Question

Which one of the following undergoes reaction with \(50 \%\) sodium hydroxide solution to give the corresponding alcohol and acid? (a) phenol (b) benzaldehyde (c) butanal (d) benzoic acid

Short answer

Benzaldehyde undergoes the Cannizzaro reaction to form benzyl alcohol and benzoic acid.

Step-by-step solution

Understand the Reaction

The reaction in question is a Cannizzaro reaction. This is a redox reaction where two molecules of a non-enolizable aldehyde react with a concentrated base to form an alcohol and a carboxylic acid.

Identify the Suitable Compound

In a Cannizzaro reaction, the aldehyde should not have an alpha hydrogen. If an aldehyde has no alpha hydrogen, it is termed non-enolizable. Among the options, benzaldehyde fits the criteria because it lacks an alpha hydrogen.

Analyze Each Option

- Phenol does not participate in Cannizzaro reaction as it is not an aldehyde. - Benzaldehyde is a suitable candidate for Cannizzaro reaction since it does not have an alpha hydrogen. - Butanal contains alpha hydrogen, making it unsuitable for Cannizzaro reaction. - Benzoic acid is a carboxylic acid and does not undergo Cannizzaro reaction. Thus, benzaldehyde is the substance that reacts.

Predict the Reaction Products

When benzaldehyde undergoes a Cannizzaro reaction with concentrated sodium hydroxide, one molecule of benzaldehyde is reduced to benzyl alcohol while another is oxidized to benzoic acid.

Key concepts

Non-Enolizable Aldehydes

Non-enolizable aldehydes play a crucial role in the Cannizzaro reaction. To understand why, let's start by exploring the term **non-enolizable**. Aldehydes can differ based on the presence of an alpha hydrogen, a hydrogen atom adjacent to the carbonyl group. Non-enolizable aldehydes do not have this alpha hydrogen. Because of this lack, these aldehydes cannot form enols, a specific tautomer or isomer where the carbonyl group becomes an enol group. In non-enolizable aldehydes: - There is no hydrogen atom next to the carbonyl group. - As such, they are impermeable to transformations through enolate formation. Benzaldehyde is a classic example of such an aldehyde. This makes it a perfect candidate for the Cannizzaro reaction, as it bypasses alternate reaction pathways involving enolization.

Redox Reaction

A redox reaction is a chemical reaction involving the transfer of electrons between two species. It includes both reductions, a gain of electrons, and oxidation, a loss of electrons. In the context of the Cannizzaro reaction, it is a redox reaction occurring simultaneously between two molecules of a non-enolizable aldehyde in a basic environment. Key Characteristics of the Cannizzaro Redox Reaction: - One aldehyde molecule undergoes reduction to become an alcohol - Simultaneously, the other aldehyde molecule is oxidized to form a carboxylic acid In the case of benzaldehyde in a Cannizzaro reaction: - Benzyl alcohol is formed through the reduction process. - Benzoic acid is produced via oxidation. This duality illustrates the essence of redox reactions where both electron loss and gain occur together, balancing the equation between reactants and products.

Organic Chemistry

Organic chemistry is a branch of chemistry that focuses on the study of carbon-containing compounds, their properties, structures, and reactions. Within the realm of organic chemistry, the Cannizzaro reaction is a fascinating transformation mainly involving support from basic conditions and non-enolizable aldehydes. The Importance of Organic Chemistry in Understanding Cannizzaro Reaction: - Deepens our understanding of how carbon-based molecules react and transform. - Provides the foundation for predicting reaction products and understanding mechanism pathways. In the realm of the Cannizzaro reaction, organic chemistry principles allow chemists to assess: - Molecular structures to determine if aldehydes are non-enolizable. - Possible reaction outcomes such as alcohol and acid formation, emphasizing aldehyde behavior in specific reactions like Cannizzaro.

Alpha Hydrogen

Alpha hydrogen refers to the hydrogen atoms that are attached to the carbon atom immediately adjacent to a carbonyl group. This hydrogen's presence or absence significantly influences an aldehyde's reactivity, particularly in the context of various reactions. Characteristics of Alpha Hydrogen in Aldehydes: - Aldehydes with alpha hydrogen can undergo reactions involving enol or enolate ion formation. - When such hydrogen is absent, as with non-enolizable aldehydes like benzaldehyde, the molecule is more vulnerable to specific types of reactions like the Cannizzaro reaction. Understanding Alpha Hydrogen: - Crucial for determining the pathway an aldehyde will take in reactions. - Helps determine whether an aldehyde will resist or engage in reactions that typically require enolizable protons. In summary, the absence of alpha hydrogen in benzaldehyde explains its suitability for the Cannizzaro reaction, ensuring no alternate pathways like aldol condensations interfere with the process.