Carboxylic acids

Carboxylic acids are the compounds containing the carboxyl functional group    in their molecule. Their general formula is C_nH_2n+1COOH. The simplest carboxylic acid is methanoic acid (formic acid) having molecular formula HCOOH.

Fatty Acids

Fatty acids are the monocarboxylic acids which contain a long chain of carbon atoms. The minimum number of carbon atoms in fatty acids is 15. These are called as fatty acids because these are present mostly in fats and oils. For example, palmitic acid (C₁₅H₃₁COOH), oleic acid (C₁₇H₃₃COOH) and stearic acid (C₁₇H₃₅COOH).

Uses of Fatty Acids

Fatty acids are used in eatables, cold drinks, soaps and in medicines.

Nomenclature of carboxylic Acids

According to IUPAC system, the name of carboxylic acid is derived by replacing the terminal ‘e’ of the name of the corresponding alkane with ‘oic acid’.

Common Name	IUPAC Name	Molecular Formula
Formic acid	Methanoic acid
Acetic acid	Ethanoic acid
Propanic acid	Propanoic acid
Butric acid	Butanoic acid

Ethanoic Acid or Acetic Acid

Ethanoic acid can be prepared by following methods :

1. From Ethanol

Ethanoic acid can also be prepared by oxidation of ethanol in the presence of oxidizing agent K₂Cr₂O₇ and H₂SO₄.

2. From Methyl Cyanide

When water is added into methyl cyanide then upon hydrolysis ethanoic acid is produced.

Properties of Ethanoic Acid

Physical Properties

Following are the physical properties of ethanoic acid:

1. It is a colourless liquid with pungent odour.
2. It freezes below 16.5⁰C.
3. Its boiling point is 118⁰C.
4. It is soluble in water.

Chemical Properties

Following are the important chemical reactions of acetic acid :

1. Reaction with Alcohols or Esterification

When acetic acid reacts with ethanol in the presence of conc. H₂SO₄ as catalyst sweet smelling esters are formed. This process is called esterification.

2. Reaction with Sodium Metal

Acetic acid reacts with sodium metal to produce sodium acetate and hydrogen gas.

3. Decarboxylation Reaction or Reaction with Soda Lime

Loss of carbon dioxide from molecule of sodium or potassium salt of carboxylic acid is called decarboxylation. In this reaction, when sodium or potassium salts of carboxylic acids are heated after mixing with soda lime (NaOH + CaO) then methane gas is produced.

Preparation of Soda Lime

Sodalime can be prepared for decarboxylation reaction by mixing 3 parts by volume of NaOH with 1 part by volume of CaO.

4. Reaction with Ammonia

Acetic acid reacts with ammonia to form acid amides.

Uses of Acetic Acid

Following are the uses of acetic acid:

1. It is used as a solvent and chemical reagent in laboratories.
2. It is used as a preservative.
3. It is used in preparation of acetone and acetic anhydride.
4. It is used in coagulation of latex of rubber.
5. It is used as vinegar in cooking.
6. It is used in manufacture of rayon and plastics.

Test your understanding and answer these questions:

1. What are caboxylic acids? give examples.