Question

In a reaction between ammonia and glutaraldehyde, what is the major product? \((A)\) An imine (B) \(\quad\) A cyanohydrin \((C)\) A semicarbazone (D) \(\quad\) A hydrazone

Short answer

An imine

Step-by-step solution

Understand the Reactants

Identify the chemical species involved in the reaction: ammonia (NH₃) and glutaraldehyde (OHC(CH₂)₃CHO).

Identify Possible Reaction Types

Determine the types of reactions ammonia typically undergoes with carbonyl compounds. Ammonia usually reacts with aldehydes or ketones to form imines.

Recall Reaction Mechanism

In the reaction between an aldehyde and ammonia, the ammonia attacks the carbonyl carbon to form a tetrahedral intermediate, which then loses water to form an imine.

Check Given Options

Compare the products given in the options. Only one matches the type of product formed: an imine.

Determine the Major Product

Conclude from the reaction mechanism and the given options that the major product of the reaction between ammonia and glutaraldehyde is an imine.

Key concepts

Imine Formation

Imine formation is a fundamental reaction in organic chemistry that involves the conversion of an aldehyde or ketone into an imine. This reaction typically occurs when an aldehyde or ketone reacts with a primary amine, such as ammonia (NH₃). The process begins with the nucleophilic attack of the amine on the carbonyl carbon of the aldehyde or ketone. This step forms a tetrahedral intermediate.
Next, the intermediate undergoes a dehydration step, where a molecule of water is removed. This results in the formation of a double bond between the nitrogen and the carbon, producing an imine.
In the case of our exercise, glutaraldehyde is the aldehyde, and ammonia serves as the primary amine. This reaction will yield an imine as the major product. Understanding this mechanism helps in predicting and controlling the outcome of similar reactions in synthetic organic chemistry.

Aldehyde Reactivity

Aldehyde reactivity is crucial to understanding many organic reactions, including imine formation. Aldehydes are characterized by a carbonyl group (C=O) where the carbon is bonded to at least one hydrogen atom. The carbonyl carbon is electrophilic, meaning it has a partial positive charge and is prone to nucleophilic attack.
Because of this electrophilic nature, aldehydes readily react with nucleophiles like ammonia. The lone pair of electrons on the nitrogen in ammonia can attack the electrophilic carbonyl carbon, initiating the formation of a tetrahedral intermediate.
This high reactivity of aldehydes compared to ketones is due to less steric hindrance and a greater positive charge on the carbonyl carbon, making aldehydes very active participants in nucleophilic addition reactions. In the glutaraldehyde and ammonia reaction, this property ensures the formation of an imine as the major product.

Reaction Mechanism

Understanding the reaction mechanism is key to predicting the products of organic reactions. Let's break down the mechanism of the reaction between glutaraldehyde and ammonia:
First, the nitrogen of the ammonia, which carries a lone pair of electrons, attacks the carbonyl carbon of the aldehyde. This is a nucleophilic addition step, leading to the formation of a tetrahedral intermediate.
Second, this intermediate undergoes a series of proton transfer steps and eventually loses a water molecule through a dehydration step. The departure of water helps to stabilize the intermediate, forming a double bond between the nitrogen and the carbon. The end product is an imine.
Throughout this process, the role of ammonia is to provide the nucleophilic nitrogen that attacks the electrophilic carbonyl carbon, while the aldehyde's role is to act as the electrophile. Understanding these steps allows us to predict that the major product when glutaraldehyde reacts with ammonia is indeed an imine.