Question

Compound \(\mathrm{R}+\) Compound \(\mathrm{T} \quad \mathrm{NaBH}_{\mathrm{S} \mathrm{CN}}{\longrightarrow}\) Product The product is: (A) \(1^{\circ}\) amine (B) \(2^{\circ}\) amine (C) \(3^{\circ}\) amine (D) Quaternary amine

Short answer

The final product of the given reaction will be either a \(2^\circ\) amine (B) when starting with a \(1^\circ\) amine in compound R, or a \(3^\circ\) amine (C) when starting with a \(2^\circ\) amine in compound R. It will not be a \(1^\circ\) amine or quaternary amine.

Step-by-step solution

Identify the Reducing Agent

Here, the reducing agent used is Sodium Cyanoborohydride (NaBH3CN). It is a mild reducing agent that can selectively reduce imines and iminium ions, but not other groups or molecules such as carbonyl compounds, esters, or nitriles.

Determine the Reaction: R and T

Since NaBH3CN selectively reduces imines and iminium ions, the starting compounds R and T must form an imine or iminium ion upon reaction to produce the amine product. Thus, compounds R and T should be an amine (primary or secondary) and a carbonyl compound (aldehyde or ketone) to form an iminium ion upon reaction.

Formation of Iminium Ion

When an amine reacts with a carbonyl compound, the nitrogen atom in the amine attacks the carbonyl carbon, forming an imine or iminium ion. The reaction proceeds through the following steps: 1. Nucleophilic addition of the nitrogen atom to the carbonyl carbon of the aldehyde or ketone. 2. Proton transfer, followed by the elimination of water.

Reduction of Iminium Ion to Amine

Once the iminium ion is formed, the NaBH3CN can selectively reduce it to an amine by transferring a hydride ion (H-) to the iminium carbon. This leads to the formation of a new amine group.

Determining the Degree of Amine

To determine the degree of amine in our product, we need to consider the starting amine in compound R. Since the reaction requires the formation of an iminium ion, the starting amine should be either primary (1°) or secondary (2°). The carbonyl compound in compound T will contribute to the degree of the amine in the product: 1. If R = 1° amine and T = carbonyl compound, then the product will be a 2° amine. 2. If R = 2° amine and T = carbonyl compound, then the product will be a 3° amine.

Conclusion

Based on the analysis of the reaction, the final product will be a 2° amine (B) when starting with a 1° amine in compound R, or a 3° amine (C) when starting with a 2° amine in compound R. So, we can conclude that the product will be either 2° amine or 3° amine, but not a 1° amine or quaternary amine.

Key concepts

Reducing Agents

Reducing agents are substances that donate electrons to another compound, resulting in the reduction of that compound. In chemical reactions involving amines, reducing agents play a crucial role.
A commonly used reducing agent in amine synthesis is Sodium Cyanoborohydride (\( \text{NaBH}_3\text{CN} \)).

• This agent is known for being mild and selective, which is a significant advantage during reduction reactions.
• Sodium Cyanoborohydride does not reduce every functional group; it is tailored for imines and iminium ions, avoiding reductions in carbonyl groups, esters, or nitriles.

This selective reduction is key in synthesizing specific amines without affecting other parts of the molecule.

Imine Formation

Imine formation occurs when an amine reacts with a carbonyl compound, such as an aldehyde or ketone. This process involves several key steps:

• The nitrogen atom from the amine performs a nucleophilic attack on the carbonyl carbon of the carbonyl compound.
• This is followed by a proton transfer and the elimination of water, leading to the generation of an imine or iminium ion.

Imines are important intermediates in many organic reactions, serving as a bridge to further transformations. The ability to form an imine is crucial in the synthesis of more complex molecules, such as secondary and tertiary amines.

Iminium Ion Reduction

Once an iminium ion is formed, it can be reduced to form an amine. This step involves the selective reduction by a reducing agent like Sodium Cyanoborohydride.
The mechanism involves transferring a hydride ion (\( \text{H}^- \)) from the reducing agent to the iminium carbon, which creates a new amine group.

• This process is central to efficient amine synthesis, allowing the conversion of multiple types of starting materials into valuable amines.
• The selective nature of iminium ion reduction is beneficial, as it targets specific intermediates without affecting other parts of the molecule.

Ultimately, the success of iminium ion reduction lies in its ability to generate amines with precision and minimal by-products.

Amine Classification

Amines are classified based on the number of organic substituents attached to the nitrogen atom. Understanding these classifications helps in predicting the outcomes of synthesis reactions. The main classes of amines include:

• Primary (1°) amines, where the nitrogen is bonded to one alkyl or aryl group.
• Secondary (2°) amines, with two organic groups attached to the nitrogen.
• Tertiary (3°) amines, with three groups attached to the nitrogen.
• Quaternary ammonium compounds, where the nitrogen carries a positive charge due to four bonds to organic groups.

In the context of reduction reactions, it's crucial to recognize how starting materials like primary or secondary amines can influence the final amine product. Understanding these classifications assists chemists in designing effective synthetic pathways that lead to the desired compound.