Question

Why do alkyl iodides become brown or violet on standing?

Why do alkyl iodides develop brown or violet colour on long standing?

Answer 1

• Alkyl iodides develop brown or violet colour on standing or on long standing because they gradually decompose to release free iodine (I₂).
• The C–I bond in alkyl iodides is relatively weak and can undergo homolytic or heterolytic cleavage over time, especially on exposure to light or air, liberating iodine atoms.
• These iodine atoms then combine to form molecular iodine, which imparts a characteristic brown or violet colour to the sample.