Animated Solution for Chemistry - Organic Chemistry: The major products obtained from the reactions in List-II are the reactants for the named reactions mentioned in List-I. Match List-I with List-II and choose the correct option.
List-I
(P)
Etard reaction
(Q)
Gattermann reaction
(R)
Gattermann-Koch reaction
(S)
Rosenmund reduction
List-II
(1)
Acetophenone Zn-Hg, HCl
(2)
Toluene (i) KMnO4, KOH, Δ (ii) SOCl2
(3)
Benzene CH3Cl, anhyd. AlCl3
(4)
Aniline NaNO2/HCl, 273-278 K
(5)
Phenol Zn, Δ
Select Matching Pairs:
* Multiple Allowed
PMatches
QMatches
RMatches
SMatches
Visualized Solution
Problem Orientation
Goal: Evaluate products of List-II and match them as reactants for List-I.
Reaction 1: Clemmensen Reduction
1. Acetophenone Zn-Hg, HCl Ethylbenzene
Clemmensen Reduction converts carbonyl group to methylene group.
Imagine you are a detective, and every chemical reaction is a clue. In this JEE Advanced problem, we are given a set of starting materials and reagents in List II.
Our mission is to deduce the major products of these reactions. But the mystery doesn't end there!
These products are actually the starting materials for a set of famous named reactions in List I. We need to connect the dots and find the perfect match.
Decoding List II
The Reactions
Let's break down the reactions in List II one by one.
Reaction 1: The Clemmensen Reduction
We start with acetophenone reacting with zinc amalgam (Zn-Hg) and concentrated HCl.
This is the classic Clemmensen reduction. It completely strips the oxygen from the carbonyl group, converting the acetyl group into an ethyl group.
Ph-COCH3Zn-Hg, HClPh-CH2CH3
The product is ethylbenzene.
Reaction 2: Oxidation and Chlorination
Next, toluene is treated with alkaline KMnO4 under heat.
This is a brutal oxidation. The strong oxidizing agent chews up the methyl side chain, converting it entirely into a carboxylic acid group, yielding benzoic acid.
Then, we hit it with thionyl chloride (SOCl2). This replaces the hydroxyl group of the acid with a chlorine atom.
Ph-CH3KMnO4,ΔPh-COOHSOCl2Ph-COCl
The final product here is benzoyl chloride.
Reaction 3: Friedel-Crafts Alkylation
Here, benzene reacts with methyl chloride in the presence of anhydrous AlCl3.
The Lewis acid generates a methyl carbocation, an eager electrophile that attacks the electron-rich benzene ring.
Ph-H+CH3ClAlCl3Ph-CH3
This electrophilic aromatic substitution gives us toluene.
Reaction 4: Diazotization
Aniline is treated with sodium nitrite (NaNO2) and HCl at a chilly 273−278 K.
These conditions generate nitrous acid in situ, which reacts with the primary amine to form a highly versatile diazonium salt.
Ph-NH2NaNO2,HClPh-N2+Cl−
The product is benzene diazonium chloride.
Reaction 5: Reduction of Phenol
Finally, phenol is heated with zinc dust.
Zinc acts as a reducing agent, grabbing the oxygen atom to form stable zinc oxide, leaving the aromatic ring intact.
Ph-OHZn, ΔPh-H
The product is simply benzene.
Connecting the Dots
Matching with List I
Now that we have our arsenal of products, let's see which named reaction they belong to.
The Etard Reaction (P)
The Etard reaction uses chromyl chloride (CrO2Cl2) to partially oxidize toluene into benzaldehyde.
The required reactant is toluene. Looking at our list, toluene was produced in Reaction 3.
Therefore, P matches with 3.
The Gattermann Reaction (Q)
This reaction synthesizes halobenzenes using a diazonium salt and copper powder with a halogen acid.
The required reactant is benzene diazonium chloride. We synthesized this exactly in Reaction 4.
Therefore, Q matches with 4.
The Gattermann-Koch Reaction (R)
This is a formylation reaction where benzene is treated with carbon monoxide and HCl to yield benzaldehyde.
The required reactant is benzene. We obtained pure benzene in Reaction 5.
Therefore, R matches with 5.
The Rosenmund Reduction (S)
This reaction selectively reduces an acyl chloride to an aldehyde using hydrogen gas and a poisoned palladium catalyst (Pd/BaSO4).
The required reactant is an acyl chloride, specifically benzoyl chloride in this context. We produced this in Reaction 2.
Therefore, S matches with 2.
The Final Verdict
By systematically evaluating each chemical transformation and recalling the specific requirements of classic named reactions, we have successfully unraveled the matrix.
The final correct matching is P → 3, Q → 4, R → 5, S → 2.
This problem is a beautiful testament to the interconnected nature of organic synthesis!
