Problem 20 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

Which of the following cannot be separated by steam distillation? (a) Nitrobenzene (b) Essential oil (c) Aniline (d) Glycerol

Step-by-Step Solution

Answer

Glycerol cannot be separated by steam distillation.

Step 1: Understanding Steam Distillation

Steam distillation is a separation process used when the compound has a high boiling point and can decompose at its boiling point. It is used for temperature-sensitive materials such as aromatic substances.

Step 2: Analyzing the Options

Consider each option: (a) Nitrobenzene, (b) Essential oils, (c) Aniline, (d) Glycerol. Steam distillation is typically used for separating volatile compounds like essential oils from plant material.

Step 3: Evaluating Nitrobenzene

Nitrobenzene has a boiling point of 210°C and can be separated by steam distillation as it is volatile enough to be vaporized by steam.

Step 4: Evaluating Essential Oils

Essential oils are commonly separated using steam distillation due to their volatile nature and sensitivity to high temperatures.

Step 5: Evaluating Aniline

Aniline has a boiling point of 184°C and is also volatile enough to be separated by steam distillation.

Step 6: Evaluating Glycerol

Glycerol has a high boiling point of about 290°C and is non-volatile, making it unsuitable for separation by steam distillation.

Key Concepts

Nitrobenzene

Nitrobenzene is an organic compound with the chemical formula \(C_6H_5NO_2\). It is known for its pale yellow appearance and a distinct almond-like odor. One of its key properties is a high boiling point of 210°C.
This makes it volatile enough to be separated from mixtures via steam distillation, a valuable property for such aromatic compounds.

• Boiling Point: 210°C
• Appearance: Pale yellow liquid
• Odor: Almond-like

Nitrobenzene is primarily used in the manufacture of aniline, which is crucial for producing dyes. Its volatility under steam distillation conditions allows for efficient separation without decomposition.

Essential Oils

Essential oils are concentrated plant extracts that retain the natural flavor and scent of their source. They are derived from flowers, roots, seeds, or leaves, and hold significant therapeutic and aromatic value. These oils are highly valued in aromatherapy, perfumery, and natural medicine.

• Source: Plant materials
• Method of Extraction: Steam distillation
• Uses: Aromatherapy, perfumes, health remedies

Steam distillation is the most common method for extracting essential oils. This process is preferred because it allows for the separation of the oil without high temperatures that could degrade the quality and efficacy of the compounds.

Aniline

Aniline is an amine compound represented by the formula \(C_6H_5NH_2\). Known for being slightly oily and colorless, it turns brown upon exposure to air and light due to oxidation.
Aniline's relevance is primarily in the industrial sector, where it is a foundational component in the manufacture of dyes, resins, and rubber processing chemicals.

• Boiling Point: 184°C
• Appearance: Colorless liquid (turns brown on exposure)
• Industrial Uses: Dyes, resins, polymers

This compound's volatility allows it to be separated from mixtures via steam distillation. The method ensures protection from thermal decomposition, preserving the integrity of the compound during extraction.

Glycerol

Glycerol, also known as glycerine, is a simple polyol compound. It is renowned for its sweet taste, hygroscopic nature, and its role as a moisture-retaining agent in various products. Commonly used in food, cosmetics, and pharmaceuticals, glycerol's versatility is extraordinary.

• Boiling Point: ~290°C
• Properties: Sweet, colorless, hygroscopic
• Applications: Food industry, skincare, medicine

Unlike the other compounds discussed, glycerol's high boiling point and non-volatile nature make it incompatible with steam distillation. Instead, glycerol is often separated using other methods like vacuum distillation, which caters to its thermal stability and non-volatile characteristics.