8.4 Hydration of Alkenes: Addition of H2O by Oxymercuration
2 min read•may 7, 2024
Alkenes can be transformed into alcohols through reactions. Two key methods are ###-Demercuration_0### and , both following ###'s_Rule_0### for .
Oxymercuration-demercuration offers milder conditions and avoids rearrangements, while acid-catalyzed hydration is simpler but can cause rearrangements. Understanding these processes is crucial for synthesizing alcohols from alkenes effectively.
Hydration of Alkenes
Oxymercuration-demercuration process
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Organic chemistry 20: Alkenes - oxymercuration, hydroboration View original
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Organic chemistry 20: Alkenes - oxymercuration, hydroboration View original
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Top images from around the web for Oxymercuration-demercuration process
Organic chemistry 20: Alkenes - oxymercuration, hydroboration View original
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Organic chemistry 20: Alkenes - oxymercuration, hydroboration View original
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Organic chemistry 20: Alkenes - oxymercuration, hydroboration View original
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Organic chemistry 20: Alkenes - oxymercuration, hydroboration View original
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- Two-step process converts alkenes to alcohols
- Oxymercuration step
- Alkene reacts with (Hg(OAc)2) in water
- of Hg-OH across the double bond forms a intermediate
- Demercuration step
- Sodium (NaBH4) reduces the mercurinium ion
- Breaks the mercury-carbon bond and replaces mercury with hydrogen
- Yields the final product (, )
- Oxymercuration step
- : Results in overall of H and OH groups
Markovnikov's rule in alkene hydration
- Predicts regioselectivity of alkene addition reactions based on stability
- More stable carbocation intermediate forms preferentially
- More highly substituted carbocations are more stable (tertiary > secondary > primary)
- In oxymercuration-demercuration, OH group attaches to the more substituted carbon of the alkene forming the Markovnikov product
- Example: undergoes oxymercuration-demercuration
- OH adds to the tertiary carbon yielding
Acid-catalyzed vs oxymercuration-demercuration hydration
- Acid-catalyzed hydration
- Alkene reacts with water and a strong acid catalyst (H2SO4)
- Proceeds through a carbocation intermediate yielding Markovnikov alcohol product
- Advantages
- Simple, one-step process
- Inexpensive reagents (water, sulfuric acid)
- Limitations
- Rearrangements can occur due to carbocation intermediate
- Not suitable for acid-sensitive substrates (alcohols, amines)
- Oxymercuration-demercuration
- Two-step process: oxymercuration followed by demercuration
- Proceeds through a mercurinium ion intermediate yielding Markovnikov alcohol product
- Advantages
- Milder conditions compared to acid-catalyzed hydration
- No rearrangements due to the more stable mercurinium ion intermediate
- Tolerates acid-sensitive substrates
- Limitations
- Two-step process is more time-consuming
- Uses toxic mercury compounds requiring proper disposal
Reaction Considerations
- : Water acts as both solvent and in the reaction
- Regioselectivity: Follows Markovnikov's rule due to the formation of the mercurinium ion intermediate
- : Rate-determining step is the initial formation of the mercurinium ion
Key Terms to Review (30)
2-methyl-2-butanol: 2-methyl-2-butanol is an organic compound with the chemical formula C5H12O. It is a secondary alcohol, meaning the hydroxyl group (-OH) is attached to a carbon atom that is bonded to two other carbon atoms. This term is particularly relevant in the context of the topics 8.4 Hydration of Alkenes: Addition of H2O by Oxymercuration and 19.7 Nucleophilic Addition of Hydride and Grignard Reagents: Alcohol Formation, as it represents a key product that can be formed through these reactions.
2-methylbut-2-ene: 2-methylbut-2-ene is an organic compound with the molecular formula C₅H₁₀. It is an alkene with a methyl group (CH₃) attached to the second carbon of the four-carbon chain. This term is particularly relevant in the context of understanding Markovnikov's rule for the orientation of electrophilic additions and the hydration of alkenes through the process of oxymercuration.
Acid-Catalyzed Hydration: Acid-catalyzed hydration is a chemical reaction where an alkene (a molecule containing a carbon-carbon double bond) reacts with water in the presence of an acid catalyst to form an alcohol. This process is an important reaction in the context of the addition of H2O by oxymercuration, a method for the hydration of alkenes.
Addition Reaction: An addition reaction is a type of chemical reaction where two or more reactants combine to form a single product. In the context of organic chemistry, addition reactions typically involve the addition of atoms or molecules to an alkene or alkyne, resulting in the formation of a new compound with a different structure and properties.
Alcohol: In the context of organic chemistry, an alcohol is an organic compound in which a hydroxyl group (-OH) is bonded to a saturated carbon atom. The general formula for a simple alcohol can be represented as CnH2n+1OH, where n is the number of carbon atoms.
Alcohol: Alcohols are a class of organic compounds characterized by the presence of a hydroxyl (-OH) functional group attached to a saturated carbon atom. They are widely used in various chemical reactions and have diverse applications in organic synthesis, pharmaceutical industry, and everyday life.
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.
Anti-Addition: Anti-addition is a type of organic reaction mechanism in which the incoming electrophile or nucleophile adds to the opposite side of the double bond, resulting in the formation of the opposite regioisomer compared to the typical addition reaction. This term is particularly relevant in the context of electrophilic addition reactions of alkenes, the hydration of alkenes via oxymercuration, and the reduction of alkynes.
Anti-Addition Mechanism: The anti-addition mechanism is a type of addition reaction that occurs when a nucleophile and an electrophile approach a carbon-carbon double bond from opposite sides, resulting in the formation of the anti-addition product. This mechanism is particularly relevant in the context of the hydration of alkenes through the process of oxymercuration.
Borohydride: Borohydride, also known as sodium borohydride, is a reducing agent commonly used in organic chemistry reactions, particularly in the context of the hydration of alkenes through the addition of water by oxymercuration.
Carbocation: A carbocation is a positively charged carbon atom that is part of an organic molecule. These reactive intermediates play a crucial role in various organic reactions, including electrophilic additions, nucleophilic substitutions, and elimination reactions.
Electrophilic Addition: Electrophilic addition is a type of organic reaction where an electrophile, a species that is attracted to electrons, adds to the carbon-carbon double bond of an alkene. This results in the formation of a new carbon-carbon single bond and the incorporation of the electrophile into the molecule.
Electrophilic addition reaction: An electrophilic addition reaction is a chemical process in which an electrophile reacts with a nucleophile, typically an alkene or alkyne, forming a new sigma bond by adding across the double or triple bond. This reaction is key in organic synthesis, resulting in the addition of atoms or groups to the carbon atoms involved in the multiple bond.
Ethanol: Ethanol, also known as ethyl alcohol, is a colorless, volatile, and flammable liquid that is the principal type of alcohol found in alcoholic beverages. It is an important organic compound with diverse applications in various fields, including as a fuel, solvent, and chemical feedstock.
Hydration: Hydration is the process of adding water to a chemical compound, typically involving the addition of water across a double bond or the incorporation of water into the structure of a molecule. This term is particularly relevant in the context of organic chemistry, where it plays a crucial role in various reactions and transformations.
Isopropanol: Isopropanol, also known as isopropyl alcohol or 2-propanol, is a secondary alcohol with the chemical formula C$_3$H$_8$O. It is an important organic compound with various applications, particularly in the context of the topics 'Hydration of Alkenes: Addition of H$_2$O by Oxymercuration' and 'Spectroscopy of Alcohols and Phenols'.
Markovnikov: Markovnikov is a principle that describes the preferred regiochemistry of electrophilic addition reactions to unsymmetrical alkenes. It states that in the addition of an unsymmetrical reagent, such as a hydrogen halide, to an alkene, the electrophilic portion of the reagent will add to the carbon of the alkene that can best stabilize the resulting carbocation intermediate.
Markovnikov’s rule: Markovnikov's rule predicts the outcome of the electrophilic addition of hydrogen halides to alkenes, stating that the hydrogen atom will attach to the carbon with more hydrogen atoms, and the halide will attach to the more substituted carbon. This rule helps in determining the major product of addition reactions in organic chemistry.
Markovnikov's Rule: Markovnikov's rule is a principle in organic chemistry that describes the orientation of addition reactions involving unsaturated compounds, such as alkenes. It states that in the addition of a hydrogen halide (HX) to an alkene, the hydrogen atom of the HX bond attaches to the carbon atom of the alkene that can best stabilize the resulting carbocation intermediate.
Mercuric Ion: The mercuric ion, denoted as Hg2+, is a positively charged ion of the element mercury. It is a key component in the chemical process known as oxymercuration, which is a method for the hydration of alkenes, adding water across the carbon-carbon double bond.
Mercurinium Ion: The mercurinium ion is a reactive intermediate formed during the oxymercuration-demercuration reaction, a common method for the hydration of alkenes to form alcohols. It is a key species involved in the preparation of alcohols and ethers.
Mercury(II) Acetate: Mercury(II) acetate, also known as basic mercuric acetate, is a chemical compound with the formula Hg(CH3COO)2. It is a white crystalline solid that is commonly used as a reagent in organic chemistry reactions, particularly in the hydration of alkenes and the preparation of alcohols.
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.
Oxymercuration: Oxymercuration is a chemical reaction that involves the addition of water to an alkene or alkyne in the presence of a mercury(II) salt, typically mercury(II) acetate. This process is used to introduce a hydroxyl group (-OH) to the molecule, effectively hydrating the carbon-carbon double or triple bond.
Oxymercuration-Demercuration: Oxymercuration-demercuration is a two-step organic reaction that is used to add water to alkenes, resulting in the formation of alcohols. It involves the initial addition of a mercury-containing compound, followed by the removal of the mercury to yield the final alcohol product.
Oxymercuration–demercuration: Oxymercuration–demercuration is a two-step organic chemical reaction process that adds water (H2O) across the double bond of alkenes, in a regioselective manner, to form alcohols without the rearrangement typically seen in acid-catalyzed hydration. First, oxymercuration involves the addition of mercury acetate and water across the alkene's double bond, followed by demercuration, where sodium borohydride reduces the intermediate to produce an alcohol.
Reaction Kinetics: 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.
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.
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.