Problem 56 - A Complete Resource Book in Chemistry for JEE Main

Question

The common statement(s) between Curtuis and Hoffmann degradation is/are 1\. Both involve nitrene reaction intermediate 2\. Both involve intramolecular alkyl shift 3\. Curtius reaction gives primary amine while Hoffimann degradation gives secondary amine 4\. Curtius reaction uses \(\mathrm{NaN}_{3}\) while Hofmann degradation uses \(\mathrm{NaOBr}\) (a) \(1,2,3\) (b) \(1,2,4\) (c) \(2,3,4\) (d) \(1,3,4\)

Step-by-Step Solution

Answer

The correct answer is (b) 1,2,4.

Step 1: Analyze the reactions

The Curtius rearrangement and Hofmann degradation are both chemical reactions used to transform acyl azides and amides, respectively, into amines. In Curtius rearrangement, the acyl azide is typically heated or treated with heat or light to facilitate the rearrangement, resulting in the formation of a nitrene intermediate and eventually a primary amine. Hofmann degradation involves the reaction of an amide with a halogen in the presence of a strong base to yield a primary amine and can also involve a nitrene intermediate.

Step 2: Check for Nitrene Intermediate

Both Curtius and Hofmann reactions are known to proceed via the formation of a nitrene intermediate. Thus, statement 1 is true: both reactions involve a nitrene reaction intermediate.

Step 3: Evaluate Intramolecular Alkyl Shift

The Curtius reaction and Hofmann degradation do not typically involve an intramolecular alkyl shift as part of their major reaction pathway. Therefore, statement 2 is false for both reactions.

Step 4: Examine Amines Produced

The Curtius reaction typically results in the formation of a primary amine. Hofmann degradation also yields a primary amine, not a secondary one. Therefore, statement 3 is false because Hofmann degradation does not produce a secondary amine.

Step 5: Identify Reagents Used

Curtius reaction involves the use of sodium azide (NaN_{3}), while Hofmann degradation involves the use of sodium hypobromite (NaOBr). This makes statement 4 true.

Step 6: Determine Correct Option

From the previous analysis, we found that statements 1 and 4 are true, while statements 2 and 3 are false. Therefore, the correct option is the one that includes both 1 and 4, which is option (d) 1,3,4.

Key Concepts

Curtius Rearrangement

The Curtius rearrangement is a fascinating transformation in organic chemistry. It involves converting an acyl azide into a primary amine, usually by applying heat or irradiating with light. During this process, a nitrene intermediate is formed. This is a crucial step as the nitrene is highly reactive and facilitates the rearrangement. The reaction can be summarized in a few key steps:

• Start with an acyl azide.
• Apply heat or light to promote the rearrangement.
• Form a nitrene intermediate.
• Rearrange into an isocyanate intermediate.
• Hydrolyze to yield a primary amine.

This rearrangement is valuable in synthesizing amines from simpler organic compounds, and understanding this process allows chemists to design reactions that transition smoothly through such intermediates.

Hofmann Degradation

The Hofmann degradation, also referred to as the Hofmann rearrangement, is another critical reaction in organic chemistry. It transforms an amide into a primary amine using a halogen and a strong base, such as sodium hypobromite (NaOBr). Similar to the Curtius rearrangement, it also proceeds through a nitrene intermediate. Here is how the Hofmann degradation generally progresses:

• Start with an amide as the substrate.
• Introduce a halogen and strong base, like NaOBr.
• Form a nitrene intermediate.
• Perform a rearrangement to an isocyanate.
• Hydrolyze the isocyanate to achieve a primary amine.

This methodology is especially useful in expanding carbon chains in amine synthesis, offering efficient pathways for creating new compounds with desired features.

Nitrene Intermediate

A nitrene intermediate is a highly reactive, nitrogen-centered species crucial in numerous organic reactions, including Curtius rearrangement and Hofmann degradation. Understanding the nature of nitrenes helps chemists predict and control the outcomes of these transformations. Key characteristics of nitrenes include:

• Nitrenes typically have six valence electrons, making them electron-deficient and highly reactive.
• They can exist in two spin states: singlet and triplet, with singlet states usually being more reactive.
• Nitrenes exhibit unique reactivity patterns, enabling the rearrangement and formation of desired products, such as amines.

These intermediates are pivotal because they facilitate complex rearrangements that would be less feasible without their reactivity and orientation towards forming new bonds.

Reaction Mechanisms

Reaction mechanisms are the step-by-step sequences of elementary reactions by which an overall chemical change occurs. In the context of organic chemistry, mechanisms help us understand how reactants transition into products, especially in complex transformations like Curtius rearrangement and Hofmann degradation. Understanding these mechanisms involves:

• Recognizing the starting materials and end products.
• Identifying intermediates, like nitrenes, which bridge reactants to products.
• Details on bond breaking and forming through each step, often depicted with curved arrows in reaction diagrams.
• Considering factors such as temperature, solvent, and catalysts that influence the mechanism's pathway.

By mastering reaction mechanisms, chemists can predict reaction outcomes, optimize conditions, and innovate new synthetic routes to create desired molecules effectively and efficiently.