Question

Which of the following will give yellow precipitate with Iodine and alkali?
(A) Propan-2-ol
(B) Benzophenone
(C) Methyl acetate
(D) Acetamide

Answer 1

Hint In order to find which of the organic compounds reacts with Iodine and alkaline to give yellow precipitate, we must first know what type of the reaction is taking place. The reaction taking place is an Iodoform test or Haloform reaction.

Complete step by step solution:
The yellow precipitate which is produced is due to the formation of the Iodoform. Iodoform is an organic chemical compound which has a chemical formula of $CH{I_3}$. It belongs to the family of halogen. Iodoform can also be referred to as Triiodomethane. Iodoform will exist as a pale-yellow crystalline substance. It has a very different and penetrating odour. Iodoform has a volatile substance. Iodoform is mostly used as an antiseptic and disinfectant. This is because of its non-irritant action.
The iodine and alkali like NaOH will react with each other to form NaOI.
The organic compound like Acetophenone and Propan-2-ol will react with NaOI to form Iodoform, $CH{I_3}$which gives the yellow precipitate. The Haloform reaction of Iodoform reaction is given below:
${C_6}{H_5}COC{H_3} + NaOH + {I_2} \to {C_6}{H_5}COONa + CH{I_3}$
$C{H_3}CH(OH)C{H_3} + NaOH + {I_2} \to C{H_3}COONa + CH{I_3}$
The other compounds which will undergo Iodoform test other than Acetophenone and 2- Hydroxy propane are
- ethanol
- acetaldehyde
- Methyl alcohol
- secondary alcohol which contains methyl group
The Acetamide and Methyl acetate will not give yellow precipitate on reaction with Iodine and alkali.

Therefore, the correct answer is option (A) and (B)

Note: Iodoform is having a good antiseptic property. Antiseptics are those chemicals which are used on the living tissues such as the wounds, cuts and skin diseases. It will come in contact with the organic matter of our skin and will liberate free Iodine which will act as the antiseptic.