Chemical Properties of Ethyl Ethanoate

Overview of Ester Reactivity

Esters like ethyl ethanoate are relatively unreactive compared to other organic compounds. They do not react with most common reagents at room temperature. However, they undergo specific reactions under certain conditions.

The key to understanding ester reactions is the ester link (C-O-C with a C=O next to it). This is the weak point in the molecule where most reactions occur. Think of it as a bridge that can be broken and rebuilt in different ways.

Most reactions of ethyl ethanoate involve breaking this ester link. When the link breaks, you get back compounds similar to the original alcohol and acid used to make the ester.

1. Hydrolysis of Ethyl Ethanoate

Hydrolysis means “breaking with water.” This is the reverse of esterification. When you add water to ethyl ethanoate under proper conditions, it breaks down into ethanol and ethanoic acid.

Acid Hydrolysis

In acid hydrolysis, you heat the ester with dilute acid (usually dilute HCl or dilute H₂SO₄) and water. The reaction is slow and reversible.

Equation:

CH₃COOC₂H₅₍ₗ₎ + H₂O₍ₗ₎ ⇌ CH₃COOH₍ₗ₎ + C₂H₅OH₍ₐq₎
Ethyl ethanoate + Water ⇌ Ethanoic acid + Ethanol

Conditions:

• Dilute acid (HCl or H₂SO₄) as catalyst
• Heat under reflux
• Reaction is reversible (double arrow ⇌)
• Slow reaction – may take several hours

The dilute acid speeds up the reaction but does not change the equilibrium position. Since the reaction is reversible, you get a mixture of ester, water, acid, and alcohol at equilibrium.

Alkaline Hydrolysis (Saponification)

Alkaline hydrolysis uses a base like sodium hydroxide (NaOH) instead of acid. This reaction is faster and goes to completion (not reversible).

Equation:

CH₃COOC₂H₅₍ₗ₎ + NaOH₍ₐq₎ → CH₃COONa₍ₐq₎ + C₂H₅OH₍ₗ₎
Ethyl ethanoate + Sodium hydroxide → Sodium ethanoate + Ethanol

Conditions:

• Sodium hydroxide solution (or potassium hydroxide)
• Heat gently
• Reaction is irreversible (single arrow →)
• Much faster than acid hydrolysis

This reaction is called saponification because it is similar to soap making. Instead of getting the carboxylic acid (ethanoic acid), you get its salt (sodium ethanoate). The reaction is irreversible because the base neutralizes the acid as it forms.

Comparison: Acid vs Alkaline Hydrolysis

2. Reduction of Ethyl Ethanoate

Reduction means adding hydrogen to a compound. Ethyl ethanoate can be reduced to ethanol using very strong reducing agents.

Equation:

CH₃COOC₂H₅₍ₗ₎ + 4[H] → 2C₂H₅OH₍ₗ₎
Ethyl ethanoate + Hydrogen → Ethanol

Reducing agents used:

• Lithium tetrahydridoaluminate(III) – LiAlH₄ (most common in exams)
• Lithium aluminum hydride (another name for the same compound)
• Sodium tetrahydridoborate – NaBH₄ (less commonly used)

Conditions:

• Use dry ether as solvent
• Perform under anhydrous (no water) conditions
• LiAlH₄ reacts violently with water, so keep everything dry

Important points:

1. The [H] in the equation represents hydrogen from the reducing agent, not H₂ gas
2. Both parts of the ester (acid part and alcohol part) are reduced to ethanol
3. You get 2 molecules of ethanol from 1 molecule of ester
4. This is a very strong reduction – mild reducing agents will not work

Think of this reaction as breaking the ester and converting both pieces into the same alcohol. The acetyl part (CH₃CO-) gets reduced to ethyl (C₂H₅-), which combines with -OH to form another ethanol molecule.

3. Reaction with Ammonia

When ethyl ethanoate reacts with ammonia gas, it forms ethanamide (an amide) and ethanol.

Equation:

CH₃COOC₂H₅₍ₗ₎ + NH₃₍g₎ → C₂H₅OH₍ₗ₎ + CH₃CONH₂₍s₎
Ethyl ethanoate + Ammonia → Ethanol + Ethanamide

Conditions:

• Pass dry ammonia gas through the ester
• Gentle heating may speed up the reaction
• Can also use concentrated ammonia solution

Explanation:

This reaction is similar to hydrolysis, but ammonia (NH₃) replaces water (H₂O). Instead of getting the acid back, you get an amide. An amide is like an acid but with -NH₂ replacing the -OH group.

The ethyl part of the ester is released as ethanol, just like in hydrolysis. The acetyl part combines with ammonia to form ethanamide (CH₃CONH₂), which is a white solid.

4. Reaction with Grignard Reagents

Although not frequently asked in WAEC exams, esters react with Grignard reagents (organometallic compounds) to form tertiary alcohols. This is advanced organic chemistry covered briefly.

Grignard reagents have the general formula RMgX (where R is an alkyl group, X is a halogen). They are extremely reactive and must be used in dry conditions.

5. What Ethyl Ethanoate Does NOT Do

Understanding what esters cannot do helps in exams:

• Does not reduce Fehling’s solution: Esters have no free aldehyde or ketone group, so they don’t give a brick-red precipitate with Fehling’s solution
• Does not reduce Tollen’s reagent: No silver mirror forms because esters cannot be oxidized easily
• Does not react with sodium metal: Esters have no -OH group, so they don’t release hydrogen with sodium like alcohols do
• Does not decolorize bromine water easily: Esters are saturated (no C=C double bonds in simple esters like ethyl ethanoate)
• Does not affect litmus paper: Esters are neutral, unlike carboxylic acids (acidic) or amines (basic)

These negative tests help distinguish esters from aldehydes, ketones, alcohols, and acids in practical chemistry exams.

Summary Table of Reactions

Common Exam Mistakes

WAEC Chief Examiners note these frequent errors in questions on ester reactions:

1. Confusing acid and alkaline hydrolysis products: Students write ethanoic acid as the product of alkaline hydrolysis. Remember: alkaline hydrolysis gives the SALT (sodium ethanoate), not the acid.
2. Wrong arrow direction: Using single arrow (→) for acid hydrolysis instead of double arrow (⇌). Acid hydrolysis is reversible, alkaline hydrolysis is not.
3. Forgetting the coefficient in reduction: The equation needs 4[H], not just [H]. Also, the product is 2 molecules of ethanol, not 1.
4. Writing wrong product formulas: Common mistakes:
   – Writing C₂H₆OH instead of C₂H₅OH for ethanol
   – Writing CH₃CONH instead of CH₃CONH₂ for ethanamide
   – Missing the sodium in sodium ethanoate
5. Confusing saponification with neutralization: Saponification is ester + base → salt + alcohol. Neutralization is acid + base → salt + water. Different reactions!
6. Stating esters reduce Fehling’s solution: Esters do NOT reduce Fehling’s solution. Only aldehydes and some ketones do. This is a common trap in multiple choice questions.
7. Not specifying conditions: When asked to describe a reaction, always mention:
   – The reagent used
   – Temperature/heating requirements
   – Whether it’s reversible
   – The catalyst (if any)
8. Poor equation balancing: Some students add random coefficients. Check: atoms on left = atoms on right.
9. Explaining instead of stating: When asked to “state” products, just list them. When asked to “explain,” give the mechanism or conditions too.

Practice Questions

Multiple Choice Questions

1. Alkaline hydrolysis of ethyl ethanoate produces:

• Ethanoic acid and ethanol
• Sodium ethanoate and ethanol ✓
• Ethanol and ethanamide
• Two molecules of ethanol

2. Which reducing agent is used to reduce ethyl ethanoate to ethanol?

• Hydrogen gas with nickel catalyst
• Fehling’s solution
• Lithium tetrahydridoaluminate(III) ✓
• Dilute sulfuric acid

3. The reaction between ethyl ethanoate and sodium hydroxide is called:

• Neutralization
• Esterification
• Saponification ✓
• Polymerization

4. When ethyl ethanoate reacts with ammonia, one of the products formed is:

• Ethanoic acid
• Ethanamide ✓
• Ethylamine
• Ammonium ethanoate

5. Which statement about acid hydrolysis of esters is correct?

• It is faster than alkaline hydrolysis
• It is an irreversible reaction
• It produces a carboxylic acid and an alcohol ✓
• It requires concentrated sulfuric acid

Essay/Theory Questions

1. (a) Write a balanced equation for the hydrolysis of ethyl ethanoate using dilute sulfuric acid. (3 marks)
(b) State two differences between acid hydrolysis and alkaline hydrolysis of esters. (4 marks)
(c) Why is alkaline hydrolysis called saponification? (2 marks)

Examiner’s tip: In (a), use the reversible arrow (⇌). In (b), compare speed, reversibility, and products. In (c), mention that it’s the same process used to make soap from fats.

2. (a) State what would be observed when ethyl ethanoate is treated with:
(i) Sodium metal (1 mark)
(ii) Fehling’s solution (1 mark)
(iii) Sodium hydroxide solution on warming (2 marks)
(b) Write equations for any reactions that occur in 2(a) above. (4 marks)

Examiner’s tip: For (i) and (ii), state “no reaction” – these are negative tests. For (iii), describe the products formed and mention the fruity smell disappearing.

3. (a) Ethyl ethanoate can be reduced to ethanol using lithium tetrahydridoaluminate(III). Write the equation for this reaction. (3 marks)
(b) Explain why two molecules of ethanol are produced from one molecule of ethyl ethanoate. (3 marks)
(c) State two precautions necessary when using LiAlH₄. (2 marks)

Examiner’s tip: In (a), remember the coefficient 4[H] and product 2C₂H₅OH. In (b), explain that both the acid part and alcohol part of the ester are reduced to ethanol. In (c), mention anhydrous conditions and using dry ether solvent.

4. An organic compound X with molecular formula C₄H₈O₂ does not reduce Fehling’s solution. When X is heated with sodium hydroxide solution, compound Y and ethanol are produced.
(a) Identify compound X. (1 mark)
(b) Name the type of reaction that occurred. (1 mark)
(c) Write the structural formula of compound Y. (2 marks)
(d) Write a balanced equation for the reaction. (3 marks)

Examiner’s tip: X is ethyl ethanoate (the molecular formula and negative Fehling’s test confirm it’s an ester). Y is sodium ethanoate. This is saponification.

Memory Aids

For hydrolysis products:
“Acid Makes Acid, Alkali Makes sAlt”
– Acid hydrolysis → carboxylic Acid + alcohol
– Alkaline hydrolysis → sAlt + alcohol

For saponification:
“Soap Needs Strong Alkali” (SNSA)
Saponification = ester + NaOH → Salt + Alcohol

For reduction equation:
“Four H’s make Two E’s”
4[H] produces 2 ethanol molecules (2 “E’s”)

For ammonia reaction:
“Ammonia Attacks, Amide Appears”
NH₃ reacts with ester to form amide (CH₃CONH₂)

For negative tests:
“Esters Escape Fehling’s, Tollen’s, and Sodium Tests”
Remember: esters don’t react with these reagents

Related Topics

To fully understand chemical properties of ethyl ethanoate, study these related posts:

• Ethyl Ethanoate – Structure, preparation, and basic properties
• Physical Properties of Ethyl Ethanoate – Boiling point, solubility, and physical characteristics
• Uses of Esters – Applications in industry and daily life
• Ethanol – One of the key products from ester reactions
• Chemical Properties of Ethanol – How ethanol reacts