Direct iodination of alkanes using and UV light is practically ineffective under standard laboratory — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

In free-radical halogenation, the thermodynamic feasibility depends on the propagation steps. For iodination, the abstraction of a hydrogen atom by the iodine radical is strongly endothermic ($\approx +33$ kcal/mol), making the overall reaction highly reversible and slow. Consequently, the backward reaction (reduction of alkyl iodide by $HI$) dominates. To force the reaction forward, $HI$ must be removed from the system. This is achieved by adding a strong oxidizing agent like $HIO_3$ or $HNO_3$, which oxidizes $HI$ back to $I_2$ ($5HI + HIO_3 \rightarrow 3I_2 + 3H_2O$).