Question

Write the reactions involved in the preparation of iodoform from propan-2-ol.

Answer 1

The reactions involved in the preparation of iodoform (CHI₃) from propan-2-ol (a secondary alcohol) are as follows:

1. Oxidation of propan-2-ol to acetone: Propan-2-ol is oxidized in the presence of iodine and a base (e.g., NaOH) to yield acetone (a methyl ketone).
   \[\mathrm{CH_3CHOHCH_3} \xrightarrow[\text{NaOH}]{I_2} \mathrm{CH_3COCH_3} + \mathrm{2H^+} + 2e^-\]

2. Iodoform reaction: Acetone reacts with iodine in alkaline solution, undergoing successive iodination at the methyl group adjacent to the carbonyl to form a triiodomethyl ketone intermediate, which then cleaves to give iodoform (yellow precipitate) and a carboxylate ion.
   \[\mathrm{CH_3COCH_3} + 3I_2 + 4NaOH \rightarrow \mathrm{CHI_3} \downarrow + \mathrm{CH_3COONa} + 3NaI + 3H_2O\]