Ethanoic Acid & Esterification Reactions
Section: 11. Organic Chemistry | Syllabus: Cambridge IGCSE Chemistry (0620)
Formation of Ethanoic Acid by Oxidation of Ethanol (Supplement)
Ethanoic acid can be formed by oxidising ethanol, in two different ways:
- Chemical oxidation: with acidified aqueous potassium manganate(VII) (KMnO₄), which acts as an oxidising agent
- Biological oxidation: by bacteria, during vinegar production - this is how an opened bottle of wine turns sour over time
C₂H₅OH + 2[O] → CH₃COOH + H₂O
The same reaction oxidises any primary alcohol to the corresponding carboxylic acid, e.g. propan-1-ol is oxidised to propanoic acid.
Worked Example
- Question (based on a real exam question): propanoic acid is made by oxidation of an alcohol using KMnO₄. (i) Name the alcohol oxidised to form propanoic acid. (ii) Give the chemical name of KMnO₄. (iii) State the two conditions needed for this oxidation.
- Answer: (i) propan-1-ol; (ii) potassium manganate(VII); (iii) acidified and aqueous.
Esterification (Supplement)
A carboxylic acid reacts with an alcohol, using an acid catalyst, to form an ester and water. The reaction is reversible.
carboxylic acid + alcohol ⇌ ester + water
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
(ethanoic acid + ethanol ⇌ ethyl ethanoate + water)
Esters are named in two parts: the alcohol gives the first part (with the ending "-yl"), and the acid gives the second part (with the ending "-oate"), e.g. ethanol + ethanoic acid → ethyl ethanoate.
Esters are volatile, insoluble in water, and often have sweet, fruity smells - they are used as flavourings and in perfumes.
Worked Example
- Question (based on a real exam question): butanoic acid reacts with ethanol to form an ester, using an acid catalyst. (i) State the type of catalyst needed. (ii) Complete the word equation: butanoic acid + ethanol ⇌ ____ + ____.
- Answer: (i) an acid catalyst; (ii) ethyl butanoate + water. The alcohol (ethanol) gives "ethyl"; the acid (butanoic acid) gives "butanoate".
Common Mistakes
- ❌ Naming the ester with the acid part first, e.g. calling the product of ethanoic acid + ethanol "ethanoyl ethanol"
- ✓ the alcohol's alkyl name always comes first ("ethyl"), followed by the acid's "-oate" name ("ethanoate") - so ethanoic acid + ethanol gives ethyl ethanoate, not the other way round
- ❌ Forgetting that oxidising an alcohol produces the carboxylic acid with the same number of carbon atoms
- ✓ propan-1-ol (3 carbons) oxidises to propanoic acid (3 carbons) - the carbon chain length does not change, only the end group (-OH becomes -COOH)
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