When `CH_(3)CHO` is reacted in the presence of a base with excess of HCHO, which statement is true ?

Options

A. Only aldol-type (Claisen-schmidt) reaction takes place.
B. Only Cannizzaro-type (crossed Cannizzaro) takes place.
C. First aldol-type and then Cannizzaro-type reaction takes place.
D. Fiest Cannizzaro-type and then aldol-type reaction takes place.

Answer

To solve the problem, we need to analyze the reaction between acetaldehyde (CH₃CHO) and formaldehyde (HCHO) in the presence of a base. The reaction involves two main steps: aldol condensation and Cannizzaro reaction.

### Step-by-Step Solution:

1. **Identify the Reactants**:
The reactants in this reaction are acetaldehyde (CH₃CHO) and formaldehyde (HCHO).

2. **Understand the Reaction Conditions**:
The reaction occurs in the presence of a base, which is necessary for both aldol condensation and Cannizzaro reaction.

3. **Aldol Condensation**:
- When acetaldehyde (CH₃CHO) reacts with formaldehyde (HCHO) in the presence of a base, it undergoes aldol condensation.
- The base deprotonates the acetaldehyde, allowing it to act as a nucleophile. It attacks the carbonyl carbon of formaldehyde.
- This leads to the formation of a β-hydroxy aldehyde (an aldol), specifically 3-hydroxybutanal (CH₃CH(OH)CH₂CHO).

4. **Formation of a β-Hydroxy Compound**:
- The product from the aldol condensation is a β-hydroxy compound, which can be represented as CH₃CH(OH)CH₂CHO.

5. **Further Reaction - Cannizzaro Reaction**:
- In the presence of excess formaldehyde and a strong base, the β-hydroxy compound can undergo a Cannizzaro reaction.
- In this reaction, one molecule of formaldehyde is oxidized to formic acid (HCOOH), while another molecule is reduced to methanol (CH₃OH).
- The aldehyde group of the β-hydroxy compound can also undergo further reactions leading to the formation of carboxylic acids and alcohols.

6. **Final Products**:
- The final products of the reaction include methanol (CH₃OH), formic acid (HCOOH), and possibly other alcohols and carboxylic acids depending on the reaction conditions.

7. **Conclusion**:
- Therefore, the correct statement regarding the reaction of acetaldehyde with excess formaldehyde in the presence of a base is that it undergoes aldol condensation followed by a Cannizzaro reaction.

### Final Answer:
The correct statement is that acetaldehyde (CH₃CHO) reacts with excess formaldehyde (HCHO) in the presence of a base to undergo aldol condensation followed by a Cannizzaro reaction, leading to the formation of alcohols and carboxylic acids.