Problem 105 - A Complete Resource Book in Chemistry for JEE Main

Question

When a mixture of primary, secondary is treated with nitrous acid then the products given by them are respectively (a) Nitrosoamine and alcohol (b) Alcohol and nitrosoamine (c) Nitroalkane and nitrosoamine (d) Nitrosoamine and nitrite salts

Step-by-Step Solution

Answer

(b) Alcohol and nitrosoamine

Step 1: Understanding the Reaction

When we treat amines with nitrous acid, we're looking at the reactions of two types of amines – primary and secondary. Primary amines react with nitrous acid to form alcohols, while secondary amines result in the formation of nitrosoamines.

Step 2: Identifying Primary Amines Reaction

Primary amines react with nitrous acid ( ext{HNO}_2) to form an unstable diazonium salt, which then decomposes to produce an alcohol. The general reaction is: \[ R-NH_2 + HNO_2 ightarrow R-N_2^+ + H_2O ightarrow R-OH + N_2 \] The end product of the reaction is an alcohol.

Step 3: Identifying Secondary Amines Reaction

Secondary amines, when treated with nitrous acid, form nitrosoamines. This reaction proceeds without the formation of a diazonium salt, leading directly to the formation of an N-nitroso compound. The chemical reaction is: \[ R_2NH + HNO_2 ightarrow R_2N-NO + H_2O \] Thus, the end product of the reaction of secondary amines is nitrosoamine.

Step 4: Selecting the Appropriate Answer

From our analysis: primary amine produces an alcohol and secondary amine produces a nitrosoamine when treated with nitrous acid. Therefore, the correct answer based on the given options is: (b) Alcohol and nitrosoamine.

Key Concepts

Primary Amines

Primary amines are organic compounds characterized by the presence of a nitrogen atom bonded to one alkyl or aryl group and two hydrogen atoms. The general structure can be identified as \( R-NH_2 \). When primary amines interact with nitrous acid (\( HNO_2 \)), a unique transformation takes place:

• An unstable diazonium salt is first formed.
• This diazonium salt does not linger due to its instability and swiftly decomposes.
• The decomposition leads to the formation of an alcohol.

The reaction can be represented as follows: \[R-NH_2 + HNO_2 \rightarrow R-N_2^+ + H_2O \rightarrow R-OH + N_2\]This transformation is crucial for organic synthesis, emphasizing the rich chemistry primary amines exhibit under specific conditions. Essentially, the shift from a primary amine to an alcohol highlights the influence of electron deficiency in the diazonium ion, prompting the nitrogen gas release and resulting in alcohol formation.

Secondary Amines

Secondary amines, containing the general structure \( R_2NH \), are characterized by having the nitrogen atom bonded to two alkyl or aryl groups. When these amines are treated with nitrous acid, a different kind of product emerges:

• Unlike primary amines, secondary amines do not form diazonium salts.
• Instead, they proceed to form nitrosoamines directly.

This reaction can be symbolized as:\[R_2NH + HNO_2 \rightarrow R_2N-NO + H_2O\]The nitrosoamine formation involves the nitrosation of the secondary amine. This process occurs due to the migration of the nitroso group \( (-NO) \) to the nitrogen atom, forming a stable N-nitroso compound. Nitrosoamines have significant applications in various chemical industries and serve as critical intermediates in many synthetic pathways.

Alcohol Formation

Alcohol formation from primary amines is a fascinating aspect of organic reactions. When primary amines are treated with nitrous acid, the transient formation of diazonium salts is a crucial intermediary step. These salts don't exist for long due to their inherent instability, but their quick breakdown leads to alcohol production.

• This entire reaction leads to the transformation of amines into corresponding alcohols.
• Such reactions are vital, especially considering they liberate nitrogen gas \( (N_2) \), a process that helps drive the reaction to completion.

The alcohol produced retains the carbon backbone of the original amine, but it now possesses a hydroxyl group in place of the nitrogen-containing group. This transformation plays a pivotal role in synthetic organic chemistry, enabling the conversion of nitrogen-containing compounds into widespread alcohol derivatives with varied applications.

Nitrosoamine Formation

Nitrosoamines are key products formed from the reaction of secondary amines with nitrous acid. They are an intriguing set of compounds owing to their structural uniqueness and chemical behavior.

• In the presence of nitrous acid, a secondary amine converts neatly into a nitrosoamine without intermediate diazonium formation.
• The nitroso group provides these compounds with characteristic stability and unique properties.

The reaction can be characterized by its simplicity yet effectiveness in converting amines into nitroso derivatives:\[R_2NH + HNO_2 \rightarrow R_2N-NO + H_2O\]Nitrosoamines have earned attention for their discoverable properties and applications in the manufacture of dyes, agricultural chemicals, and rubber products. Their understanding and handling are vital in organic reaction strategies, highlighting their significance in bridging the synthesis of more complex chemical structures.