Problem 88 - A Complete Resource Book in Chemistry for JEE Main

Question

Nitrosoamines \(\left(\mathrm{R}_{2} \mathrm{~N}-\mathrm{N}=\mathrm{O}\right)\) are insoluble in water. On heating them with conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\). They give secondary amines. The reaction is called (a) Fries reaction (b) Etard reaction (c) Lieberman nitroso reaction (d) Perkin reaction

Step-by-Step Solution

Answer

(c) Lieberman nitroso reaction

Step 1: Understand the Question

We need to identify which reaction, from the given options, describes the process in which nitrosoamines are heated with conc. \( \mathrm{H}_{2} \mathrm{SO}_{4} \) to yield secondary amines.

Step 2: Recall Reaction Types

Fries reaction is generally related to the acylation of phenols. Etard reaction involves the oxidation of toluene to benzaldehyde. Perkin reaction involves the condensation of an aromatic aldehyde with acetic anhydride. Liebermann nitroso reaction involves the reaction of nitrosoamines with sulfuric acid to give secondary amines.

Step 3: Match Details

The description of the reaction where nitrosoamines are converted into secondary amines using conc. \( \mathrm{H}_{2} \mathrm{SO}_{4} \) aligns with the Liebermann nitroso reaction.

Key Concepts

Nitrosoamines

Nitrosoamines are a class of organic compounds with the general formula \( \mathrm{R}_{2} \mathrm{~N}-\mathrm{N}=\mathrm{O} \). They are characterized by their nitroso group \( (\mathrm{-N=O}) \). One of their standout characteristics is that they are typically insoluble in water. This insolubility is particularly significant when considering reactions in aqueous environments. These compounds are sensitive to reducing and acidic environments, which plays a role in their reactivity in various chemical reactions. In the Liebermann nitroso reaction, nitrosoamines react in an acidic medium, such as concentrated sulfuric acid, leading to their conversion into secondary amines. Their instability and reactivity to acidic conditions make them fascinating subjects for studying organic transformations.

Secondary Amines

Secondary amines are organic compounds where a nitrogen atom is attached to two alkyl or aryl groups and one hydrogen atom. Their general formula is \( \mathrm{R}_{2}\mathrm{NH} \). This structure allows secondary amines to participate in various chemical reactions due to the presence of the lone pair of electrons on the nitrogen. They are versatile intermediates in organic synthesis, and their synthesis or transformation often involves the use of reactive conditions or reagents. For instance, in the case of the Liebermann nitroso reaction, nitrosoamines are converted into secondary amines when subjected to strong acidic conditions such as concentrated sulfuric acid. The electron-rich nature of the nitrogen in secondary amines makes them nucleophilic, which allows them to undergo further functional group transformations, enhancing their utility in organic chemistry.

Concentrated Sulfuric Acid

Concentrated sulfuric acid \((\mathrm{H}_2\mathrm{SO}_4)\) is a highly potent acid known for its dehydrating properties and strong acidic nature. It is widely used in laboratory and industrial applications due to its ability to protonate reacting species, thereby facilitating a wide range of reactions. In the context of the Liebermann nitroso reaction, concentrated \( \mathrm{H}_2\mathrm{SO}_4 \) serves as the catalyst and medium for converting nitrosoamines to secondary amines. It provides the acidic environment necessary for the reaction to proceed, breaking the nitrosoamine bond and forming secondary amines. This transformation showcases the role of sulfuric acid as more than just a proton donor but also as a key driver in rearranging chemical structures. Care must be taken when handling concentrated sulfuric acid, given its corrosive nature and potential to cause chemical burns.