Carboxylic Acids and Esters Overview

Carboxylic Acids and Esters

• Carboxylic acids have a carboxyl group.
• The carboxyl group can be represented as -C-OH, -COOH, or -CO2H.
• Derivatives of carboxylic acids include anhydrides, esters, and amides.
• These derivatives are formed by reacting a carboxyl acid group with another molecule, resulting in the loss of water.
• Carboxylic acid IUPAC names use the longest carbon chain containing the carboxyl group as the parent alkane.
• The final '-e' in the parent alkane name is changed to '-oic acid'.
• Substituents, such as -OH (hydroxy) and -NH2 (amino), are included in the name.

Naming Carboxylic Acids

• The longest carbon chain containing the carboxyl group is identified as the parent alkane.
• The carboxyl carbon is always numbered 1.
• The name change is from -e of the parent chain to -oic acid.

Dicarboxylic Acids

• The suffix -dioic acid is added to name the parent alkane name.
• Carboxyl acid groups are at the chain ends; hence, no need to number them.

Examples of Carboxylic Acids

• Specific examples of carboxylic acids with their common and IUPAC names, their structures and derivations are listed.

Physical Properties of Carboxylic Acids

• Carboxylic acids contain three polar covalent bonds (C=O, C-O, and O-H).
• The polarity of the carboxyl group dictates physical properties.
• Carboxylic acids have higher boiling points than comparable organic compounds due to hydrogen bonding.
• Carboxylic acids are more soluble in water than alcohols, ethers, aldehydes, and ketones.

Fatty Acids

• Fatty acids are long-chain carboxylic acids.
• Derived from animal fats, vegetable oils, or phospholipids from biological membranes.
• Generally 12-20 carbons in an unbranched chain, often with an even number of carbons
• Can be saturated or unsaturated.
• Unsaturated fatty acids have lower melting points than saturated.
• Cis isomers of unsaturated fatty acids are common; trans isomers are less so.

Reactions of Carboxylic Acids

• Acid-Base Properties: Ionization and reaction with bases, esterification, reduction(using reagents like NaBH4 or LiAlH4). Decarboxylation
• Derivatives of Carboxylic Acids: Reaction with acids (anhydride formation) and with amines (amide formation).

Acidity of Carboxylic Acids

• Carboxylic acids are weak acids.
• Their Ka (acid dissociation constant) typically ranges from 10⁻⁴ to 10⁻⁵ for unsubstituted aliphatic and aromatic carboxylic acids.
• The pKa value indicates the pH at which half of the acid has lost its hydrogen.
• Highly electronegative substituents near the carboxyl group increase the acidity of carboxylic acids. Examples include -OH, -Cl, and -NH3+.

Reaction with Bases

• Carboxylic acids react with strong bases (NaOH, KOH) to form water-soluble salts (e.g., sodium benzoate).
• They also react with weak bases (amines) to form water-soluble salts.
• Acids also react with sodium bicarbonate and sodium carbonate to form water-soluble sodium salts and carbonic acid, which further decomposes to water and carbon dioxide.

Reduction

• Lithium aluminum hydride (LiAlH4) is a common reagent to reduce carboxylic acids to primary alcohols.
• The process is commonly carried out in diethyl ether.

Fischer Esterification

• Fischer esterification is a common method to make esters.
• Carboxylic acid reacts with alcohol in the presence of an acid catalyst (e.g., sulfuric acid).
• The reaction is reversible and can be controlled by altering the reaction conditions for the preferred product.

Soaps

• Natural soaps are made by boiling animal fats (like lard) with sodium hydroxide (saponification).
• Soap molecules in water form spherical clusters called micelles.
• Hydrophobic tails cluster inwards, while hydrophilic heads face the water.
• Soaps act as emulsifying agents, allowing them to clean dirt (grease, oil, and fat stains) removing them when mixed with water.
• Natural soaps form water-insoluble salts in hard water, due to the presence of divalent cations (Ca²⁺, Mg²⁺, Fe³⁺) in hard water.

Detergents

• Synthetic detergents overcome the precipitation problem in hard water by using sulfonic acid group (-SO₃) instead of the carboxyl group (-COOH).
• Calcium, magnesium and iron salts of sulfonic acids are more soluble in water compared to fatty acid salts.
• Synthetic detergents are primarily synthesized from linear alkylbenzene sulfonates (LAS).

This quiz covers the fundamentals of carboxylic acids and esters, including their structures, naming conventions, and derivatives. It provides insight into the IUPAC naming system for carboxylic acids and discusses the characteristics of dicarboxylic acids. Test your knowledge on these important organic compounds!