CARBOXYLIC ACIDS

 

  • General Molecular formula of Saturated aliphatic monocarboxylic acids is CnH2n+1−COOH

  • Most of the aliphatic mono carboxylic acid obtained by the hydrolysis of natural fats hence they are also known are fatty acids.

  • Acetic acid ((CH3COOH)) is from vinegar (Latin: acetum means Vinegar). The chief constituent of vinegar is Acetic acid.

  • Carboxylic acids with two or more carboxyl groups attached are called dicarborxylic acids, tricarboxylic acids, etc. 

  • Carboxylic acids are derivatives of hydrocarbons in which one or more of the hydrogen atoms in the hydrocarbon have been replaced by a carboxyl group.

             

Carbon atoms

Common name

IUPAC name

Chemical formula

Common location or use

1

Formic acid

Methanoic acid

HCOOH

Insect stings

2

Acetic acid

Ethanoic acid

CH3COOH

Vinegar

3

Propionic acid

Propanoic acid

CH3CH2COOH

Preservative for stored grains

4

Butyric acid

Butanoic acid

CH3(CH2)2COOH

Rancid butter

5

Valeric acid

Pentanoic acid

CH3(CH2)3COOH

Valerian

 

Physical Properties –                                                                                                                                                                                   

  • At ordinary temperature, acetic acid is a colourless liquid with pungent odoured, corrosive liquid.

  • It is miscible with water, alcohol, and ether in all propotions.                                                                

  • It Boils at 391 K. The high Boiling point of acetic acid in comparison to alkanes.  

  • The higher acids are wax like solids and odourless due to their low volatility.

  • Carboxylic acids are also soluble in less polar organic solvents like benzene, ether, alcohol, chloroform etc.

Chemical Properties –

  • Electron with drawing group on C6H5 of aromatic carboxylic acid increases acidity where as, electron donating groups decrease acidity.

  • Electron with drawing groups increase the acidity of carboxylic acids by stabilising the carboxylate ion, the conjugate base through delocalisation of negative charge by inductive effect or resonance effects.

  • Carboxylic acids dissociate in water to give resonance stabilized carboxylate anions. The strength of an acid is given by its pKa value pKa=-logKa where Ka=acid dissociation constant

  • Lesser the pKa<1 value, stronger the acid

  • Increase in the number of Cl atoms at α - position (-I effect) increases the acidic strength and pKa value

 

Uses of Carboxylic Acid-

  • It is a good solvent.

  • In the preparation of acetates, acetones ,acetic anhydride.

  • In the prepararation perfumes, dyes, drugs

  • For curing meat and fish