AS Level Chemistry 9701

18. Carboxylic acids and derivatives

Written by: Pranav I
Formatted by: Pranav I

Index

18.1 Carboxylic acids

Reactions to make carboxylic acids

#	Reagent	Acts on	Reaction type	Conditions	Example
1	K₂Cr₂O₇	Primary Alcohols	Oxidation	Acidified & heat under reflux	\[ \text{CH}_3\text{CH}_2\text{OH} + [O] \rightarrow \text{CH}_3\text{COOH} + \text{H}_2\text{O} \]
2	KMnO₄	Primary Alcohols	Oxidation	Acidified	\[ \text{CH}_3\text{CH}_2\text{OH} + [O] \rightarrow \text{CH}_3\text{COOH} + \text{H}_2\text{O} \]
3	HCl	Nitriles	Hydrolysis	Dilute & heat under reflux	\[ \text{R-CN} + 2\text{H}_2\text{O} + \text{HCl} \rightarrow \text{R-COOH} + \text{NH}_4\text{Cl} \]

Reacting as typical acids

Weak acids → molecules do not completely dissociate when dissolved in water

\[
\text{CH}_3\text{COOH} + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{COO}^- + \text{H}_3\text{O}^+
\]

Reagent: alkali
Type: neutralization

\[
\text{CH}_3\text{COOH} + \text{NaOH} \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O}
\]

Reagent: reactive metals (e.g. Na)

\[
2\text{CH}_3\text{COOH} + 2\text{Na} \rightarrow 2\text{CH}_3\text{COONa} + \text{H}_2
\]

Reagent: metal carbonates

\[
2\text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \rightarrow 2\text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2
\]

Reduction of carboxylic acids

Reagent: LiAlH₄
Conditions: dry ether

\[
\text{CH}_3\text{COOH} + 4[H] \rightarrow{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{OH} + \text{H}_2\text{O}
\]

🚨 LiAlH4 is a strong reducing agent, so it must not come into contact with water

18.2 Esters

Esterification

Reagent: carboxylic acid
Conditions: concentrated H₂SO₄ catalyst
The -OH bond breaks in this condensation reaction

\[
\text{CH}_3\text{COOH} + \text{C}_3\text{H}_7\text{OH} \rightarrow{\text{H}_2\text{SO}_4} \text{CH}_3\text{COOC}_3\text{H}_7 + \text{H}_2\text{O}
\]

🔥 Naming an ester compound

General form: alkyl alkanoate
- Alkyl → from the alcohol
- Alkonoate → from the carboxylic acid
Examples
- Pentanoic acid + Methanol → Methyl pentanoate + Water
- Methanoic acid + Pentanol → Pentyl methanoate + water

Hydrolysis of esters

Reagent: water or alkali
Conditions: heat under reflux (+ acid, in case of water as the reagent)
Refluxing with an acid reverses the esterification
- Reversible reaction → produces an equilibrium mixture

\[
\text{CH}_3\text{COOCH}_2\text{CH}_3 + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{COOH} + \text{CH}_3\text{CH}_2\text{OH}
\]

Refluxing with an alkali is NOT a reversible reaction
- The ester is fully hydrolyzed
- A metal alkanoate is produced instead of a carboxylic acid

\[
\text{CH}_3\text{COOCH}_2\text{CH}_3 + \text{NaOH} \rightarrow \text{CH}_3\text{COONa} + \text{CH}_3\text{CH}_2\text{OH}
\]