Carboxylic acids

 Carboxylic acids are those compounds that contain -COOH as a functional group. The functional group         -COOH   comprises the carbonyl group (c-o) and a hydroxyl group(O-H).  All aliphatic carboxylic acids are also called fatty acids as the high members of its series are derived from fats and oils.

Properties of Carboxylic acids:

•  The C1 to C3 are colorless liquids with a pungent smell.
•  The C4 to C6 are colorless liquids with an unpleasant smell. 
• The C1 to C4 are very soluble in water as these form intermolecular hydrogen bonds.
• With the increase of the carbon numbers, the solubility is deceased.
•  Boiling Points:

                          The boiling point of carboxylic acids is increasing regularly with the increase in the number of carbon atoms. These compounds have high boiling points due to strong intermolecular hydrogen bonding. 

Formic Acid(HCOOH)  Acetic Acid(CH3COOH)  Propanoic Acid(CH3CH2COOH)

   100C(373K)                      118C(391K)                       141C  (424K)

• Melting Points: 

             The melting point of carboxylic acids is increasing irregularly. It is observed that the melting point of carboxylic acids containing an even number of carbon atoms is more than the B.P of the next higher and lower odd carbon atom member.

Propanoic acid      Butyrnoic  acid                Pentanoic acid

          (3 carobon )                      (4 carbon)                                                (5 carbon)

         - 22C(251k)            -6C(261K)                       -36C(237k)

• The carboxylic acids form dimmer in non-polar solvents like Benzene. However, in polar solvents, these form hydrogen bond with solvent and no dimerization take place. 

                            

• This dimer is formed due to intermolecular hydrogen bonding. 
• The molecular mass of the dimmer is double that of the single carboxylic aid and it is 8 membered ring.