Problem 7 - Chemistry in 30 days

Question

The reaction gives $$ \mathrm{CH}_{3} \mathrm{CONH}_{2} \frac{\mathrm{NaOBr}}{\mathrm{H}_{2} \mathrm{O}} $$ (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{CN}\) (d) \(\mathrm{CH}_{1} \mathrm{Br}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{CH}_{3}\mathrm{NH}_{2}\)

Step 1: Identify the Reaction Type

The given reaction involves the use of NaOBr and water, which indicates a Hofmann rearrangement. This is a well-known reaction in organic chemistry where an amide is converted into an amine with one fewer carbon atom.

Step 2: Predict the Reaction Outcome

In a Hofmann rearrangement, the carbonyl group in the amide \(\mathrm{CH}_{3}\mathrm{CONH}_{2}\) is removed, leading to the formation of a primary amine with one less carbon. This typically transforms the molecule from acetylamide (1 carbon) to methylamine (1 carbon).

Step 3: Determine the Product

For the given amide \(\mathrm{CH}_{3}\mathrm{CONH}_{2}\), the application of the Hofmann rearrangement will break the C-N bond, lose a carbon as CO2, and produce a primary amine. The expected product is \(\mathrm{CH}_{3}\mathrm{NH}_{2}\).

Step 4: Select the Correct Option

The product of the reaction is \(\mathrm{CH}_{3}\mathrm{NH}_{2}\), which corresponds to option (b) in the given list of products.

Key Concepts

Organic Chemistry

Organic chemistry is a branch of chemistry focused on the structure, properties, composition, reactions, and synthesis of carbon-containing compounds. It encompasses a vast variety of compounds, including those that derive from living matter as well as synthetic ones. One important facet of organic chemistry is understanding the mechanisms of how molecules transform through chemical reactions.

Reactions such as the Hofmann rearrangement are crucial because they illustrate how certain functional groups in organic compounds can be modified or changed into other groups. These transformations are essential in the synthesis of complex molecules and have broad applications across pharmaceuticals, materials science, and biological chemistry.

The principles of organic chemistry also help us predict the types of reactions that might occur under certain conditions and the likely products that will result. In the realm of amine synthesis, understanding how an amide can transform into an amine provides insight into developing synthetic routes for creating specific compounds.

Amide to Amine Conversion

The conversion of an amide to an amine is a key transformation in organic chemistry, especially when using the Hofmann rearrangement. Amides are general compounds with the structure RCONH2, where R is an organic group. During this conversion, amides lose a carbon group and are transformed into primary amines.

This reaction is significant due to its ability to reduce the carbon chain length by one, which can be useful in various synthetic processes where simpler amines are needed. In the Hofmann rearrangement process, the nitrogen atom is drafted into the carbon-containing chain, while a carbon atom from the original amide is expelled as carbon dioxide.

The specific reaction often used is with NaOBr, a reagent that facilitates the rearrangement and excision of the carbon atom. This is especially useful for converting substances such as acetamide into simpler amines like methylamine, thereby altering both the structure and function of the original molecule.

Mechanism of Hofmann Rearrangement

The Hofmann rearrangement outlines a fascinating mechanism in organic chemistry which allows for the transformation of an amide into an amine with the concurrent loss of a carbon atom. The mechanism involves several steps that result in the net loss of the carbonyl group from the amide.

1. **Initial Stage**: The amide is treated with sodium hypobromite (NaOBr), initiating the deprotonation of the amide and formation of a bromamide intermediate.
2. **Rearrangement**: An intramolecular rearrangement occurs where the nitrogen atom migrates over to the carbon previously bonded to the carbonyl group. This step is facilitated by the formation of a nitrene intermediate.
3. **Decarboxylation**: The rearranged molecule loses carbon dioxide, resulting in a negatively charged nitrogen compound that quickly rearranges into an amine with the release of one carbon less than the starting amide.

This mechanism is vital for creating simpler amine compounds and is noted for its unique ability to alter the carbon skeleton of the starting material. Understanding each step is crucial for successfully applying the Hofmann rearrangement in synthetic organic chemistry.