Organic Chemistry

Module 3. Carboxylic acids

Lesson 10B
SUBSTITUTED CARBOXYLIC ACIDS: HALOGEN, KETO AND HYDROXY ACIDS AND THEIR IMPORTANT REACTIONS

10.B.1 Reactions of Carboxylic Acids

1. Reactions with alkali (Neutralization)

• Carboxylic acids are recognized by their acidity
• Like conventional acids (HCl, H₂S0₄, 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

• 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

2R-COOH + Na₂CO₃ = 2R-COONa + H₂O + CO₂
R-COOH + NaHCO₃ = R-COONa + H₂O + CO₂

• When the salt is treated with mineral acid- it is 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

3. Conversion into aldehyde and ketone

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

(HCOO)₂Ca + (R-COO)₂Ca = 2RCHO + 2CaCO₃

aldehyde

• When Ca salt of an acid other than formic acid is heated – ketone will form

4. Substitution of side chain

• Chlorine reacts with carboxylic acids to form choloro substituted carboxylic acids