20.6 Reactions of Carboxylic Acids: An Overview
2 min read•may 7, 2024
are versatile organic compounds with a range of important reactions. From nucleophilic acyl substitutions to reductions and decarboxylations, these reactions showcase the diverse chemistry of the carboxyl group.
Understanding carboxylic acid reactions is crucial for grasping organic synthesis. These reactions highlight the reactivity of the and provide key tools for transforming carboxylic acids into other functional groups like alcohols and esters.
Reactions of Carboxylic Acids
Categories of carboxylic acid reactions
Top images from around the web for Categories of carboxylic acid reactions
Nucleophilic acyl substitution - Wikipedia View original
Is this image relevant?
22.1: Introduction - Chemistry LibreTexts View original
Is this image relevant?
Organic Chemistry Reaction Mechanisms for the MCAT - Reactions of Carboxylic Acid Derivatives ... View original
Is this image relevant?
Nucleophilic acyl substitution - Wikipedia View original
Is this image relevant?
22.1: Introduction - Chemistry LibreTexts View original
Is this image relevant?
1 of 3
Top images from around the web for Categories of carboxylic acid reactions
Nucleophilic acyl substitution - Wikipedia View original
Is this image relevant?
22.1: Introduction - Chemistry LibreTexts View original
Is this image relevant?
Organic Chemistry Reaction Mechanisms for the MCAT - Reactions of Carboxylic Acid Derivatives ... View original
Is this image relevant?
Nucleophilic acyl substitution - Wikipedia View original
Is this image relevant?
22.1: Introduction - Chemistry LibreTexts View original
Is this image relevant?
1 of 3
- reactions involve a nucleophile attacking the electrophilic resulting in substitution of the hydroxyl group with the nucleophile (alcohols, amines, ammonia)
- reactions add hydrogen to the carbonyl carbon using reducing agents ( (LiAlH4), (BH3)) forming
- removes the carboxyl group as carbon dioxide (CO2) through heat, enzymatic reactions, or strong acids/bases yielding the corresponding alkane or alkene
- Substitution at the replaces the α-hydrogen with an electrophile facilitated by an intermediate (, )
- reactions form esters by reacting carboxylic acids with alcohols
Reduction to primary alcohols
- Strong reducing agents (lithium aluminum hydride (LiAlH4), borane (BH3)) reduce carboxylic acids to primary alcohols
- LiAlH4 is a powerful hydride donor that reduces the carbonyl group to a primary alcohol in anhydrous ether or (THF) under inert atmosphere
- Mechanism: nucleophilic addition of hydride to the carbonyl carbon followed by protonation during aqueous workup
- Borane (BH3) is a milder reducing agent used in THF
- Resulting intermediate is oxidized using (H2O2) to yield the primary alcohol
- Two-step reduction process:
- Nucleophilic addition of hydride to the carbonyl carbon
- Protonation of the resulting alkoxide ion during aqueous workup
Reactivity vs alcohols and ketones
- Carboxylic acids are more reactive than alcohols and ketones
- Nucleophilic acyl substitution reactivity:
- Carboxylic acids readily undergo substitution due to the electrophilic carbonyl carbon and hydroxyl group being a good leaving group
- Alcohols and ketones are less susceptible due to the absence of a good leaving group
- Acid-base properties:
- Carboxylic acids are weak acids (pKa 4-5) due to the electron-withdrawing carbonyl group stabilizing the conjugate base ()
- Alcohols and ketones are not acidic under normal conditions lacking a strongly electron-withdrawing group
- Reduction:
- Carboxylic acids are reduced to primary alcohols using strong reducing agents (LiAlH4, BH3)
- Ketones are reduced to secondary alcohols using milder reducing agents (sodium borohydride (NaBH4), catalytic hydrogenation)
- Alcohols require conversion to a better leaving group (tosylate, halide) before reduction to hydrocarbons
Carboxylic Acid Derivatives and Reactions
- are formed by the condensation of two carboxylic acid molecules
- The carbonyl group in carboxylic acids is responsible for their reactivity and chemical properties
- Carboxylic acids can undergo reactions to form various products depending on the oxidizing agent used
- The of carboxylic acids is influenced by substituents and structural factors
Key Terms to Review (29)
Acid Anhydrides: Acid anhydrides are organic compounds that contain two acyl groups bonded to a central oxygen atom. They are formed by the dehydration of two carboxylic acid molecules and serve as important intermediates in various chemical reactions, particularly those involving carboxylic acids.
Acidity: Acidity refers to the ability of a substance to donate protons (H+ ions) or the concentration of H+ ions in a solution. It is a fundamental concept in organic chemistry that governs the properties and reactivity of various functional groups, including alcohols, phenols, and carboxylic acids.
Acidity constant, Ka: The acidity constant, Ka, measures the strength of an acid in a solution by quantifying its tendency to donate a proton (H+) to a base. It is expressed as the equilibrium constant for the dissociation of the acid into its conjugate base and a proton in water.
Acyl Chloride: An acyl chloride is a highly reactive organic compound derived from a carboxylic acid, where the hydroxyl (-OH) group has been replaced by a chlorine atom (-Cl). These compounds are widely used in organic synthesis as versatile intermediates for the preparation of various functional groups.
Alkylborane: An alkylborane is an organic compound consisting of a boron atom bonded to one or more alkyl groups. These compounds are important intermediates in organic synthesis, particularly in the hydration of alkynes and the reactions of carboxylic acids.
Borane: Borane is a chemical compound with the formula BH3, consisting of a boron atom bonded to three hydrogen atoms. It is a highly reactive and flammable gas that serves as a key intermediate in organic chemistry, particularly in reactions involving alkenes, alkynes, and carboxylic acids.
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.
Carbonyl group: A carbonyl group is a functional group characterized by a carbon atom double-bonded to an oxygen atom, represented as C=O. This group is pivotal in organic chemistry as it forms the backbone of various important classes of compounds, influencing their chemical properties and reactivity.
Carboxylate Ion: The carboxylate ion is a negatively charged species formed when a carboxylic acid loses a proton (H+). It is a key intermediate in various organic chemistry reactions and plays a crucial role in understanding the structure and properties of carboxylic acids, as well as their reactions and the chemistry of acid anhydrides.
Carboxylic Acids: Carboxylic acids are a class of organic compounds containing a carboxyl functional group (-COOH) attached to an alkyl or aryl group. They are characterized by their acidic properties and play a crucial role in various chemical reactions and biological processes.
Carboxylic acids, RCO2H: Carboxylic acids are organic compounds characterized by the presence of a carboxyl group (-COOH), where "R" represents an alkyl or aryl group attached to the carbon atom of the carboxyl group. They are known for being acidic due to the ability of the hydroxyl (OH) part of the carboxyl group to release a proton (H+).
Decarboxylation: Decarboxylation is a chemical reaction that involves the removal of a carboxyl group (–COOH) from a molecule, typically resulting in the release of carbon dioxide (CO2). This process is important in various organic chemistry reactions and metabolic pathways.
Enolate ion: An enolate ion is a negatively charged intermediate formed from the deprotonation of an alpha carbon adjacent to a carbonyl group in aldehydes and ketones. It plays a crucial role in various organic reactions, including nucleophilic addition and substitution reactions.
Enolate Ion: An enolate ion is a type of conjugate base formed when the alpha hydrogen of a carbonyl compound is removed, resulting in a negatively charged oxygen atom adjacent to a carbon-carbon double bond. This reactive intermediate is a key player in various organic reactions, including conjugate nucleophilic additions, reactions of carboxylic acids, and carbonyl condensation reactions.
Esterification: Esterification is a chemical reaction that involves the formation of an ester compound from the reaction between a carboxylic acid and an alcohol. This process is crucial in various areas of organic chemistry, including the properties of functional groups, polar reactions, the behavior of alcohols and phenols, the reactions of carboxylic acids, the chemistry of esters, and the reactions of monosaccharides.
Fischer Esterification: Fischer esterification is a chemical reaction that involves the formation of an ester compound from a carboxylic acid and an alcohol, typically in the presence of an acid catalyst. This reaction is a key process in the synthesis and interconversion of various organic compounds, particularly esters, which have a wide range of applications in the fields of chemistry, biology, and industry.
Fischer esterification reaction: A Fischer esterification reaction is a chemical process where a carboxylic acid reacts with an alcohol in the presence of an acid catalyst to form an ester and water. It is an equilibrium process that is often driven to completion by removing the water formed during the reaction.
Hell-Volhard-Zelinsky Reaction: The Hell-Volhard-Zelinsky reaction is a method used to selectively brominate the alpha carbon of a carboxylic acid. It involves the use of bromine and phosphorus tribromide to introduce a bromine atom at the carbon adjacent to the carboxylic acid group.
Hydrogen Peroxide: Hydrogen peroxide (H2O2) is a colorless, slightly viscous liquid that is a common oxidizing agent used in a variety of chemical reactions. It is an important compound that plays a role in several organic chemistry topics, including the hydration of alkenes, oxidation of alkenes, hydration of alkynes, preparation of alcohols, and reactions of carboxylic acids.
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.
Nucleophilic Acyl Substitution: Nucleophilic acyl substitution is a type of organic reaction where a nucleophile attacks the carbonyl carbon of a carboxylic acid derivative, such as an acid chloride, anhydride, or ester, leading to the replacement of the leaving group with the nucleophile. This process is central to the reactivity and transformations of carboxylic acid derivatives.
Nucleophilic acyl substitution reaction: A nucleophilic acyl substitution reaction is a type of chemical reaction where a nucleophile replaces the leaving group in an acyl compound. This reaction is fundamental in organic chemistry for modifying carboxylic acid derivatives into other functional groups.
Oxidation: Oxidation is a fundamental chemical process in which a substance loses electrons, resulting in an increase in its oxidation state. This term is central to understanding various reactions and transformations in organic chemistry, from the hydration of alkenes to the oxidation of alcohols and aldehydes.
Primary Alcohols: Primary alcohols are organic compounds with the hydroxyl (-OH) functional group attached to the first (primary) carbon atom of an alkyl chain. These alcohols are important intermediates in various organic reactions, including the preparation of alkyl halides, the oxidation of alcohols, and the synthesis of carboxylic acids.
Reduction: Reduction is a chemical process that involves the gain of electrons by a molecule or atom, resulting in a decrease in its oxidation state. This term is particularly important in the context of various organic chemistry reactions and transformations.
Tetrahydrofuran: Tetrahydrofuran (THF) is a cyclic ether compound with the chemical formula (CH2)4O. It is a colorless, volatile, and flammable liquid that is widely used as a solvent and as a building block in organic synthesis.
Thionyl Chloride: Thionyl chloride (SOCl2) is a highly reactive organic compound commonly used as a reagent in various chemical reactions, particularly in the context of preparing alkyl halides from alcohols, as well as in the reactions and chemistry of carboxylic acids and their derivatives.
α-carbon: The α-carbon is the carbon atom that is directly bonded to a carbonyl group (C=O) in organic compounds. It is a crucial structural feature that plays a significant role in various reactions and transformations involving carbonyl-containing molecules.
α-Halogenation: α-Halogenation is a chemical reaction where a halogen atom (such as chlorine, bromine, or iodine) is introduced onto the α-carbon, which is the carbon atom adjacent to a carbonyl group (a carbon-oxygen double bond). This reaction is particularly relevant in the context of carboxylic acid reactions, the reactivity of enols, and the reactivity of enolate ions.