Problem 14 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is formed when \(\left(\mathrm{CH}_{3}\right)_{4} \mathrm{NOH}\) is heated? (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}\) (b) \(\left(\mathrm{CH}_{2}\right)_{3} \mathrm{~N}\) (c) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) (d) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\)

Step-by-Step Solution

Answer

The compound formed is \((\mathrm{CH}_{3})_{3} \mathrm{~N}\) (option d).

Step 1: Analyze the given compound

The compound \((\mathrm{CH}_{3})_{4} \mathrm{NOH}\) is a hydroxide of tetramethylammonium. It can be represented in a more familiar form as \((CH_3)_4N^+OH^-\). This compound is a quaternary ammonium hydroxide, which is unstable at high temperatures.

Step 2: Decomposition of quaternary ammonium hydroxide

When heated, quaternary ammonium hydroxides generally decompose into the corresponding tertiary amine and water. In this case, \((\mathrm{CH}_{3})_{4} \mathrm{NOH}\) will decompose into a tertiary amine and water.

Step 3: Identify the tertiary amine

For the compound \((\mathrm{CH}_{3})_{4} \mathrm{NOH}\), the likely decomposition reaction is: \[(\mathrm{CH}_{3})_{4} \mathrm{NOH} \rightarrow \mathrm{(CH_3)_3N} + \mathrm{H_2O}\]. This indicates that the resulting amine is \((\mathrm{CH}_{3})_{3} \mathrm{~N}\), which corresponds to trimethylamine.

Step 4: Match to the given options

Compare the product from the decomposition \((\mathrm{CH}_{3})_{3} \mathrm{~N}\) with the multiple choice options. Match \((\mathrm{CH}_{3})_{3} \mathrm{~N}\) to option (d). This is our answer.

Key Concepts

Decomposition Reactions

A decomposition reaction involves breaking down a single compound into two or more simpler substances, often as a result of heating or exposure to energy. In chemistry, these reactions are generally associated with compounds that are unstable under certain conditions.

For instance, quaternary ammonium hydroxides such as tetramethylammonium hydroxide \((\mathrm{CH}_3)_4\mathrm{NOH}\) become unstable when heated. This causes them to decompose. Here, this specific quaternary ammonium hydroxide decomposes into a tertiary amine and water when heat is applied:
\((\mathrm{CH}_3)_4\mathrm{NOH} \rightarrow (\mathrm{CH}_3)_3\mathrm{N} + \mathrm{H_2O}\)\.

Each decomposition reaction follows a path dictated by the stability of intermediate products and the energy required to break the chemical bonds. In this example, the formation of a stable tertiary amine, trimethylamine \((\mathrm{CH}_3)_3\mathrm{N})\), is preferred because it offers a simpler molecular structure.

Tertiary Amines

Tertiary amines are a class of amines where the nitrogen atom is bonded to three alkyl or aromatic groups, which provides stability and distinct properties. In the context of decomposition reactions, they are often the end product when quaternary ammonium compounds break down.

An example of this is the compound trimethylamine \((\mathrm{CH}_3)_3\mathrm{N})\), obtained from the decomposition of tetramethylammonium hydroxide. Tertiary amines like trimethylamine possess a lone pair of electrons on the nitrogen atom, contributing to its basicity. They are crucial in organic synthesis and industrial applications.

The following are general traits of tertiary amines:

• They lack hydrogen atoms directly bonded to nitrogen, unlike primary and secondary amines, which gives them different reactivity patterns.
• Tertiary amines tend to form weaker hydrogen bonds than primary and secondary amines.
• They are often used to produce quaternary ammonium salts when reacted with alkyl halides.

These properties make tertiary amines like trimethylamine unique and versatile in different chemical contexts.

Chemical Stability

Chemical stability refers to the ability of a compound to remain unchanged under normal conditions. This concept involves understanding how external factors, such as temperature and pH, can influence a chemical's propensities to decompose or react further.Quaternary ammonium hydroxides, such as tetramethylammonium hydroxide \((\mathrm{CH}_3)_4\mathrm{NOH})\), exhibit lesser chemical stability when subjected to heat. In this scenario:

• High temperatures provide energy that disrupts the chemical bonds.
• The hydroxide breakdown leads to water and a more stable configuration of a tertiary amine.

The driving force behind such decomposition is often the formation of products that are more chemically stable than the initial reactant. Factors such as the removal of hydroxide ions in this example result in increased stability for the tertiary amine, hence completion of the reaction.Understanding chemical stability helps chemists predict the types of reactions that will occur under certain conditions, which in turn aids in the safe and efficient design of chemical processes. This knowledge is crucial for developing applications in industries ranging from pharmaceuticals to materials science.