9701 · 33.1
Carboxylic acids
Carboxylic acids contain the –COOH group, making them acidic and able to form strong hydrogen bonds. These properties dictate their unique physical characteristics and chemical reactivity.
Need to know
What you need to know
- **Reaction with reactive metals:** They react with metals above hydrogen in the reactivity series (e.g., Mg, Zn) to produce a salt and hydrogen gas. `2RCOOH + Mg \rightarrow (RCOO)_2Mg + H_2`
- **Neutralisation with bases:** They react with bases (e.g., NaOH) and metal oxides (e.g., CuO) in a neutralisation reaction to form a salt and water. `RCOOH + NaOH \rightarrow RCOONa + H_2O`
- **Reaction with carbonates:** They react with carbonates (e.g., `Na_2CO_3`) and hydrogencarbonates (e.g., `NaHCO_3`) to produce a salt, water, and carbon dioxide gas. The effervescence produced is the definitive test for a carboxylic acid, as weaker acids like phenol do not react with `NaHCO_3`.
Explanation
Carboxylic Acids: From Vinegar to Synthesis
- –COOH: dimer H-bonds, higher bp than similar alcohol. | Sim hint: Weak acid — partial dissociation.
- With carbonates: CO₂ evolved — test for acid. | Sim hint: RCOOH + Na₂CO₃ → salt + CO₂ + H₂O.
- Reduction with LiAlH₄ gives primary alcohol. | Sim hint: Not with NaBH₄ for acids at AS.
- Acyl chloride route for esters and amides. | Sim hint: More reactive than acid itself.