The reaction, `R_(2)CO+4[H] underset("Conc. HCl")overset("Zn-Hg")rarr R_(2)CH_(2)+H_(2)O` is well known as :

Options

A. Wurtz reaction
B. Rsoenmund reduction
C. Kolbe reaction
D. Clemmensen reduction

Answer

To solve the question regarding the reaction \( R_2CO + 4[H] \) in the presence of concentrated HCl and Zn-Hg, we need to identify the name of the reaction. Here’s a step-by-step breakdown:

### Step 1: Identify the Reactants and Products
The reaction involves a carbonyl compound \( R_2CO \) (which can be a ketone) and hydrogen in the presence of concentrated hydrochloric acid (HCl) and a zinc-mercury amalgam (Zn-Hg). The products are \( R_2CH_2 \) (an alkane) and water (H2O).

### Step 2: Understand the Role of Reagents
- **Concentrated HCl**: Acts as a catalyst in this reaction.
- **Zn-Hg (syngamalgam)**: This reagent is known for its reducing properties, particularly in the reduction of carbonyl groups.

### Step 3: Recognize the Type of Reaction
This reaction is a reduction reaction where the carbonyl group (C=O) is reduced to a methylene group (C-H) in the presence of the reducing agent (Zn-Hg) and acid (HCl).

### Step 4: Compare with Known Reactions
Now, we need to compare this reaction with the options provided:
- **Woods Reaction**: Involves the synthesis of higher alkynes from alkyl halides, which does not match.
- **Rosenthal Reduction**: Reduces acyl chlorides to aldehydes, which does not match.
- **Colb Reaction**: Involves sodium phenoxide and carbon dioxide to produce salicylic acid, which does not match.
- **Clemensen Reduction**: Specifically reduces carbonyl compounds (aldehydes and ketones) to alkanes using Zn-Hg in the presence of HCl.

### Step 5: Conclusion
Since the given reaction matches the description of the Clemensen reduction, we conclude that the correct answer is:

**Answer: D. Clemensen Reduction**

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