Question

Hydration of an aldehyde is also catalyzed by hydroxide ion. Propose a mechanism for the reaction.

Short answer

Mechanism of base catalyzed hydrolysis

Step-by-step solution

Reactions of aldehydes

Organic compounds that contain a –CHO functional group are called aldehydes. The C-O bond in an aldehyde is highly polar, which makes the alpha carbon electrophilic. The oxygen atom contains lone pairs and is therefore, nucleophilic.

The carbonyl group is attached to a hydrogen atom and an alkyl group in an aldehyde. Aldehydes mainly undergo reactions due to the electrophilicity of carbonyl carbon. Aldehydes can form enolate ions which further increases the reactivity of carbonyl carbon.

Hydrolysis of aldehyde

The reaction of aldehydes with water to form the hydrate is called hydrolysis. The hydrolysis reaction can be acid-catalyzed and base-catalyzed. These catalysts active the carbonyl and make the carbonyl carbon more electrophilic.

The catalyst is regenerated at the end of the reaction. Acid catalysts activate the carbonyl by donating a proton to the oxygen atom of the carbonyl. The base catalysts directly attach to the electrophilic carbon.

Base catalyzed hydrolysis of aldehyde

Strong bases like hydroxide ions can activate the carbonyl by attacking the electrophilic carbon centre. This produces a negative charge in the oxygen atom.

The negative charged oxygen atom abstracts proton from the water molecule forming the hydride.

The hydroxide ion is regenerated at the end of the reaction. The reaction can be given as:

Mechanism of base catalyzed hydrolysis