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 trimethylamine, \((CH_3)_3N\), which is option (d).

Step 1: Identify the compound

The given compound is tetramethylammonium hydroxide, \[(CH_3)_4NOH\]. It consists of a quaternary ammonium cation \((CH_3)_4N^+\) and a hydroxide anion \((OH^-)\).

Step 2: Determine the decomposition products

When tetramethylammonium hydroxide is heated, it decomposes. The typical decomposition process results in the formation of trimethylamine and methanol:\[(CH_3)_4NOH \rightarrow (CH_3)_3N + CH_3OH\].

Step 3: Identify the organic compound among the options

From the decomposition reaction,\[(CH_3)_3N\] is trimethylamine, present as an option.The options are:(a) \(C_2H_5NH_2\) (b) \((CH_2)_3N\) (c) \(CH_3NH_2\) (d) \((CH_3)_3N\) Thus, the correct answer is option (d).

Key Concepts

Decomposition Reactions

Decomposition reactions are an essential part of organic chemistry. They involve breaking down a single compound into two or more products. These reactions often require energy, like heat, to occur and are characterized by their simple form:

• AB → A + B

In our exercise, the compound tetramethylammonium hydroxide \((CH_3)_4NOH\) undergoes a decomposition reaction when heated. Here it breaks down into trimethylamine \((CH_3)_3N\) and methanol \(CH_3OH\). This is a common pattern for quaternary ammonium compounds, where the cation dissociates, releasing a small molecule like methanol.
This process is heavily influenced by conditions such as temperature. Sometimes catalysts can be used to lower the energy required for the decomposition. Understanding the nature of these reactions is crucial as they can provide insights into the stability of compounds and their behavior under different conditions.

Quaternary Ammonium Compounds

Quaternary ammonium compounds are a fascinating class of molecules in organic chemistry. These compounds have a positively charged nitrogen atom, making them quaternary because the nitrogen is attached to four carbon-containing groups. The general formula can be represented as \((R_1R_2R_3R_4)N^+\). It is this unique structure that lends these compounds various properties and applications. They are often used as surfactants and disinfectants.
In the decomposition reaction we studied, \((CH_3)_4NOH\) is an example of a quaternary ammonium compound. Here, each R group is a methyl group \((CH_3)\), leading to a compound known as tetramethylammonium. When exposed to heat, these quaternary ammonium compounds often break down to release stable products like trimethylamine. They are stable under normal conditions but can dissociate under specific triggers like heat.

Trimethylamine

Trimethylamine is an important organic compound that often arises from the decomposition of quaternary ammonium compounds. Its structure consists of three methyl groups bonded to a nitrogen atom \((CH_3)_3N\). Trimethylamine is a common product of decomposition and plays a significant role in various chemical processes.
In practice, trimethylamine is known for its fishy odor and is used in industrial chemistry to produce a range of products, including agricultural chemicals and pharmaceuticals. Understanding its formation and properties is vital in controlling and predicting the outcomes of many organic reactions. Its appearance in our decomposition example is typical, as trimethylamine represents a decomposed product due to the breaking of the tetramethylammonium structure. It is interesting to note how decomposition leads to simpler and often more easily manipulated substances like trimethylamine, showing the importance of organic reaction mechanisms.