Carboxylic Acids and Esters

Carboxylic Acids

Their molecules contain the -COOH group.

• HCOOH (formic acid).
• CH₃COOH (acetic acid).
• C₁₇H₃₅COOH (stearic acid).

They are weak acids. They react with metals, basic oxides, alkalis and salts.

• 2CH₃COOH + Zn → (CH₃COO)₂Zn + H₂.
• CH₃COOH + NaOH → CH₃COONa + H₂O.
• Formic acid gives the silver mirror test (it also has aldehyde properties).

Esterification

1. Acid + alcohol
2. H₂SO₄ (cat.), t
3. Ester + H₂O

The reaction is reversible: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O. The ester formed is ethyl acetate.

• Catalyst: concentrated H₂SO₄.
• Formation of water: from the -OH of the acid and the H atom of the alcohol.
• Esters contain the -COO- group. They have fruity smells.

Hydrolysis, Fats and Soap

• Acid hydrolysis: reversible.
• Alkaline hydrolysis: saponification, irreversible.
• Fats: esters of glycerol and higher carboxylic acids.
• Soap: a salt of a higher acid, C₁₇H₃₅COONa.
• Residue of a saturated acid (stearic, palmitic): solid fat. Residue of an unsaturated acid (oleic): liquid fat (vegetable oil).
• Hydrogenation of a liquid fat (H₂, Ni): solid fat, margarine.