Nature's Chemistry: Carboxylic Acids

Nature’s Chemistry: Carboxylic Acids

Overview of Carboxylic Acids

  • Carboxylic acids are a class of organic compounds that contain a carboxyl functional group, -COOH.
  • They have the general formula CnH2nO2, where n is the number of carbon atoms.
  • The simplest carboxylic acid is formic acid, HCOOH, and the second simplest is acetic acid, CH3COOH, which gives vinegar its sour taste.

Classification of Carboxylic Acids

  • Carboxylic acids can be classified as aliphatic or aromatic depending on the nature of the R group.
  • Aliphatic carboxylic acids have an alkyl group (which can be a straight chain or branched), while aromatic carboxylic acids have an aryl group (a group derived from aromatic rings like benzene).

Properties of Carboxylic Acids

  • Carboxylic acids are polar compounds and can form hydrogen bonds with each other, leading to higher boiling and melting points compared to similar-sized alcohols.
  • They are weak acids and so partially dissociate in water to produce H+ ions, hence their acidic properties.
  • Lower members (up to four carbon atoms) are soluble in water due to the formation of hydrogen bonds. As chain length increases, solubility decreases.

Reactions of Carboxylic Acids

  • Carboxylic acids can react with alkalis to form a salt and water, a typical reaction of an acid.
  • They can undergo a reaction of esterification with alcohols in the presence of a catalyst, resulting in an ester and water.
  • Carboxylic acids can be reduced to aldehydes and then to primary alcohols by a strong reducing agent such as lithium aluminium hydride.

Uses of Carboxylic Acids

  • Carboxylic acids are often used in the food industry with acetic acid used as vinegar and citric acid providing the sour taste in citrus fruits.
  • They are also found in soaps and detergents, where the sodium or potassium salts of fatty acids are used.
  • Carboxylic acids also have applications in the textile industry for the manufacture of synthetic fibres and dyes.
  • Medicinally, carboxylic acid derivatives like aspirin and penicillin have significant uses.