Problem 96 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{NH}_{2} \frac{\mathrm{NaNO}_{2}}{\mathrm{HCl}} \rightarrow[\mathrm{P}] ;\) Products of the reaction are: (a) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\) (b) Et-Cl (c) \(\mathrm{Et}-\mathrm{C}-\mathrm{H}\) (d) \(\mathrm{Et}-\mathrm{ONO}\)

Step-by-Step Solution

Answer

The product of the reaction is ethanol, \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\).

Step 1: Understand the Reaction

The given reaction starts with ethylamine (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{NH}_{2}\)) that reacts with sodium nitrite (NaNO₂) in the presence of hydrochloric acid (HCl). This type of reaction is known as diazotization.

Step 2: Diazotization Process

During diazotization, primary aliphatic amines like ethylamine react with nitrous acid (HNO₂), which is formed in situ by the reaction of NaNO₂ and HCl, to form a diazonium salt. However, aliphatic diazonium salts are unstable and decompose, often releasing nitrogen gas.

Step 3: Identify the Products

For an aliphatic amine like ethylamine, the diazonium ion decomposes to form a carbocation. In this specific reaction, the carbocation formed is an ethyl cation (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}^+\)). This cation can react with various species in the solution.

Step 4: Formation of the Alcohol

The ethyl cation (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}^+\)) can react with water present in the acidic medium to form ethanol (\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\)). This is a typical outcome for reactions of this nature.

Key Concepts

Diazotization

Understanding diazotization is key when diving into organic chemistry reactions involving amines. Diazotization involves converting primary amines into diazonium salts. This reaction is crucial because it acts as a gateway to many diverse and useful synthetic pathways.

To begin the diazotization process, you first need a primary amine like ethylamine, which reacts with nitrous acid. Nitrous acid isn't typically available as a reagent but is instead generated in situ. This means it's produced directly in the reaction mixture, often by mixing sodium nitrite (NaNO₂) with a strong acid like hydrochloric acid (HCl).

• Primary amine + Nitrous acid → Diazonium salt + Water
• The byproduct release of nitrogen gas (N₂) is another common feature of this process.

Diazonium salts can be quite reactive because they tend to be unstable, especially in the case of aliphatic amines.

Aliphatic Amines

Aliphatic amines like ethylamine are simple compounds composed of nitrogen attached to carbon chains. These compounds feature prominently in organic chemistry due to their reactivity.

Aliphatic amines contain a nitrogen atom bonded to one or more alkyl groups. The most straightforward example, being methylamine, features a single nitrogen bound to a methyl group. Ethylamine (CH₃-CH₂-NH₂), used in our reaction, has an ethyl group attached to nitrogen.

• Less bulky than aromatic amines.
• Highly reactive, serving as ideal candidates for diazotization.

Understanding aliphatic amines’ basic structure and reactivity assists in predicting and controlling their behavior in various chemical environments.

Carbocation Formation

The step from diazonium salt to carbocation is pivotal in understanding many organic reactions. The transition involves the breaking down of a diazonium salt (though unstable), which leaves behind a carbocation.

For ethylamine's reaction, this breakdown results in a simple yet fascinating convertible—a charged intermediate known as carbocation, specifically the ethyl cation (CH₃-CH₂⁺).

• Carbocations are positively charged.
• Extremely reactive owing to this positive charge.
• Prone to react quickly with surrounding molecules in a solution, seeking to stabilize themselves.

In this reaction, carbocation formation provides an intermediate crucial for the creation of final products such as ethanol.

Ethanol Formation

The formation of ethanol is a classic outcome of an aliphatic amine diazotization reaction. This occurs when the carbocation, formed from the unstable diazonium salt, interacts with molecules in its environment.

The ethyl cation's reactivity plays a significant role here, as it easily reacts with water present in the solution.

• Ethyl cation (CH₃-CH₂⁺) + Water (H₂O) → Ethanol (CH₃-CH₂-OH)
• The reaction typically requires an acidic medium for stability and proper progress.

Understanding this process highlights how simple amines can transform into alcohols via a well-orchestrated chemical dance, making it an exciting area of study in organic chemistry.