Question

Formaldehyde undergoes Cannizzaro reaction because
(A) It has alpha-hydrogen atom.
(B) It does not have alpha-hydrogen atom.
(C) It does not undergo self-oxidation and reduction on heating with concentrated alkali.
(D) It undergoes self-oxidation and reduction on heating with concentrated alkali.

• A. It does not have alpha-hydrogen atom
• B. It has alpha-hydrogen atom
• C. It does not undergo self-oxidation and reduction on heating with concentrated alkali
• D. It undergoes self-oxidation and reduction on heating with concentrated alkali

Answer 1

The Correct Option is A

The Cannizzaro reaction is a redox reaction where an aldehyde without an alpha-hydrogen atom undergoes simultaneous oxidation and reduction when treated with a strong base, typically a concentrated alkali. This reaction involves the following steps: 

• The aldehyde molecule that does not have an alpha-hydrogen atom acts as a substrate.
• When exposed to concentrated alkali, one molecule of the aldehyde is reduced to form an alcohol, while another molecule is oxidized to form a carboxylate ion.
• This process is only viable for aldehydes that lack an alpha-hydrogen atom, as the presence of an alpha-hydrogen facilitates enol formation, leading to alternative reactions such as aldol condensation.

In this context, formaldehyde (HCHO) undergoes the Cannizzaro reaction because it does not contain an alpha-hydrogen atom, making it suitable for this reaction pathway.

Therefore, the correct answer is (A) It does not have alpha-hydrogen atom.

Answer 2

The Cannizzaro reaction is a disproportionation reaction of aldehydes that lack α-hydrogen atoms. In this reaction, two molecules of an aldehyde react in the presence of a strong base to produce a primary alcohol and a carboxylic acid.

Let's analyze each statement:

(A) It does not have alpha-hydrogen atom.: This is correct. Formaldehyde lacks α-hydrogen atoms, which is a requirement for the Cannizzaro reaction.

(B) It has alpha-hydrogen atom.: Formaldehyde (HCHO) does not have any α-hydrogen atoms. The α-carbon is the carbonyl carbon itself, which is directly bonded to hydrogen atoms.

(C) It does not undergo self-oxidation and reduction on heating with concentrated alkali.: This is incorrect. The Cannizzaro reaction involves self-oxidation and reduction.

(D) It undergoes self-oxidation and reduction on heating with concentrated alkali.: This is correct. The Cannizzaro reaction is a disproportionation reaction, which involves self-oxidation and reduction.

Since the Cannizzaro reaction occurs specifically for aldehydes without α-hydrogen atoms, and it involves self-oxidation and reduction, the correct reasons are (A) and (D).

However, the most direct reason why Formaldehyde undergoes the Cannizzaro reaction is because it lacks an alpha hydrogen.

Therefore, the most appropriate answer is:

Option 1: (A) It does not have an alpha-hydrogen atom