ChemistryChapter 8: Organic Chemistry
8.3 Esters
**Esters:** Esters are organic compounds that are derived from **carboxylic acids** and alcohols
Explanation level
Introduction
Esters are a family of organic compounds that are widely used in everyday life — from the pleasant smells of fruits and perfumes to the flavours in food and the plastics in our clothes. They are formed from carboxylic acids and alcohols.
This section explains what esters are, how they are formed, and how they are named.
Definition
Esters: Esters are organic compounds that are derived from carboxylic acids and alcohols.
In simple words: An ester is a compound formed when a carboxylic acid reacts with an alcohol.
Main Idea
- Carboxylic acids contain the -COOH group (carboxyl group) and can be represented by the general formula RCOOH.
- When the OH of the carboxyl group is replaced by an OR group from an alcohol, an ester is formed.
- Esters have the general formula RCOOR'.
- The reaction is carried out in the presence of a few drops of dilute sulphuric acid as a catalyst.
- This reaction is known as the esterification reaction.
- Esters possess a fruity odour.
- Both R and R' may be the same or different.
Core Concept
| Feature | Description |
|---|---|
| General formula | RCOOR' |
| Formed from | Carboxylic acid + Alcohol |
| Catalyst | Dilute sulphuric acid |
| Reaction name | Esterification |
| Odour | Fruity |
| Naming | Two parts: alkyl group (from alcohol) + carboxylate (from acid) |
Key point: Esters are formed by the reaction of a carboxylic acid with an alcohol, with a fruity odour.
Detailed Explanation
What are Esters?
Esters are organic compounds that are derived from carboxylic acids and alcohols.
- Carboxylic acids contain the -COOH group (carboxyl group) and can be represented by the general formula RCOOH.
- When the OH of the carboxyl group is replaced by an OR group from an alcohol, an ester is formed.
- It has the general formula RCOOR'.
- The reaction is carried out in the presence of a few drops of dilute sulphuric acid as a catalyst.
- This reaction is known as the esterification reaction.
- Esters possess a fruity odour.
- Both R and R' may be the same or different.
Key point: Esters are formed by the reaction of a carboxylic acid with an alcohol, with a fruity odour.
The Esterification Reaction
General equation:
RCOOH + R'OH → RCOOR' + H2O
Example:
CH3COOH + CH3OH → CH3COOCH3 + H2O
Names of the reactants and products:
| Reactant/Product | Name |
|---|---|
| CH3COOH | Ethanoic acid |
| CH3OH | Methanol |
| CH3COOCH3 | Methyl ethanoate |
| H2O | Water |
Key point: The reaction between a carboxylic acid and an alcohol produces an ester and water.
Naming Esters
Esters have two parts in their names, which reflect the two molecules from which they are formed.
The first part indicates the attached alkyl group from the alcohol.
The second part is the name of the carboxylic acid, with -ic acid replaced by -ate.
For example:
Methyl ethanoate:
- Methyl comes from the methyl group of the parent methyl alcohol.
- Ethanoate is obtained by replacing the -ic acid of the parent ethanoic acid with -ate.
Key point: The name of an ester has two parts: the alkyl group from the alcohol and the carboxylate from the acid.
Examples of Esters
| Carboxylic Acid | Alcohol | Ester | Name |
|---|---|---|---|
| HCOOH (Methanoic acid) | CH3OH (Methanol) | HCOOCH3 | Methyl methanoate |
| CH3COOH (Ethanoic acid) | CH3OH (Methanol) | CH3COOCH3 | Methyl ethanoate |
| CH3COOH (Ethanoic acid) | C2H5OH (Ethanol) | CH3COOC2H5 | Ethyl ethanoate |
| CH3CH2COOH (Propanoic acid) | CH3OH (Methanol) | CH3CH2COOCH3 | Methyl propanoate |
| CH3CH2COOH (Propanoic acid) | C2H5OH (Ethanol) | CH3CH2COOC2H5 | Ethyl propanoate |
Key point: The name of the ester is determined by the alcohol and the carboxylic acid used to form it.
Summary Table
| Feature | Description |
|---|---|
| General formula | RCOOR' |
| Formed from | Carboxylic acid + Alcohol |
| Catalyst | Dilute sulphuric acid |
| Reaction name | Esterification |
| Odour | Fruity |
| Naming | Alkyl group (from alcohol) + carboxylate (from acid) |
| Example | CH3COOH + CH3OH → CH3COOCH3 + H2O (Methyl ethanoate) |
Intermediate Level
Esterification reaction:
RCOOH + R'OH → RCOOR' + H2O
Catalyst: Dilute sulphuric acid
Naming esters:
- Identify the alcohol part → alkyl group name (e.g., methyl, ethyl).
- Identify the acid part → replace "-ic acid" with "-ate" (e.g., ethanoate, propanoate).
- Combine the two parts (e.g., methyl ethanoate, ethyl propanoate).
Examples:
| Alcohol | Acid | Ester |
|---|---|---|
| Methanol | Ethanoic acid | Methyl ethanoate |
| Ethanol | Ethanoic acid | Ethyl ethanoate |
| Methanol | Propanoic acid | Methyl propanoate |
| Ethanol | Propanoic acid | Ethyl propanoate |
Key point: The name of an ester has two parts: the alkyl group from the alcohol and the carboxylate from the acid.
Solved Example
Example: Name the Ester Formed from Ethanoic Acid and Methanol
Question: Name the ester formed from ethanoic acid (CH3COOH) and methanol (CH3OH).
Solution:
Step 1: Identify the alcohol part.
- Alcohol: Methanol → alkyl group: Methyl
Step 2: Identify the acid part.
- Acid: Ethanoic acid → replace "-ic acid" with "-ate" → Ethanoate
Step 3: Combine the two parts.
- Name: Methyl ethanoate
Final Answer: The ester is methyl ethanoate.
Example: Write the Equation for the Formation of Ethyl Ethanoate
Question: Write the equation for the formation of ethyl ethanoate.
Solution:
Reactants:
- Carboxylic acid: Ethanoic acid (CH3COOH)
- Alcohol: Ethanol (C2H5OH)
Equation:
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
Final Answer: The equation is:
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
Concept Assessment Exercise 8.5 (Part 1)
Write the name, displayed and structural formulae of a carboxylic acid containing 4-carbon atoms.
Answer:
- Name: Butanoic acid
- Condensed structural formula: CH3CH2CH2COOH
Concept Assessment Exercise 8.5 (Part 2)
Identify the class of each of the following compounds from their names. Also, write their displayed structural formulas and condensed structural formulas: Pent-2-ol, Pentanoic acid, Pent-2-ene, Pentane.
Answer:
- Class: Alcohol
- Condensed formula: CH3 - CH(OH) - CH2 - CH2 - CH3
- Class: Carboxylic acid
- Condensed formula: CH3 - CH2 - CH2 - CH2 - COOH
- Class: Alkene
- Condensed formula: CH3 - CH = CH - CH2 - CH3
- Class: Alkane
- Condensed formula: CH3 - CH2 - CH2 - CH2 - CH3
Important Points
- - Esters = organic compounds derived from carboxylic acids and alcohols.
- - General formula: RCOOR'.
- - Formed from: Carboxylic acid + Alcohol.
- - Catalyst: Dilute sulphuric acid.
- - Reaction name: Esterification.
- - Odour: Fruity.
- - Naming: Two parts — alkyl group (from alcohol) + carboxylate (from acid).
- - Example: CH3COOH + CH3OH → CH3COOCH3 + H2O (Methyl ethanoate).
- - Both R and R' may be the same or different.
Remember
- - Esters = carboxylic acid + alcohol.
- - General formula: RCOOR'.
- - Catalyst: Dilute sulphuric acid.
- - Reaction: Esterification.
- - Odour: Fruity.
- - Naming: Alkyl group + carboxylate.
- - Example:
- - Methanol + Ethanoic acid → Methyl ethanoate
- - Ethanol + Ethanoic acid → Ethyl ethanoate
- - Methanol + Propanoic acid → Methyl propanoate
- - Both R and R' may be the same or different.
Common Mistakes
| Mistake | Correction |
|---|---|
| Thinking esters are formed from carboxylic acids and water | Esters are formed from carboxylic acids and alcohols |
| Forgetting the catalyst | Dilute sulphuric acid is used as a catalyst |
| Confusing the name parts | First part = alkyl group (from alcohol); second part = carboxylate (from acid) |
| Forgetting to replace "-ic acid" with "-ate" | For example, ethanoic acid → ethanoate |
| Thinking all esters have the same smell | Esters have different fruity odours |
| Confusing esters with carboxylic acids | Esters: -ate; Carboxylic acids: -oic acid |
| Thinking R and R' must be the same | R and R' may be the same or different |
Quick Revision
Esters:
Esters are organic compounds that are derived from carboxylic acids and alcohols. Carboxylic acids contain -COOH group (carboxylic group) and can be represented by the general formula RCOOH. When OH of the carboxyl group is simply replaced by OR group from an alcohol an ester is formed. It has a general formula RCOOR. The reaction is carried out in the presence of a few drops of dilute sulphuric acid as a catalyst. This reaction is known as esterification reaction. Esters possess a fruity odour. Both R and R may be the same or different.
- RCOOH + ROH → RCOOR + H2O
- CH3COOH + CH3OH → CH3COOCH3 + H2O
Ethanoic acid + Methanol → Methyl Ethanoate + Water
Their names have two parts, which reflect these two molecules. The first part indicates the attached alkyl group from alcohol and the second one is the name of carboxylic acid, the -ic acid is replaced with -ate. For example, methyl ethanoate gets its name from the methyl group of the parent methyl alcohol, while ethanoate is obtained by replacing the -ic acid of parent ethanoic acid with -ate.
Examples:
| Carboxylic Acid | Alcohol | Ester |
|---|---|---|
| Methanoic acid | Methanol | Methyl methanoate |
| Ethanoic acid | Methanol | Methyl ethanoate |
| Ethanoic acid | Ethanol | Ethyl ethanoate |
| Propanoic acid | Methanol | Methyl propanoate |
| Propanoic acid | Ethanol | Ethyl propanoate |
60-Second Revision
- Esters = carboxylic acid + alcohol.
- General formula: RCOOR'.
- Catalyst: Dilute sulphuric acid.
- Reaction: Esterification.
- Odour: Fruity.
- Naming: Alkyl group + carboxylate.
- Example:
- Methanol + Ethanoic acid → Methyl ethanoate
- Ethanol + Ethanoic acid → Ethyl ethanoate
- Methanol + Propanoic acid → Methyl propanoate
- Both R and R' may be the same or different.
- Reaction: RCOOH + R'OH → RCOOR' + H2O.
- ⚠️ Warning: the name of an ester has two parts — the alkyl group from the alcohol and the carboxylate from the acid.
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Review the key facts, formulas and checks before you move on.8.3 Esters
Sticky Notes · Quick Revision
Key Point 1
- Esters = carboxylic acid + alcohol.
Key Point 2
- General formula: RCOOR'.
Key Point 3
- Catalyst: Dilute sulphuric acid.
Key Point 4
- Reaction: Esterification.
Key Point 5
- Odour: Fruity.
Key Point 6
- Naming: Alkyl group + carboxylate.
Key Point 7
- Example:
Key Point 8
- Methanol + Ethanoic acid → Methyl ethanoate
Key Point 9
- Ethanol + Ethanoic acid → Ethyl ethanoate
Key Point 10
- Methanol + Propanoic acid → Methyl propanoate
Key Point 11
- Both R and R' may be the same or different.
Key Point 12
- Reaction: RCOOH + R'OH → RCOOR' + H2O.
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