Carboxylic Acids and Esters

Quick Notes

• Carboxylic acids (-COOH) are weak acids and react with carbonates to produce CO₂.
• Carboxylic acids react with alcohols to form esters (in the presence of an acid catalyst).
• Esters are commonly used in perfumes, food flavourings, solvents, and plasticisers.
• Vegetable oils and animal fats are esters of propane-1,2,3-triol (glycerol).
• Esters can be hydrolysed in acidic or alkaline conditions to form carboxylic acids (in acidic conditions) or carboxylate salts (in alkaline conditions).
• Alkaline hydrolysis of fats and oils produces soap and glycerol.
• Biodiesel is a mixture of methyl esters of long-chain carboxylic acids, formed by reacting vegetable oils with methanol and a catalyst.

Full Notes

Carboxylic acids contain a carboxyl functional group (-COOH).

Esters (-COOR) are derived from carboxylic acids and alcohols.

Properties and Reactions of Carboxylic Acids

Carboxylic acids are weak acids and can donate H⁺ ions in reactions:

• Partially dissociate in water: CH₃COOH ⇌ CH₃COO⁻ + H⁺
• They can react with carbonates to produce carbon dioxide: 2CH₃COOH + Na₂CO₃ → 2CH₃COO⁻Na⁺ + H₂O + CO₂

Esterification: Formation of Esters

Carboxylic acids react with alcohols in the presence of an acid catalyst (H₂SO₄) to form esters in condensation reactions (water is released).

Reaction:
Carboxylic Acid + Alcohol → Ester + Water

Example:
Ethanoic Acid + Ethanol → Ethyl Ethanoate + Water
CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O

Hydrolysis of Esters

Esters can be broken apart in hydrolysis reactions. The products obtained depend on the conditions used.

Acid Hydrolysis:

• Reagent: Dilute H₂SO₄ or HCl
• Reaction: Ester + Water ⇌ Carboxylic Acid + Alcohol
Example: CH₃COOCH₂CH₃ + H₂O ⇌ CH₃COOH + CH₃CH₂OH

Alkaline Hydrolysis:

• Reagent: NaOH
• Reaction: Ester + NaOH → Carboxylate Salt + Alcohol
Example: CH₃COOCH₂CH₃ + NaOH → CH₃COO⁻Na⁺ + CH₃CH₂OH

Saponification (Soap Formation) and Biodiesel Production

Vegetable oils and animal fats are esters of glycerol (propane-1,2,3-triol).

Alkaline hydrolysis of fats produces soap and glycerol.

Reaction:
Fat/Oil + NaOH → Soap (Carboxylate Salt) + Glycerol

Biodiesel Production:

Biodiesel is a mixture of methyl esters of long chain carboxylic acids and can be used as a fuel for diesel engines.
Can be made by reacting vegetable oils with methanol in the presence of a catalyst to form methyl esters.

Summary

• Carboxylic acids (-COOH) are weak acids that react with carbonates to release CO₂.
• Esterification: carboxylic acid + alcohol ⇌ ester + water (acid catalyst).
• Acid hydrolysis of esters gives a carboxylic acid and an alcohol; alkaline hydrolysis gives a carboxylate salt and an alcohol.
• Fats and oils (triglycerides) are esters of glycerol; alkaline hydrolysis (saponification) produces soap and glycerol.
• Biodiesel is made by converting vegetable oils to methyl esters using methanol and a catalyst.