Question

An organic compound (A) with molecular formula, $C_8{H}_{8}O$ forms an orange-red precipitate with 2,4-DNP reagent and gives yellow precipitate on heating with iodine in the presence of sodium hydroxide.It neither reduces Tollens' or Fehling's reagent, nor does it decolourise bromine water or Baeyer's reagent.On drastic oxidation with chromic acid, it gives a carboxylic acid (B) having molecular formula, $C_7{H}_6{O}_2$. Identify the compounds (A) and (B) and explain the reactions involves.

Answer 1

Given,

1. "A" forms an Orange colour precipitate with $2,4$ Dinitrophenylhydrazine. It means that A is an aldehyde or Ketone.

2. It is given that A gives iodoform test, so it must have $C{H}_3-CO$ group.

3. Also given " A" does not reduce Tollen or Fehling's reagent.

$\Rightarrow$ A must be a ketone.

4. Given A has molecular formula $C_8{H}_{8}O$

$\Rightarrow$ A is unsaturated, but also given A doesn't decolorize bromine water ort Bayer's reagent

$\Rightarrow$ A is unsaturated, having benzene ring.

5. It is given that "A" on drastic oxidation changes to carboxylic acid "B".

As A is a ketone B will have one less carbon than A

$\Rightarrow$ A can be $C_6{H}_5-COC{H}_3$

6. Also, a Total number of carbon atoms given in A are $8,\left[C_8{H}_{8}O\right]$

$\Rightarrow$ A is acetophenone $[C_6{H}_5-CO-C{H}_3]$

7. Molecular formula of B is $C_7{H}_6{O}_2$

$\Rightarrow$ B is Benzoic acid.

$\therefore$ A is Acetophenone, B is Benzoic Acid.