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🥼Organic Chemistry
🥼organic chemistry review
17.4 Alcohols from Carbonyl Compounds: Reduction
2 min read•Last Updated on May 7, 2024
Carbonyl compounds can be transformed into alcohols through reduction reactions. This process involves adding hydrogen atoms to the carbonyl group, changing its oxidation state. The choice of reducing agent, like NaBH4 or LiAlH4, affects the reaction's strength and selectivity.
Different carbonyl compounds yield specific alcohol types when reduced. Aldehydes become primary alcohols, while ketones form secondary alcohols. Carboxylic acids and esters can also be reduced to primary alcohols, but require stronger reducing agents like LiAlH4.
Reduction of Carbonyl Compounds to Alcohols
Reduction of aldehydes and ketones
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- Aldehydes and ketones reduced to alcohols using hydride reducing agents ( or )
- Aldehydes reduced to primary alcohols (carbonyl carbon has one alkyl or aryl group attached)
- Ketones reduced to secondary alcohols (carbonyl carbon has two alkyl or aryl groups attached)
- Reduction process involves addition of hydride ion () to carbonyl carbon and proton () to carbonyl oxygen
- Forms new carbon-hydrogen bond and hydroxyl group () at former carbonyl carbon
- Example: Reduction of acetone (ketone) to 2-propanol (secondary alcohol) using
- Reduction involves nucleophilic addition of hydride to the carbonyl group
NaBH4 vs LiAlH4 as reducing agents
- and commonly used hydride reducing agents for reduction of carbonyl compounds to alcohols
- milder reducing agent compared to
- Selectively reduces aldehydes and ketones to alcohols
- Does not reduce carboxylic acids, esters, or amides
- Used in protic solvents (methanol or ethanol)
- stronger reducing agent compared to
- Reduces aldehydes, ketones, carboxylic acids, esters, and amides to alcohols
- Must be used in aprotic solvents (diethyl ether or THF) due to reactivity with protic solvents
- Example: Reduction of ethyl acetate (ester) to ethanol (primary alcohol) using
- Reduction potential affects the strength and selectivity of reducing agents
Reduction of carboxylic acids and esters
- Carboxylic acids and esters reduced to primary alcohols using
- preferred reducing agent due to higher reactivity compared to
- Reduction of carboxylic acids to primary alcohols:
- Addition of four hydrogen atoms (two molecules)
- Proceeds through aldehyde intermediate, further reduced to primary alcohol
- Overall reaction:
- Example: Reduction of acetic acid to ethanol using
- Reduction of esters to primary alcohols:
- Addition of four hydrogen atoms (two molecules)
- Proceeds through aldehyde intermediate, further reduced to primary alcohol
- Overall reaction:
- Also produces alcohol () derived from alkoxy group of ester
- Example: Reduction of methyl benzoate to benzyl alcohol and methanol using
Stereochemistry and Oxidation State in Carbonyl Reductions
- Reduction of carbonyl compounds decreases the oxidation state of the carbon atom
- Stereochemistry of the product depends on the structure of the starting material and the reducing agent
- The transition state during reduction influences the stereochemical outcome of the reaction
Key Terms to Review (40)
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.
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.
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.
Protic solvents: Protic solvents are substances that have a hydrogen atom attached to an oxygen (as in alcohol or water) or nitrogen atom, making them capable of forming hydrogen bonds. They play a crucial role in facilitating SN2 reactions by stabilizing the transition state and reactants through hydrogen bonding.
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.
Nucleophilic addition reaction: A nucleophilic addition reaction is a chemical process where a nucleophile forms a bond with an electrophilic carbon atom of a compound, typically found in aldehydes and ketones. This reaction results in the conversion of the carbonyl group into a more complex, often larger, molecule.
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.
Polar aprotic solvents: Polar aprotic solvents are solvents that have a net dipole moment but do not possess hydrogen atoms capable of forming hydrogen bonds. They are used in organic reactions to dissolve electrolytes and facilitate reactions without participating in them.
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.
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.
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.
Amide: An amide is a functional group consisting of a carbonyl group (C=O) linked to a nitrogen atom (N). Amides are important in organic chemistry and play a crucial role in various topics, including functional groups, elimination reactions, alcohol reduction, nitrile chemistry, amide chemistry, and the spectroscopy of carboxylic acid derivatives.
Nucleophilic Addition: Nucleophilic addition is a fundamental organic reaction in which a nucleophile, a species that donates electrons, adds to an electrophilic carbon center, typically a carbonyl carbon, to form a new product. This reaction is central to understanding many important topics in organic chemistry, including functional groups, polar reactions, carbocation stability, reaction stereochemistry, and the chemistry of aldehydes, ketones, alcohols, and other carbonyl-containing compounds.
Acetone: Acetone is a simple organic compound with the chemical formula CH3COCH3. It is a colorless, volatile, flammable liquid that is widely used as a solvent and in various chemical processes. Acetone is a key term that is relevant in the context of several important organic chemistry topics.
Ethyl Acetate: Ethyl acetate is a versatile organic compound that serves as a common solvent, a flavoring agent, and an important intermediate in various chemical reactions. It is the ester formed by the reaction between acetic acid and ethanol, and its diverse applications make it a crucial compound in both laboratory and industrial settings.
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.
Ester: An ester is a chemical compound formed by the reaction between an organic acid and an alcohol, resulting in the replacement of the hydrogen atom of the acid by an alkyl or aryl group. Esters are widely encountered in various topics in organic chemistry, including functional groups, oxidation-reduction reactions, alcohol formation, and spectroscopy.
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.
Acetic Acid: Acetic acid is a weak organic acid with the chemical formula CH3COOH. It is a colorless liquid with a distinctive sour odor and is the main component of vinegar. Acetic acid is a versatile compound that plays important roles in various organic chemistry topics, including functional groups, oxidation of alkenes, reduction of carbonyl compounds, naming of carboxylic acids, and the chemistry of esters.
Methyl Benzoate: Methyl benzoate is an organic compound that consists of a benzene ring with a carboxyl group (-COOH) attached, and a methyl group (-CH3) esterified to the carboxyl group. It is a colorless liquid with a sweet, fruity odor and is commonly used as a flavoring agent and in the production of various chemical compounds.
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.
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.
Hydroxyl Group: The hydroxyl group (OH-) is a functional group consisting of an oxygen atom covalently bonded to a hydrogen atom. It is a key structural feature in many organic compounds, particularly alcohols and phenols, and plays a crucial role in their chemical properties and reactivity.
Oxidation State: Oxidation state is a measure of the degree of oxidation of an atom in a chemical compound. It is the hypothetical charge that an atom would have if all bonds to atoms of different elements were completely ionic, with the more electronegative atom(s) assigned the full negative charge(s).
THF: THF, or tetrahydrofuran, is a cyclic ether compound that is commonly used as a solvent and in various organic chemistry reactions. It is a versatile and widely-used chemical that plays a crucial role in several important topics in organic chemistry.
Lithium Aluminum Hydride: Lithium aluminum hydride (LiAlH4) is a powerful reducing agent used in organic chemistry for the selective reduction of various functional groups. It is a white, crystalline solid that reacts violently with water and other protic solvents, making it an important reagent in many synthetic transformations.
Diethyl Ether: Diethyl ether is a colorless, highly volatile, and flammable liquid ether that has been widely used as an anesthetic, as a solvent, and in various organic chemistry reactions. It is an important compound that is closely tied to several key topics in organic chemistry.
Aprotic Solvent: An aprotic solvent is a type of organic solvent that does not contain an active hydrogen atom and does not participate in hydrogen bonding. These solvents are commonly used in various organic chemistry reactions, including the E1 and E1cB reactions, the reduction of carbonyl compounds, the Wittig reaction, and the Claisen condensation reaction.
Sodium Borohydride: Sodium borohydride is a powerful reducing agent commonly used in organic chemistry reactions to reduce carbonyl compounds to alcohols. It is a versatile reagent that finds applications in various topics, including the reduction of aromatic compounds, the preparation of alcohols, the synthesis of ethers, and the nucleophilic addition of hydride to carbonyl groups.
Primary Alcohol: A primary alcohol is an organic compound containing a hydroxyl (-OH) functional group attached to a saturated carbon atom that is bonded to only one other carbon atom. Primary alcohols are an important class of organic compounds with diverse applications and are a key focus in the study of organic chemistry.
Carbonyl Compound: A carbonyl compound is a class of organic compounds that contain a carbonyl group, which is a carbon atom double-bonded to an oxygen atom. These compounds are fundamental in organic chemistry and play a crucial role in various reactions and transformations, including the topics of alcohols from carbonyl compounds, the Wolff-Kishner reduction, nucleophilic acyl substitution, enolate ion formation, alkylation of enolate ions, and intramolecular aldol reactions.
Secondary Alcohol: A secondary alcohol is an organic compound in which a hydroxyl group (-OH) is attached to a carbon atom that is bonded to two other carbon atoms. This structural feature distinguishes secondary alcohols from primary alcohols, where the hydroxyl group is attached to a carbon atom bonded to only one other carbon, and tertiary alcohols, where the hydroxyl group is attached to a carbon atom bonded to three other carbons.
Reduction Potential: Reduction potential is a measure of the tendency of a chemical species to acquire electrons and be reduced. It is a fundamental concept in electrochemistry that describes the driving force for redox (reduction-oxidation) reactions, where one species is reduced by accepting electrons while another is oxidized by donating electrons.
Protic Solvent: A protic solvent is a type of solvent that contains hydrogen atoms bonded to highly electronegative atoms, such as oxygen or nitrogen, and can donate protons (H+) to solutes. This ability to donate protons makes protic solvents excellent for facilitating reactions involving the transfer of protons, such as acid-base reactions and some nucleophilic additions.
2-propanol: 2-propanol, also known as isopropyl alcohol or isopropanol, is a colorless, flammable liquid with a characteristic odor. It is an important organic compound that is widely used in various applications, including as a solvent, disinfectant, and in the synthesis of other chemicals.
Aldehyde Intermediate: An aldehyde intermediate is a transient chemical species that contains a carbonyl group (C=O) with a hydrogen atom attached to the carbon. These intermediates often arise in organic reactions and play a crucial role in the transformation of carbonyl compounds, such as the reduction of aldehydes to alcohols and the formation of amides from carboxylic acids.
Hydride Reducing Agent: A hydride reducing agent is a compound that can donate a hydride ion (H-) to reduce carbonyl compounds, such as aldehydes and ketones, to alcohols. These reducing agents are commonly used in the context of 17.4 Alcohols from Carbonyl Compounds: Reduction, where they facilitate the conversion of carbonyl groups to hydroxyl groups.
Hydride Ion: The hydride ion, denoted as H⁻, is a negatively charged hydrogen atom that has gained an extra electron, making it a powerful reducing agent. This term is particularly relevant in the context of the reduction of carbonyl compounds to alcohols, as described in the topic 17.4 Alcohols from Carbonyl Compounds: Reduction.
Benzyl Alcohol: Benzyl alcohol is an aromatic alcohol with the chemical formula C6H5CH2OH. It is a clear, colorless liquid with a mild, sweet odor. Benzyl alcohol is an important compound in organic chemistry, with applications in the synthesis of various organic compounds and as a preservative in pharmaceutical and personal care products.
Carbonyl Carbon: The carbonyl carbon is the central carbon atom in a carbonyl group, which is a functional group consisting of a carbon atom double-bonded to an oxygen atom. This carbonyl carbon is a key structural feature in various organic compounds, including aldehydes, ketones, carboxylic acids, and their derivatives, and plays a crucial role in the reactivity and properties of these compounds.