What is Purification of Organic Compounds: Methods of Purification, Impurities, Checking Purity After Purification

Students in chemical labs often don't necessarily consider it important to purify organic compounds. Here are a few reasons which are enough to change their mind:

• Obtaining accurate results is only possible if compounds are free of any unwanted particles. Calculating melting points, resistivity, boiling points etc. require pure compounds to fiigure out exact values.
• Presence of impurities can reduce the quality of the compound and make it less reliable for experimental purposes.
• Industrial safety standards consider impure compounds to be legally unfit for consumer purposes due to being toxic.
• Buyers aspire for pure organic compounds which are healthy enough to be used in daily lives.

There are some basic rules and regulations which the final product must fulfil in order to be considered fully pure and fit for use. These eligibility standards are important to be met so that the product can be considered safe for commercial use. Some of these standards are mentioned below:

Melting Point (for solids): Pure compounds will have a specific melting point.

Boiling Point (for liquids): Pure compounds will have a constant boiling point.

Chromatography: If there are more than 1 spots shown by techniques like TLC, it indicates impurity, Pure compounds will only have a single spot.

Spectroscopy: IR, NMR, etc. are some of the techniques used for advance purity detection.

There are several ways to purify organic compounds, depending on their properties (like whether theyre solid, liquid, or how they dissolve). Let's go through the key methods for JEE Main.

1. Sublimation

In this technique, we convert solid substances directly into gas without it even reaching the liquid stage. This is done by heating the substance at a suitable temperature to remove useless impurities, which add up randomly to the compound.

Examples: Camphor, Naphthalene, etc.

2. Crystallization

This is the most common technique used to purify compounds, specifically solids. In this technique, we dissolve the solid in a hot solvent and then start cooling it slowly. Due to this, the impure particles form crystals, which are then filtered to separate it from the pure organic compound.

3. Distillation

This technique involves purifying liquid compounds according to their boiling points. We heat the solution to evaporate the liquid so that impurities can be left behind. It's further types are:

• Simple Distillation: For liquids with very different boiling points.
• Fractional Distillation: For liquids with close boiling points.
• Vacuum Distillation: For compounds with high boiling points.
• Steam Distillation: For substances which are sensitive to temperature.

4. Differential Extraction

This is a method used to separate organic compounds from aqueous solutions. Here, we use an organic solvent that doesn't mix with water. The goal is to dissolve organic compound in the solvent, leaving impurities in the water. This method is suitable when the compound dissolves better in the organic solvent as compared to water.

5. Chromatography

Chromatography is an advanced technique used to separate, analyze, and purify compounds based on their movement through a medium (can be stationary or mobile). There are different types of chromatography, which are mentioned as follows:

• Paper Chromatography
• Thin Layer Chromatography (TLC)
• Column Chromatography
• Gas Chromatography (GC)
• High Performance liquid chromatography (HPLC)