Question

Which of the following reagents can be used to separate a mixture of aniline and phenol here? (1) \(\mathrm{NaHCO}_{3}\) (2) Bromine \(/ \mathrm{H}_{2} \mathrm{O}\) (3) \(\mathrm{NaOH}\) (4) \(\mathrm{HCl}\) (a) 1 and 3 (b) 2 and 4 (c) 3 and 4 (d) 1,3 and 4

Short answer

(c) 3 and 4

Step-by-step solution

Understanding the Problem

We want to separate a mixture of aniline and phenol using chemical reagents. The reagents will selectively react with one component but not the other, allowing for separation.

Evaluating the Reagents

Evaluate how each reagent interacts with aniline and phenol: 1. **NaHCO₃**: Phenol, being acidic, can react with sodium bicarbonate, forming a soluble phenoxide ion. Aniline, a weak base, does not react with NaHCO₃. 2. **Bromine / H₂O**: This can react with phenol through electrophilic aromatic substitution, but does not help in separating while aniline is present. 3. **NaOH**: Can deprotonate phenol to form a soluble phenoxide. Aniline does not react as strongly with NaOH. 4. **HCl**: Aniline will react with HCl to form aniline hydrochloride, a soluble salt, whereas phenol remains unaffected in the absence of a basic medium.

Choosing the Correct Options

To separate the mixture, a combination of reagents that selectively reacts with one compound in the mixture should be used. Using NaOH, phenol can be converted into sodium phenoxide, and using HCl, aniline can be converted to aniline hydrochloride. These methods provide a means of separation.

Selecting the Best Answer

The correct combination of reagents for separating aniline and phenol is NaOH and HCl, which corresponds to option **(c) 3 and 4**.

Key concepts

Aniline Separation

Aniline and phenol are two organic compounds that often need to be separated due to their different chemical properties. These compounds can be separated based on their reaction with specific chemical reagents.
Aniline is a weak base and can react with acids to form soluble salts. By using hydrochloric acid (HCl), aniline reacts to form aniline hydrochloride, which is soluble in water. This reaction is specific because phenol, unlike aniline, does not react with HCl in a basic medium. Instead, phenol remains relatively unreacted by acid. Therefore, in a mixture, aniline can be separated from phenol by selectively converting aniline into a water-soluble salt with HCl.

• Aniline reaction: Aniline + HCl → Aniline hydrochloride (soluble in water)

By using this principle of forming a soluble salt, we can effectively isolate aniline from a mixture where phenol is present.

Phenol Reaction

Phenol, being a weak acid, can undergo reactions that are different from aniline. One of the common reactions involves converting phenol into a phenoxide ion using a strong base like sodium hydroxide (NaOH).
When NaOH is added to a phenol solution, it deprotonates the phenol to form a sodium phenoxide ion, which is soluble in water. This reaction allows phenol to be separated from other substances that do not react with NaOH, such as aniline.

• Phenol reaction: Phenol + NaOH → Sodium phenoxide (soluble in water)

Through this method, phenol physical state changes as it forms phenoxide, making it distinct from other components that remain unchanged, allowing for effective separation techniques in organic chemistry.

Chemical Reagents

Chemical reagents are essential for inducing or facilitating specific reactions in organic compounds such as aniline and phenol. Their function is critical when separating compounds based on their unique chemical properties.
Different reagents are chosen based on their ability to selectively react with specific components in a mixture. For example:

• Sodium Bicarbonate (NaHCO₃): Reacts with acidic components like phenol but not basic components like aniline.
• Bromine: Can react with phenol but would not help in the separation from aniline. It instead leads to electrophilic aromatic substitution.
• Sodium Hydroxide (NaOH): Deprotonates phenol to form soluble phenoxide, allowing its separation from non-acidic substances like aniline.
• Hydrochloric Acid (HCl): Reacts with aniline to form a water-soluble salt without affecting phenol in the same medium.

In selecting appropriate reagents, understanding the chemical behavior of each compound in the mixture is key to achieving successful separation and purification. By choosing the right reagent, you can target specific chemical reactions needed for effective separation.