Question

Explain the following briefly:

Alkyl iodides usually become brown on standing.

Answer 1

1. Alkyl iodides are unstable compounds in the presence of air and sunlight.
2. On standing, they undergo slow oxidation and photochemical decomposition.
3. During this process, some free iodine (I₂) is liberated.
4. Free iodine has a distinct brown colour.

Therefore, alkyl iodides usually turn brown on standing because of the release of iodine.