The Cannizzaro reaction is a type of redox reaction where one molecule is reduced to an alcohol, and the other is oxidized to a carboxylate anion. This reaction occurs in aldehydes without an alpha-hydrogen under basic conditions.
The question asks for the major product of the reaction given. The key to solving this problem is recognizing that the reaction involves an aldol condensation. In this scenario, propanal (CH3CH2CH=O) reacts with excess formaldehyde (HCHO) in the presence of an alkali.
Steps to solve the problem:
Identify the Reactants and Reagents: The reactants are propanal and formaldehyde, and the reagent is an alkali, which is typical for an aldol condensation reaction.
Aldol Condensation Reaction: This involves the formation of a β-hydroxy aldehyde or ketone. Here, the alpha-hydrogen of propanal will be deprotonated by the alkali, generating an enolate ion.
Formation of the Aldol Product: The enolate ion will attack the carbonyl carbon of formaldehyde. This forms a β-hydroxy aldehyde as an intermediate.
Dehydration to Form the Final Product: The β-hydroxy aldehyde undergoes dehydration (loss of water) to form an α,β-unsaturated carbonyl compound.
Conclusion: The major product of this reaction is the α,β-unsaturated aldehyde.
Hence, the major product of the reaction is illustrated in the image above, matching the second option from the provided choices.
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Approach Solution -2
The reaction between propanal and formaldehyde in alkaline medium proceeds via the crossed Cannizzaro mechanism:
Reaction Mechanism: 1. Nucleophilic attack by hydroxide on formaldehyde (more reactive carbonyl) 2. Hydride transfer to propanal 3. Formaldehyde gets oxidized to formate ion 4. Propanal gets reduced to propanol
Key Points: - Formaldehyde always oxidizes to formate in Cannizzaro reactions - The other aldehyde (propanal) reduces to alcohol - No alpha-hydrogen required for this disproportionation
The major organic product is propanol (CH3CH2CH2OH).
