Which compound is obtained when acetaldehyde is treated with dilute solution of caustic soda ?

Options

A. Sodium acetate
B. Resinous mass
C. Aldol
D. Ethyl acetate

Answer

To determine the compound obtained when acetaldehyde is treated with a dilute solution of caustic soda (sodium hydroxide), we will follow these steps:

### Step 1: Identify the Reactants
The reactant in this case is acetaldehyde, which has the chemical formula CH₃CHO. When we treat it with a dilute solution of caustic soda (NaOH), we are setting up for a reaction known as aldol condensation.

**Hint:** Remember that acetaldehyde has an aldehyde functional group and alpha hydrogens which are crucial for the reaction.

### Step 2: Understand the Aldol Condensation Reaction
Aldol condensation occurs when a carbonyl compound (like acetaldehyde) with at least one alpha hydrogen reacts with a base. In this case, NaOH acts as a base to abstract an alpha hydrogen from acetaldehyde.

**Hint:** Look for the alpha hydrogens in the structure of acetaldehyde (the hydrogens attached to the carbon adjacent to the carbonyl group).

### Step 3: Formation of the Enolate Ion
When NaOH abstracts an alpha hydrogen from acetaldehyde, it forms an enolate ion. The enolate ion is a resonance-stabilized species that can act as a nucleophile.

**Hint:** The enolate ion is formed by the removal of a proton (H⁺) from the alpha carbon, leading to a negatively charged carbon.

### Step 4: Nucleophilic Attack
The enolate ion then attacks the carbonyl carbon of another acetaldehyde molecule. This forms a beta-hydroxy aldehyde intermediate.

**Hint:** Remember that the carbonyl carbon is electrophilic and can be attacked by the nucleophilic enolate ion.

### Step 5: Formation of the Aldol Product
The intermediate formed is a beta-hydroxy aldehyde, specifically 3-hydroxybutanal (or aldol). The structure can be represented as CH₃-CH(OH)-CH₂-CHO.

**Hint:** The aldol product has both an alcohol (-OH) and an aldehyde (-CHO) functional group.

### Step 6: Final Product
The final product of the aldol condensation is 3-hydroxybutanal, which is often referred to simply as an aldol. This compound can further dehydrate to form an α,β-unsaturated aldehyde, but in the context of this question, we focus on the aldol product.

**Hint:** Make sure to identify the functional groups in the final product to confirm it is indeed an aldol.

### Conclusion
When acetaldehyde is treated with a dilute solution of caustic soda, the compound obtained is an aldol, specifically 3-hydroxybutanal.

**Final Answer:** The compound obtained is **aldol (3-hydroxybutanal)**.