Some Commercially Important Carboxylic Acids

(i) Methanoic acid [Formic acid HCOOH]

It occurs in a variety of biting and stingins plants and insects. It is manufactured by the reaction of carbomonoxide with sodium hydroxide under pressure at 473 K. Sodium methanoate is obtained which is acidified and distilled to give the acid.

Methanoic acid is a colorless, pungent smelling liquid with a boiling point 373.5 K. Due to the presence of aldehyde - like hydrogen, it is a powerful reducing agent. It reduces Tollen's reagent and Fehling's solution.

It is used in rubber, textile, dyeing, leather and electroplating industries.

(ii) Ethanoic acid (Acetic acid CH

₃COOH)

It is the main constituent of vinegar and is obtained by fermentation of molasses in the presence of air.

Industrially, it is obtained by oxidation of ethanol with air in the presence of cobalt acetate catalyst.

Also the carbonylation of methanol in the presence of rhodium catalyst gives acetic acid.

Ethanoic acid a colorless liquid with a pungent odor boils at 391 K. It freezes at an unusually high temperature (Melting point 298 K) forming ice like crystals. The water free ethanoic acid obtained by melting of the crystals is called glacial acetic acid. It is used in the manufacture of rayon and in plastic, rubber and silk industries. It is also used as a solvent. Vinegar is used in the food industry.

Benzoic acid is prepared by oxidation of toluene. In the form of esters, benzoic acid is used in perfume industry. The salts of benzoic acid like sodium benzoate are used as food preservatives.

1,2-Benzene dicarboxylic acid (Phthalic acid) is used in the manufacture of plasticizers and resins.

1,4-Benzene dicarboxylic acid (terephthalic acid) is a basic raw material for polyester.