Aldehydes and Ketones

The Organic Chemistry Tutor

4 May 201873:40

EducationalLearning

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TLDRThis chemistry video delves into the reactions of ketones and aldehydes, focusing on reduction reactions using sodium borohydride and lithium aluminum hydride, which convert these compounds into various types of alcohols. It explores mechanisms, reactivity differences, and the impact of structure on reaction pathways. The script also covers reactions with Grignard reagents, the formation of imines and enamines, reductive amination, and the use of protecting groups. Additionally, it discusses the Bayer-Villiger oxidation, the Wittig reaction for converting ketones into alkenes, and the distinction between direct and conjugate addition reactions in alpha-beta unsaturated carbonyl compounds.

Takeaways

🧪 Sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4) are reducing agents that can convert ketones and aldehydes into alcohols through the addition of hydride ions.
🔍 The reduction mechanism involves the hydride ion attacking the carbonyl carbon, forming an alkoxide ion, which then reacts with H3O+ to form an alcohol.
📚 Sodium borohydride is not strong enough to reduce esters and carboxylic acids, while lithium aluminum hydride can reduce a wider range of functional groups, including esters and acid chlorides.
⚠️ Acid chlorides are highly reactive and can be reduced with mild reducing agents like sodium borohydride to form alcohols, with the chloride ion leaving as a side product.
🔄 The reduction of acid chlorides to alcohols involves an initial attack by the hydride ion, formation of a tetrahedral intermediate, and subsequent expulsion of the chloride ion.
🛠️ Reagents like lithium aluminum hydride with three OR groups (e.g., LiAlH(OR)3) can reduce acid chlorides to aldehydes by stopping the reduction process at the aldehyde level due to limited hydrogen atoms.
🔬 The mechanism of ester reduction by lithium aluminum hydride involves the breaking of the carbonyl group and the formation of an alcohol, with the leaving group picking up a hydrogen to form a separate molecule like methanol.
🧪 Amides, when reduced with lithium aluminum hydride, are converted to amines rather than alcohols, with the carbonyl group being reduced to a CH2 group.
🔬 The reduction of nitriles to primary amines involves the addition of hydrogen across the triple bond, facilitated by a catalyst like Raney nickel.
🌐 The reaction of aldehydes with Grignard reagents leads to the formation of alcohols through nucleophilic attack on the carbonyl carbon, followed by protonation to form the final alcohol product.
📐 The formation of imines from ketones and primary amines involves the removal of water and the formation of a carbon-nitrogen double bond, with the reaction being reversible.

Q & A

What happens when a ketone or an aldehyde reacts with sodium borohydride followed by H3O+?
-Sodium borohydride (NaBH4) reduces a ketone or an aldehyde to an alcohol. The reaction involves the hydride ion from NaBH4 attacking the carbonyl carbon, forming an alkoxide ion, which then reacts with H3O+ to yield a secondary alcohol.
How does lithium aluminum hydride (LiAlH4) affect the carbonyl group of an aldehyde?
-Lithium aluminum hydride reduces the carbonyl group of an aldehyde to an alcohol, resulting in a primary alcohol. The mechanism involves the reduction of the carbonyl group by the hydride ion from LiAlH4, followed by protonation to form the alcohol.
Why is sodium borohydride not strong enough to reduce esters and carboxylic acids?
-Sodium borohydride is a mild reducing agent and is not strong enough to reduce the carbonyl groups in esters and carboxylic acids due to their higher resistance to nucleophilic attack compared to ketones and aldehydes.
What is the major product when an acid chloride reacts with sodium borohydride followed by H3O+?
-The reaction of an acid chloride with sodium borohydride followed by H3O+ results in the reduction of the carbonyl group to an alcohol, with the chloride ion leaving as a side product.
How does the reduction of an acid chloride to an aldehyde occur with lithium aluminum hydride?
-Lithium aluminum hydride with three OR groups and one hydrogen (LiAlH(OR)3) can reduce an acid chloride to an aldehyde level. The reaction involves the hydride ion attacking the carbonyl carbon, forming a tetrahedral intermediate, which then expels the chloride ion to form the aldehyde.
What is the difference between the reduction of ketones to alcohols by Grignard reagents and by hydride ions?
-Grignard reagents add an R group to the carbonyl carbon, converting ketones into alcohols through the formation of an alkoxide ion and subsequent protonation. In contrast, hydride ions from reagents like NaBH4 or LiAlH4 directly reduce the carbonyl group to an alcohol without adding an R group.
What is the major product when an amide functional group is reduced with lithium aluminum hydride?
-The reduction of an amide with lithium aluminum hydride results in the formation of a primary amine, as the carbonyl group is reduced to a CH2 group.
How does the reductive amination of a ketone work, and what are the products?
-Reductive amination involves the reaction of a ketone with ammonia, followed by the removal of a water molecule, yielding an amine. The amine can then be reduced to an amide using hydrogen and a catalyst like palladium on carbon.
What is the significance of the migratory aptitude in the Bayer-Villiger oxidation reaction?
-In the Bayer-Villiger oxidation reaction, the migratory aptitude determines which group (R1 or R2) will migrate to the carbonyl carbon with the oxygen from the peroxy acid, forming an ester. Groups with higher migratory aptitude, such as hydrogen, are more likely to migrate.
How does the choice of reagent affect the type of addition reaction (direct or conjugate) with alpha-beta unsaturated ketones?
-The choice of reagent determines whether direct or conjugate addition occurs. Strong bases, like Grignard reagents, favor direct addition to the carbonyl carbon, while weak bases, like cyanide ions, favor conjugate addition to the beta carbon.

Outlines

00:00

🔬 Reduction Reactions of Ketones and Aldehydes

This paragraph discusses the reduction reactions of ketones and aldehydes using reagents like sodium borohydride and lithium aluminum hydride. It explains how these reagents reduce ketones and aldehydes into secondary and primary alcohols, respectively. The mechanism of the reduction reaction with sodium borohydride is detailed, highlighting the role of hydride ions and the formation of alkoxide ions.

05:08

🔬 Reduction of Esters and Acid Chlorides

This section covers the reduction of esters and acid chlorides using lithium aluminum hydride and sodium borohydride. It explains the different reactivities of esters and acid chlorides, detailing how sodium borohydride can reduce acid chlorides to alcohols, but not esters. The mechanism for reducing acid chlorides to aldehydes and further to alcohols is also discussed.

10:08

🔬 Reduction of Amides and Other Functional Groups

This part describes the reduction of amides to amines using lithium aluminum hydride. It also mentions additional educational resources available on Patreon, including detailed videos on organic chemistry reactions. Further reduction reactions involving hydrogen gas and palladium over carbon are explained, highlighting the conversion of alkenes, ketones, and aldehydes to alcohols.

15:13

🔬 Reactivity of Ketones with Grignard Reagents

This paragraph discusses the reaction of ketones and aldehydes with Grignard reagents to form alcohols. The mechanism involves the nucleophilic attack of the Grignard reagent on the carbonyl carbon, resulting in the formation of an alkoxide ion and subsequent protonation to yield alcohols. It also explains the formation of amines from ketones using primary and secondary amines under mild acidic conditions.

20:15

🔬 Formation of Imines and Enamines

This section covers the formation of imines and enamines from ketones using primary and secondary amines, respectively. The mechanism involves nucleophilic attack, proton transfers, and the expulsion of water. It highlights the differences in product formation when using primary versus secondary amines and provides step-by-step details of the reaction mechanism.

25:15

🔬 Reductive Amination and Protecting Groups

This part discusses reductive amination, converting ketones to amines using ammonia and hydrogenation. It also covers the use of protecting groups like ethylene glycol for selective reduction of esters without affecting ketones. Detailed mechanisms and examples of these reactions are provided, along with explanations of how different reagents affect the outcomes.

30:19

🔬 Reactivity of Aldehydes and Ketones

This paragraph explains the relative reactivity of aldehydes and ketones, noting that aldehydes are more reactive due to less steric hindrance and electron-donating effects of alkyl groups in ketones. It covers the formation of hydrates from aldehydes and ketones with water and the differences in their reactivities. The reactions of aldehydes and ketones with alcohols to form hemiacetals and acetals are also discussed.

35:21

🔬 Selective Reduction Strategies

This section describes strategies for selectively reducing ketones and esters using different reagents. It explains how sodium borohydride can reduce ketones but not esters, while lithium aluminum hydride can reduce both. The use of protecting groups to achieve selective reduction is detailed, along with the mechanism of thiol reactions under acidic conditions to form different types of protecting groups.

40:22

🔬 Converting Ketones to Alkanes

This part covers the conversion of ketones to alkanes using various reduction methods, including the Clemmensen reduction (zinc with mercury under acidic conditions) and the Wolff-Kishner reduction (hydrazine with a strong base and heat). It also discusses the oxidation of aldehydes with silver cations and the formation of carboxylate ions or carboxylic acids.

45:24

🔬 Wittig Reaction Mechanism

This paragraph explains the Wittig reaction, which converts ketones to alkenes using phosphonium ylides. The mechanism involves the formation of a four-membered ring intermediate and subsequent bond breaking to yield alkenes and triphenylphosphine oxide. Examples and step-by-step details of the Wittig reaction mechanism are provided.

50:28

🔬 Bayer-Villiger Oxidation Reaction

This section discusses the Bayer-Villiger oxidation reaction, where ketones are converted to esters using peroxy acids. It explains how to determine which alkyl group will migrate to form the ester and the relative migratory aptitudes of different groups. Several examples are provided to illustrate the application of this reaction.

55:28

🔬 Direct vs. Conjugate Addition Reactions

This part covers the direct and conjugate addition reactions to α,β-unsaturated carbonyl compounds. It explains how the nature of the nucleophile (strong vs. weak bases) and the steric hindrance around the carbonyl group influence the addition pathway. Examples of different nucleophiles and their preferred addition reactions are discussed.

00:29

🔬 Steric Effects on Addition Reactions

This paragraph explains how steric hindrance affects the direct and conjugate addition to α,β-unsaturated carbonyl compounds. It provides examples of ketones with varying degrees of steric hindrance and discusses how these factors influence the nucleophilic attack. The importance of both the strength of the base and steric factors in determining the major product is emphasized.

05:29

🔬 Mechanisms of Direct and Conjugate Addition

This section details the mechanisms of direct and conjugate addition reactions. It explains how strong bases like Grignard reagents prefer direct addition, while weak bases like cyanide ions favor conjugate addition. The mechanisms for both types of addition are illustrated with step-by-step descriptions and examples.

Mindmap

Keywords

💡Ketones

Ketones are organic compounds containing a carbonyl group (C=O) bonded to two carbon atoms. In the script, ketones are discussed in the context of reduction reactions, where they can be converted into alcohols using reagents like sodium borohydride or lithium aluminum hydride. The video explains that ketones can be reduced to secondary or primary alcohols depending on the reagent used, highlighting their importance in organic chemistry.

💡Aldehydes

Aldehydes are a class of organic compounds containing a carbonyl group with one carbon atom double-bonded to oxygen and single-bonded to hydrogen or an alkyl group. The script describes the reduction of aldehydes to primary alcohols using strong reducing agents like lithium aluminum hydride. Aldehydes are noted to be more reactive than ketones due to the absence of electron-donating alkyl groups.

💡Reduction Reaction

A reduction reaction in organic chemistry involves the gain of electrons or hydrogen atoms by a molecule. The video script discusses various reduction reactions, such as the conversion of ketones and aldehydes into alcohols using sodium borohydride or lithium aluminum hydride. These reactions are central to the theme of the video, illustrating the transformation of carbonyl compounds into other functional groups.

💡Sodium Borohydride (NaBH4)

Sodium borohydride is a reducing agent commonly used in organic chemistry for the reduction of ketones and aldehydes to alcohols. The script mentions its use in the reduction of ketones to secondary alcohols and its inability to reduce esters and carboxylic acids, which are less reactive due to the presence of electron-donating groups.

💡Lithium Aluminum Hydride (LiAlH4)

Lithium aluminum hydride is a strong reducing agent that can reduce a wide range of functional groups, including ketones, aldehydes, esters, and carboxylic acids to their corresponding alcohols. The script explains its use in reducing aldehydes to primary alcohols and its ability to reduce other functional groups, unlike sodium borohydride.

💡Ester

Esters are organic compounds formed by the reaction of an acid and an alcohol. The script discusses the reduction of esters to alcohols using lithium aluminum hydride, as sodium borohydride is not strong enough for this transformation. This highlights the difference in reactivity and the choice of reagent based on the functional group present.

💡Acid Chloride

An acid chloride is a compound containing a chlorinated carbonyl group. The script explains that acid chlorides are very reactive and can be reduced to alcohols using sodium borohydride or to aldehydes using a deactivator form of lithium aluminum hydride. The reduction mechanism involves nucleophilic attack and the formation of tetrahedral intermediates.

💡Amide

An amide is a functional group featuring a carbonyl group bonded to a nitrogen atom. The script describes the reduction of amides to primary amines using lithium aluminum hydride, illustrating a different reduction pathway compared to ketones and aldehydes, where the carbonyl group is reduced to a CH2 group instead of an OH group.

💡Enamine

An enamine is a compound formed by the addition of an amine to a ketone, resulting in a carbon-carbon double bond. The script explains the formation of enamines when secondary amines react with ketones under mild acidic conditions, leading to a nucleophilic attack by the nitrogen on the ketone's carbonyl carbon, and subsequent formation of a double bond between the carbon and nitrogen.

💡Reductive Amination

Reductive amination is a chemical reaction that converts ketones into amines through the initial formation of an imine, followed by a reduction step. The script describes this process using ketones and primary amines under mild acidic conditions, and the subsequent reduction using hydrogen and palladium over carbon to yield secondary amines.

💡Directed Addition

Directed addition refers to the specific pathway taken by a nucleophile in a chemical reaction, particularly in the context of alpha-beta unsaturated ketones. The script explains that strong bases preferentially attack the carbonyl carbon (direct addition), while weak bases tend to attack the beta carbon (conjugate addition). This concept is crucial for understanding the selectivity in nucleophilic addition reactions.

💡Conjugate Addition

Conjugate addition is a type of nucleophilic addition reaction that occurs at the beta carbon of an alpha-beta unsaturated carbonyl compound. The script discusses this reaction in the context of weak bases like the cyanide ion, which preferentially attack the beta carbon, leading to the formation of a new double bond and a nucleophilic group at the alpha carbon.

💡Bayer-Villiger Oxidation

Bayer-Villiger oxidation is a reaction where a ketone is oxidized to an ester by a peroxyacid. The script explains the process, emphasizing the migration of an R group to the carbonyl oxygen, which is determined by its migratory aptitude. This reaction is a key method for converting ketones into esters, with cyclic ketones forming lactones.

Highlights

Reduction reactions of ketones and aldehydes with sodium borohydride and lithium aluminum hydride can produce alcohols.

Sodium borohydride selectively reduces ketones and aldehydes to secondary and primary alcohols, respectively.

Lithium aluminum hydride reduces carbonyl groups to alcohols, applicable to aldehydes and ketones.

The mechanism of reduction involves hydride ion attack on the carbonyl carbon, forming an alkoxide ion intermediate.

Ester reduction with lithium aluminum hydride, unlike sodium borohydride, can yield alcohols.

Acid chlorides react with sodium borohydride to form alcohols, with chloride ions as side products.

Lithium aluminum hydride with three OR groups reduces acid chlorides to aldehydes, not alcohols.

Reduction of acid chlorides to alcohols involves a two-step process with sodium borohydride.

Carboxylic acids can be reduced to primary alcohols using lithium aluminum hydride.

Amides are reduced by lithium aluminum hydride to primary amines, not alcohols.

Cyclohexene reacts with hydrogen gas and palladium catalyst to form cyclohexane.

Ketones react with hydrogen gas and Raney nickel catalyst to form alcohols.

Aldehydes also react with hydrogen gas and Raney nickel to yield primary alcohols.

Reduction of nitriles to primary amines is achieved using hydrogen gas and Raney nickel catalyst.

Grignard reagents react with aldehydes to form secondary alcohols through nucleophilic attack.

Ketones react with Grignard reagents to form tertiary alcohols via nucleophilic addition.

Reductive amination converts ketones into amines by first forming an amine and then reducing it.

Enamines are formed by the reaction of ketones with secondary amines in mild acidic conditions.

The mechanism of amine formation from ketones involves reversible steps and proton transfers.

Enamine formation mechanism involves nucleophilic attack, proton transfers, and double bond formation.

Formaldehyde is more reactive than acetaldehyde and ketones due to less steric hindrance and more electrophilicity.

Aldehydes form hydrates readily with water, while ketones are less reactive and form hydrates minimally.

Hemiacetal and acetal formation reactions protect ketones from further nucleophilic attack.

Ketones can be selectively reduced without affecting esters by using sodium borohydride.

Lithium aluminum hydride reduces both ketones and esters to alcohols.

Protecting groups like acetals can be used to reduce esters without affecting ketones.

Ketones can be converted to alkanes through various reduction reactions like Clemmensen and Wolff-Kishner.

Aldehydes react with silver cation to form carboxylate ions under basic conditions, which can be acidified to carboxylic acids.

Cyanohydrins are formed by the reaction of ketones with hydrocyanic acid, leading to alpha-hydroxynitriles.

The Wittig reaction is a method for converting ketones into alkenes using phosphorane reagents.

The mechanism of the Wittig reaction involves the formation of a four-membered ring and subsequent bond rearrangement to form an alkene.

Baeyer-Villiger oxidation converts ketones into esters or lactones by oxygen insertion with peroxy acids.

The migration aptitude of substituents in Baeyer-Villiger oxidation determines the major product.

Directed addition versus conjugate addition in alpha-beta unsaturated ketones depends on the strength of the nucleophile and steric factors.

Strong bases like Grignard reagent favor direct addition to the carbonyl carbon, while weak bases favor conjugate addition to the beta carbon.

The mechanism of direct addition involves nucleophilic attack on the carbonyl carbon and protonation.

Conjugate addition mechanism involves attack on the beta carbon, followed by protonation of the alpha carbon.

Transcripts

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