4.8.3Unit 4. Rates, Equilibria and Further Organic Chemistry
Reactions of Carboxylic Acids — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 4 parts Lesson 47 of 56 Unit quiz
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Section 1 of 4Acid Reactions
Carboxylic acids are weak acids but show typical acid reactions with metals, bases and carbonates.
With metals
- With metals 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂, so magnesium dissolves with effervescence.
With bases
- With bases CH₃COOH + NaOH → CH₃COONa + H₂O, forming a carboxylate salt and water.
With carbonates
- With carbonates 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂, giving fizzing, which is a test for the acid group.
Salt name
- Salt name The salt formed is a carboxylate, such as sodium ethanoate, with the ending -oate.
Test for acids
- Test for acids Fizzing with sodium hydrogencarbonate solution distinguishes a carboxylic acid from most alcohols, which do not react with carbonates.
Section 2 of 4Other Reactions
Other Reactions
Esterification
- Esterification An acid and an alcohol heated with concentrated H₂SO₄ catalyst form an ester and water in a reversible reaction.
Reduction
- Reduction LiAlH₄ in dry ether reduces carboxylic acids to primary alcohols: CH₃COOH + 4[H] → CH₃CH₂OH + H₂O.
Acyl chloride formation
- Acyl chloride formation PCl₅ reacts at room temperature: CH₃COOH + PCl₅ → CH₃COCl + POCl₃ + HCl.
Strength
- Strength NaBH₄ cannot reduce carboxylic acids, so a stronger reducing agent is required.
Section 3 of 4Esterification in Detail
1
Mix the carboxylic acid and the alcohol with a few drops of concentrated sulfuric acid as a catalyst.
2
Heat the mixture under reflux, because the reaction is slow and the reagents are volatile.
3
The reaction reaches equilibrium: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O.
4
Distil off the ester, which has a lower boiling point than the acid, and wash it with sodium carbonate solution.
Section 4 of 4Exam Checklist & Tips
4.8.3 – Key Points for the Exam
- Carboxylate The anion RCOO⁻ or its salt.
- Esterification Reaction of an acid and an alcohol to form an ester.
- Reflux Heating with continuous condensation of vapours.
- Effervescence Fizzing caused by gas release.
Common Mistakes
- Writing a carbonate reaction without CO₂ and water.
- Using NaBH₄ to reduce a carboxylic acid.
- Forgetting the sulfuric acid catalyst in esterification.
- Giving the salt the ending -ate rather than -oate.
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