Problem 188 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

A mixture of benzene and aniline can be separated by (a) alcohol (b) \(\mathrm{NaOH}\) (c) \(\mathrm{HCl}\) (d) hot water

Step-by-Step Solution

Answer

The mixture can be separated using \( \text{HCl} \).

Step 1: Analyze the Components

To solve this problem, we need to understand the properties of benzene and aniline. Benzene is a hydrocarbon, while aniline is a basic aromatic amine (due to the presence of an amino group, \( \text{NH}_2 \)). This means aniline is a weak base.

Step 2: Identify Suitable Reagents for Separation

We want a reagent that can react or interact with aniline but not benzene. - Alcohol is non-reactive with either component specifically. - \( \text{NaOH} \) is a strong base and will not affect the weakly basic aniline or benzene. - \( \text{HCl} \) is an acid that can protonate aniline, making it water-soluble.- Hot water can potentially help dissolve substances but will not selectively interact with either.

Step 3: Select the Best Option

Among the options, adding \( \text{HCl} \) will convert aniline to anilinium chloride, which is water-soluble, thus separating it from benzene, which remains insoluble. This allows for separation by transferring the aniline into an aqueous layer.

Key Concepts

Hydrocarbons

Hydrocarbons are pure compounds made solely of hydrogen and carbon atoms. These compounds serve as fundamental constituents of many other organic molecules. In organic chemistry, hydrocarbons are often considered the backbone of more complex structures.

Some common features include:

• Being typically non-polar, due to their symmetric structure.
• Insolubility in water but soluble in organic solvents.
• Having various forms like alkanes, alkenes, and alkynes.

Benzene is a classic example of a hydrocarbon known as an aromatic hydrocarbon. With the formula \( C_6H_6 \), benzene is characterized by a unique ring-like structure of carbon atoms. This configuration creates extensive delocalization of electrons, which contributes to its stability and low reactivity compared to other hydrocarbons. Benzene’s properties make it easily separable from other compounds, especially non-hydrocarbons.

Aromatic Amines

Aromatic amines are organic compounds comprised of an aromatic ring structure with an amino group \((−NH_2)\) attached. The presence of the amino group makes these compounds basic in nature. They also possess distinct characteristics compared to non-aromatic amines.

Some interesting properties include:

• The aromatic ring provides stability through resonance.
• The amino group acts as a basic site, able to accept protons.
• Aromatic amines typically appear in compounds like dyes and pharmaceuticals.

Aniline is a prime example of an aromatic amine. With its aromatic ring bonded to an amino group, it exhibits basic behavior. In separation processes, its ability to undergo protonation is useful. Protonation transforms aniline into anilinium, enabling it to shift from one phase to another, such as dissolving in an aqueous solution.

Protonation Reaction

Protonation reactions play a critical role in modifying the solubility and reactivity of compounds. These reactions involve adding a proton \((H^+)\) to a molecule, often from an acid.

For amines, protonation impacts solubility due to the formation of positively charged ions. Key attributes of protonation include:

• Making originally non-polar compounds polar.
• Increasing water solubility for compounds like amines.
• Facilitating separation from non-reactive hydrocarbons.

During the separation of benzene and aniline, adding \(HCl\) initiates a protonation reaction. Aniline is protonated, becoming anilinium chloride. This compound is now water-soluble, allowing it to be removed from benzene in a liquid-liquid extraction. This selective reactivity exemplifies the utility of protonation in organic chemistry separations.