds.
Three-Membered Ring: A three-membered ring is a cyclic organic compound containing three atoms in its ring structure. These small, strained rings are commonly found in the context of cyclic ethers, such as epoxides, and have unique chemical properties and reactivity.
Transition state: In organic chemistry, the transition state is a high-energy, temporary condition where reactants are transformed into products during a chemical reaction. It represents the point of maximum energy on the energy diagram before the formation of products.
Transition State: The transition state is a key concept in organic chemistry that describes the highest-energy intermediate along the reaction pathway. It represents the point where the reactants are being converted into products, with the system at its most unstable and energetically unfavorable configuration.