11.1 Carboxylic Acids

Introduction

Carboxylic acids are an important family of organic compounds that contain the carboxyl group (-COOH). They are widely found in nature and are used in many everyday products — from vinegar and citrus fruits to soaps, medicines, and plastics.

The name carboxylic acid comes from the combination of carbonyl (C=O) and hydroxyl (-OH) groups. The carboxyl group shows the chemistry of both of these groups.

This section explains what carboxylic acids are, how they are formed, and their general properties.

Definition

Carboxylic Acids: Carboxylic acids are organic compounds that contain the carboxyl group (-COOH) attached to a hydrocarbon chain.

General Formula: RCOOH

Where:

• R = a hydrocarbon chain (alkyl group)
• -COOH = the carboxyl group

In simple words: Carboxylic acids are organic acids that contain the -COOH group.

Main Idea

• Carboxylic acids contain the carboxyl group (-COOH).
• The carboxyl group is made up of a carbonyl group (C=O) and a hydroxyl group (-OH).
• The carboxyl group shows the chemistry of both the carbonyl and the hydroxyl groups.
• In most reactions, the carboxyl group is retained.
• The reactivity of carboxylic acids is due to the presence of the carbonyl group.
• Carboxylic acids are weaker acids than mineral acids.
• They produce H⁺ ions when dissolved in water.

Core Concept

Key point: Carboxylic acids contain the -COOH group, which is made up of a carbonyl group and a hydroxyl group. They are weaker acids than mineral acids.

Detailed Explanation

What are Carboxylic Acids?

Carboxylic acids are organic compounds that contain the carboxyl group (-COOH) attached to a hydrocarbon chain.

The carboxyl group (-COOH) is made up of:

• A **carbonyl group** (C=O)
• A hydroxyl group (-OH)

Key point: The carboxyl group is a combination of a carbonyl group and a hydroxyl group.

How Carboxylic Acids are Formed

Carboxylic acids can be formed by the oxidation of alcohols.

Example: Oxidation of Ethanol to Ethanoic Acid

Step 1: Ethanol is oxidized to ethanal (aldehyde).

CH₃CH₂OH + [O] → CH₃CHO + H₂O

Step 2: Ethanal is further oxidized to ethanoic acid (carboxylic acid).

CH₃CHO + [O] → CH₃COOH

Overall reaction:

CH₃CH₂OH + 2[O] → CH₃COOH + H₂O

Key point: Carboxylic acids can be formed by the oxidation of alcohols.

The Carboxyl Group

The carboxyl group shows the chemistry of both the carbonyl (C=O) and the hydroxyl (-OH) groups.

In most reactions, the carboxyl group is retained.

However, the reactivity of these molecules is due to the presence of the carbonyl group.

Key point: The carboxyl group shows the chemistry of both the carbonyl and hydroxyl groups. Its reactivity is due to the carbonyl group.

Acidity of Carboxylic Acids

Carboxylic acids are weaker acids than mineral acids.

They produce H⁺ ion when dissolved in water:

RCOOH ⇌ RCOO^- + H⁺

Example:

CH₃COOH ⇌ CH₃COO^- + H⁺

Key point: Carboxylic acids are weaker acids than mineral acids and produce H⁺ ions in water.

Types of Reactions of Carboxylic Acids

The source states that carboxylic acids undergo the following types of reactions:

i) The reaction in which the hydrogen atom of the carboxyl group (-C-O-H) is involved (salt formation).

ii) The reaction in which the -OH group is replaced by another group (-OH).

iii) The reactions involving the carboxyl group as a whole (-COOH).

Key point: Carboxylic acids undergo three main types of reactions: salt formation, replacement of the -OH group, and reactions involving the carboxyl group as a whole.

Summary Table

Intermediate Level

Carboxylic acids:

• Contain the carboxyl group (-COOH).
• The carboxyl group is made up of a carbonyl group (C=O) and a hydroxyl group (-OH).
• The carboxyl group shows the chemistry of both groups.
• In most reactions, the carboxyl group is retained.
• The reactivity is due to the carbonyl group.
• Carboxylic acids are weaker acids than mineral acids.
• They produce H⁺ ions when dissolved in water.

Formation:

• By the oxidation of alcohols.
• Example: Ethanol → Ethanal → Ethanoic acid.

Types of reactions:

• Salt formation (involving the H atom of the -COOH group).
• Replacement of the -OH group.
• Reactions involving the -COOH group as a whole.

Key point: Carboxylic acids contain the -COOH group, are formed by the oxidation of alcohols, and undergo three main types of reactions.

Solved Example

Example: Write the Equation for the Oxidation of Ethanol to Ethanoic Acid

Question: Write the equations for the oxidation of ethanol to ethanoic acid.

Solution:

Step 1: Ethanol is oxidized to ethanal.

CH₃CH₂OH + [O] → CH₃CHO + H₂O

Step 2: Ethanal is further oxidized to ethanoic acid.

CH₃CHO + [O] → CH₃COOH

Overall reaction:

CH₃CH₂OH + 2[O] → CH₃COOH + H₂O

Final Answer: The overall equation is CH₃CH₂OH + 2[O] → CH₃COOH + H₂O.

Important Points

• - Carboxylic acids = organic compounds with the carboxyl group (-COOH).
• - General formula: RCOOH.
• - The carboxyl group is made up of a carbonyl group (C=O) and a hydroxyl group (-OH).
• - The carboxyl group shows the chemistry of both the carbonyl and hydroxyl groups.
• - In most reactions, the carboxyl group is retained.
• - The reactivity of carboxylic acids is due to the carbonyl group.
• - Carboxylic acids are weaker acids than mineral acids.
• - They produce H⁺ ions when dissolved in water.
• - Formation: By the oxidation of alcohols.
• - Types of reactions:
• 1. Salt formation (involving the H atom of the -COOH group).
• 2. Replacement of the -OH group.
• 3. Reactions involving the -COOH group as a whole.
• - Examples:
• - Methanoic acid (HCOOH) — formic acid
• - Ethanoic acid (CH₃COOH) — acetic acid
• - Propanoic acid (CH₃CH₂COOH)
• - Butanoic acid (CH₃CH₂CH₂COOH)

Remember

• - Carboxylic acids = organic compounds with a -COOH group.
• - General formula: RCOOH.
• - Carboxyl group = carbonyl group (C=O) + hydroxyl group (-OH).
• - Weaker acids than mineral acids.
• - Produce H⁺ ions in water.
• - Formed by oxidation of alcohols.
• - Types of reactions: salt formation, replacement of -OH, reactions involving -COOH as a whole.
• - Examples: Methanoic acid, Ethanoic acid, Propanoic acid, Butanoic acid.

Common Mistakes

Quick Revision

Carboxylic Acids:

Carboxylic acids are characterized by the presence of the carboxyl group (-COOH) attached to a hydrocarbon chain. The carboxyl group shows the chemistry of both the carbonyl (C=O) and the hydroxyl (-OH) groups. In most reactions, the carboxyl group is retained. However, the reactivity of these molecules is due to the presence of the carbonyl group.

Carboxylic acids are weaker acids than mineral acids. They produce H⁺ ion when dissolved in water.

• RCOOH ⇌ RCOO^- + H⁺

Types of reactions of carboxylic acids:

i) The reaction in which the hydrogen atom of the carboxyl group (-C-O-H) is involved (salt formation).

ii) The reaction in which the -OH group is replaced by another group (-OH).

iii) The reactions involving the carboxyl group as a whole (-COOH).

Formation of carboxylic acids:

Carboxylic acids can be formed by the oxidation of alcohols.

Example: Ethanol is readily oxidized to aldehyde, which further oxidizes to carboxylic acids in the presence of oxidizing agents such as potassium dichromate or potassium permanganate(VII) in an acidic medium.

• CH₃CH₂OH + [O] → CH₃CHO + H₂O

• CH₃CHO + [O] → CH₃COOH

60-Second Revision

• Carboxylic acids = organic compounds with a -COOH group.
• General formula: RCOOH.
• Carboxyl group = carbonyl group (C=O) + hydroxyl group (-OH).
• Weaker acids than mineral acids.
• Produce H⁺ ions in water.
• Formed by oxidation of alcohols.
• Types of reactions: salt formation, replacement of -OH, reactions involving -COOH as a whole.
• Examples: Methanoic acid, Ethanoic acid, Propanoic acid, Butanoic acid.
• Reactivity due to the carbonyl group.
• ⚠️ Warning: carboxylic acids are weaker acids than mineral acids — they do not completely ionize in water.