Which of the following reactions will not give pure propane ?

Options

A. `CH_3CH_2Cl+2Na+ClCH_3overset("ether")rarr`
B. `CH_3CH_2CH_2COONaoverset("sodalime")rarr`
C. `CH_3CH=CH_2overset(H_2//Pd)rarr`
D. `CH_3C-=CHoverset(H_2//Pd)rarr`

Answer

To determine which of the following reactions will not yield pure propane, we will analyze each reaction step by step.

### Step 1: Analyze the First Reaction
The first reaction involves ethyl chloride (C2H5Cl) and methyl chloride (CH3Cl) reacting in the presence of sodium (Na). This is a Wurtz reaction.

**Wurtz Reaction:**
- In a Wurtz reaction, two alkyl halides react with sodium to form a higher alkane.
- Here, the products will include butane (C4H10) and possibly other hydrocarbons due to the presence of both ethyl and methyl halides.

**Conclusion for Step 1:**
- Since multiple products are formed (butane and possibly others), the propane produced will not be pure.

### Step 2: Analyze the Second Reaction
The second reaction involves hydrogenation of an alkyne (specifically, 1-butyne) in the presence of a catalyst like platinum (Pt) or palladium (Pd).

**Hydrogenation Reaction:**
- The triple bond in the alkyne is converted to a double bond and then to a single bond, yielding propane (C3H8).
- The catalyst is removed after the reaction, resulting in pure propane.

**Conclusion for Step 2:**
- This reaction will yield pure propane.

### Step 3: Analyze the Third Reaction
The third reaction involves the sodium salt of a carboxylic acid being treated with soda lime (NaOH + CaO).

**Decarboxylation Reaction:**
- This reaction removes CO2 and produces a hydrocarbon.
- The end product is propane (C3H8), which is pure because the reaction conditions are controlled.

**Conclusion for Step 3:**
- This reaction will also yield pure propane.

### Step 4: Analyze the Fourth Reaction
The fourth reaction is similar to the second, involving hydrogenation of an alkyne.

**Hydrogenation Reaction:**
- Similar to the second reaction, this will convert the alkyne to propane.
- The catalyst is removed, resulting in pure propane.

**Conclusion for Step 4:**
- This reaction will yield pure propane as well.

### Final Conclusion
After analyzing all four reactions, we find that the **first reaction** (Wurtz reaction involving ethyl chloride and methyl chloride) will not yield pure propane due to the formation of multiple products that are difficult to separate.

### Answer:
**The reaction that will not give pure propane is the first reaction.**

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