Carboxylic Acids and Derivatives

Solubility in Water

• Smaller carboxylic acids (up to C4) dissolve in water due to hydrogen bonding.
• Larger carboxylic acids have reduced solubility.

Acidity

• Carboxylic acids are weak acids that slightly dissociate in water.
• They can displace CO2 from carbonates.
• Salts are stabilized by delocalization, making dissociation more likely.
• Delocalization results in equal C-O bond lengths, enhancing stability.

Strength of Carboxylic Acids

• Increased chain length decreases acid strength due to electron density push onto COO- ion.
• Alkyl groups are electron-releasing, making acids less strong.
• Chlorine is electron-withdrawing, increasing acidity.
• Propanoic acid < ethanoic acid; Chloroethanoic acid > ethanoic acid.

Naming Carboxylic Acids

• End with '-oic acid'; no numbering needed as the acid group is at the chain end.
• Numbering starts from the carboxylic acid end.
• Dioic acids have carboxylic groups on both ends.

Esterification

• Carboxylic acids react with alcohols to form esters and water using a strong acid catalyst.
• Reaction is reversible and slow, requiring heating under reflux and acid catalyst (H2SO4).
• Esters are sweet-smelling and used in perfumes and as solvents.
• Not hydrogen-bonded, having lower boiling points than carboxylic acids.

Oxidation of Methanoic Acid

• Carboxylic acids can't be oxidized, but methanoic acid can due to its aldehyde group.
• Results in carbonic acid, decomposing to CO2.

Salt Formation Reactions

• Carboxylic acids form salts with metals, alkalis, and carbonates.
• Effervescence from CO2 production is a test for carboxylic acids.

Hydrolysis of Esters

• Esters hydrolyzed by heating with acid or sodium hydroxide.
• Acid hydrolysis is reversible; sodium hydroxide hydrolysis goes to completion.
• Practical methods involve heating under reflux.

Uses of Esters

• Esters are used as perfumes, flavourings, solvents, and plasticisers.
• They allow grease and water to mix and be washed away.

Biodiesel

• Produced from vegetable oils by reacting with methanol.
• Considered carbon neutral if energy inputs are renewable.

Carboxylic Acid Derivatives

Acyl Chlorides and Acid Anhydrides

• Both are more reactive than carboxylic acids and esters.
• Acyl chlorides release HCl, while acid anhydrides release RCOOH.

Reactions with Water and Alcohols

• Acyl chlorides and acid anhydrides form carboxylic acids with water.
• They form esters with alcohols, with acyl chlorides producing HCl.

Reactions with Ammonia and Amines

• Form primary amides with ammonia.
• Form secondary amides with primary amines.

Purifying an Organic Solid: Recrystallisation

• Process involves dissolving in hot solvent, filtering, cooling, and recrystallization.
• Crystal purity is tested by melting point determination.
• Buchner flask used for purification.

Practical: Making Aspirin

• Made from 2-hydroxybenzoic acid using ethanoic anhydride.
• Ethanoic anhydride is preferred over acid chlorides due to safety and cost.

Measuring Melting Point

• Used to determine purity by comparing with data books.
• Impurities lower melting point and broaden the range.