Alkanals and Alkanones - Preparations, Properties and Uses | Chemistry for JAMB PDF Download

Alkanals and Alkanones: General Properties and Uses

• Alkanals (also known as aldehydes) and alkanones (also known as ketones) are organic compounds that contain a carbonyl group (C=O) as their functional group.
• General properties of Alkanals:
  • Alkanals have a terminal carbonyl group, which means the carbonyl carbon is bonded to at least one hydrogen atom.
  • They are named by replacing the -e ending of the corresponding alkane with -al.
  • Examples of alkanals include formaldehyde (HCHO) and acetaldehyde (CH₃CHO).
• General properties of Alkanones:
  • Alkanones have an internal carbonyl group, which means the carbonyl carbon is bonded to two other carbon atoms.
  • They are named by replacing the -e ending of the corresponding alkane with -one.
  • Examples of alkanones include acetone (CH₃COCH₃) and propanone (CH₃COCH₂CH₃).
  • Both alkanals and alkanones have polar carbonyl groups, which give them unique chemical and physical properties.
• Uses of Alkanals and Alkanones:
  • Alkanals are commonly used as reducing agents, disinfectants, and in the production of various chemicals and pharmaceuticals.
  • Alkanones are widely used as solvents, flavoring agents, and in the synthesis of pharmaceuticals, plastics, and other industrial products.

Chemical Test to Distinguish between Alkanals and Alkanones

• One of the commonly used chemical tests to distinguish between alkanals and alkanones is the Tollens' test or silver mirror test.
• Tollens' test:
  • Tollens' reagent is prepared by adding a small amount of silver nitrate (AgNO₃) to aqueous ammonia (NH₃) until the precipitate initially formed dissolves.
  • In a test tube, the unknown compound is mixed with Tollens' reagent and heated in a water bath.
  • Alkanals (aldehydes) will undergo oxidation in the presence of Tollens' reagent, forming a silver mirror on the inner wall of the test tube.
  • Alkanones (ketones), however, do not undergo oxidation and do not produce a silver mirror.
  • This test is based on the fact that alkanals can be oxidized to carboxylic acids, while alkanones cannot be further oxidized under these conditions.