Organic Chemistry

Module 3. Carboxylic acids

Lesson 8
IMPORTANT REACTIONS OF CARBOXYLIC ACID

8.1 Introduction

8.2 Reactions of carboxylic acids

1. Reactions with alkali (Neutralization)

• Carboxylic acids are recognized by their acidity
• Like conventional acids (HCl, H₂SO₄, HNO₃ etc), carboxylic acids (R-COOH) also react with aqueous hydroxides (e.g. NaOH) to form salt and water - used for determination of the acid

R-COOH + NaOH = R-COONa + H₂O

salt

• Reaction with aqueous sodium bicarbonate and carbonate forms salt, water and evolve carbon dioxide - effervescence - forms the basis for detection of –COOH group in an organic compound

• When the salt is treated with mineral acid= converted back into carboxylic acid

R-COONa + HCl = RCOOH + NaCl

Salt mineral acid carboxylic acid

2. Reduction to alcohol

• Reducing agent - Lithium aluminum hydride - LiAlH₄ -gives excellent yield, but somewhat expensive

Fig. 8.1 Reduction

3. Conversion into aldehyde and ketone

• By heating calcium salt of the acid at high temperature (decarboxylation)
• When a mixture of Ca format and Ca salt of higher acid is heated - aldehyde will form

Fig. 8.2 Decarboxydation

4. Substitution of side chain e.g. Chlorination

Fig. 8.3 HVZ-Reaction

8.3 Dicarboxylic Acids

Fig. 8.4 Dicarboxylic acids

8.4 Tricarboxylic Acid

Fig. 8.5 Tricarboxylic acid

8.4.1 Physical constants of citric acia

• Melting Point: 153°C
• Solubility - 240 g/ 100g water at 25°C
• Ionization constant (K_a x 10^-5): K_a = 74
• Important chelating agent – chelate Ca⁺²

• Improve heat stability of milk
• Processed cheese manufacturing
• Reduces hardness of water
• Improves resistance of human body.