but 2 enal on reduction with lialh4 and dry ether followed by acidic hydrolysis givesi found that the solution is given asCH3-CH=CH-CH3 +LiAlH4 gives CH3-CH=CH-CH2OH .why dont we do acidic hydrolysis after this

When you reduce 2-enal (which is an α,β-unsaturated aldehyde) using lithium aluminum hydride (LiAlH4) in dry ether, you're initiating a reaction that can lead to the formation of an alcohol. The product you mentioned, CH3-CH=CH-CH2OH, is indeed the result of this reduction. However, the question arises about why we don't perform acidic hydrolysis after this step. Let's break this down step by step.

The Reduction Process

First, let's clarify what happens during the reduction of 2-enal with LiAlH4. This reagent is a strong reducing agent that effectively reduces carbonyl groups. In the case of an α,β-unsaturated aldehyde, the reduction can occur at both the carbonyl carbon and the double bond, but typically, the carbonyl group is reduced first.

Mechanism of Reduction

• The carbonyl carbon of the aldehyde is attacked by a hydride ion (H-) from LiAlH4.
• This results in the formation of an alkoxide intermediate.
• Subsequently, the double bond can also be reduced, leading to the formation of the alcohol.

In your case, the reduction of CH3-CH=CH-CHO (the 2-enal) leads to the formation of CH3-CH=CH-CH2OH. This compound is an allylic alcohol, where the hydroxyl group is attached to a carbon adjacent to a double bond.

Why Not Acidic Hydrolysis?

Now, regarding the acidic hydrolysis step, it's important to understand the role of acid in organic reactions. Acidic hydrolysis typically serves to protonate and stabilize certain intermediates or products. However, in this specific case, performing acidic hydrolysis after the reduction may not be necessary or beneficial for a couple of reasons:

Stability of the Product

The product CH3-CH=CH-CH2OH is already a stable alcohol. Adding acid could potentially lead to unwanted side reactions, such as dehydration, where the alcohol could lose water and form an alkene. This is especially true since the alcohol is adjacent to a double bond, which can lead to elimination reactions under acidic conditions.

Desired Outcome

If the goal is simply to obtain the allylic alcohol, then further treatment with acid could complicate the reaction without providing any additional benefits. The reduction with LiAlH4 is sufficient to yield the desired product, and the subsequent steps may not enhance the outcome.

Conclusion

In summary, after reducing 2-enal with LiAlH4, the product CH3-CH=CH-CH2OH is stable and does not require acidic hydrolysis. Performing such a step could lead to side reactions that might not be desirable. Therefore, in this case, the reduction step is effectively the final step in achieving the desired alcohol product.