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 (NaOH), we can follow these steps:

### Step 1: Identify the Reactants
Acetaldehyde (CH3CHO) is the reactant in this case. It contains an aldehyde functional group and has alpha hydrogen atoms, which are crucial for the reaction.

**Hint:** Look for the functional groups and alpha hydrogens in the reactant.

### Step 2: Understand the Role of Caustic Soda
Dilute NaOH acts as a base in this reaction. It facilitates the formation of an enolate ion from acetaldehyde due to the presence of alpha hydrogen.

**Hint:** Remember that bases can deprotonate alpha hydrogens to form enolate ions.

### Step 3: Formation of Enolate Ion
When acetaldehyde is treated with dilute NaOH, the alpha hydrogen is removed, forming an enolate ion. The reaction can be represented as follows:

\[ \text{CH}_3\text{CHO} + \text{NaOH} \rightarrow \text{CH}_2\text{CHO}^- + \text{H}_2\text{O} \]

**Hint:** The enolate ion is a key intermediate in aldol reactions.

### Step 4: Aldol Condensation
The enolate ion can then attack another molecule of acetaldehyde. This results in the formation of a β-hydroxy aldehyde, known as an aldol. The reaction can be summarized as:

\[ \text{CH}_2\text{CHO}^- + \text{CH}_3\text{CHO} \rightarrow \text{CH}_3\text{CH(OH)CH}_2\text{CHO} \]

This compound is known as 3-hydroxybutanal, or simply an aldol.

**Hint:** Aldol reactions typically yield β-hydroxy carbonyl compounds.

### Step 5: Final Product
The final product of this reaction is an aldol, specifically 3-hydroxybutanal. This compound can further undergo dehydration to form an α,β-unsaturated aldehyde, but in this case, we are primarily interested in the aldol product.

**Hint:** Identify the final product based on the aldol condensation mechanism.

### Conclusion
The compound obtained when acetaldehyde is treated with a dilute solution of caustic soda is **aldol** (3-hydroxybutanal).

**Final Answer:** C) Aldol