Purification and characterization of organic compounds

General Organic Compound Purification Methods

Depending on the nature of the chemical and the impurities present, many techniques of purification of organic compounds are used. The following purifying procedures are often used:

• Sublimation: When some compounds are heated, they directly convert to a vapour state without transitioning to a liquid state, and when these vapors are cooled, they directly convert to a solid-state.
• Crystallization: This process is effective for the solid-state purification of organic molecules. The difference in the solubilities of the chemical and the contaminants in a suitable solvent is the basis for this approach.
• Simple distillation: It is a method for separating non-volatile contaminants from volatile liquids. This approach is also employed when the boiling points of two liquids differ by a substantial amount (30 K-50 K).
• Fractional Distillation: This method is excellent for separation when the boiling temperatures of two volatile liquids differ by only a few degrees (10 K – 15 K).
• Distillation at Reduced Pressure: This process is excellent for purifying liquids with extremely high boiling points as well as those that disintegrate at or below their boiling points.
• Steam Distillation: This process is effective for compounds that are insoluble in water and volatile in steam.
• Differential Extraction: It is the technique of extracting organic compounds contained in an aqueous solution by shaking them with an organic solvent that is more soluble than water.
• Chromatography: This process is effective for separating mixtures into their constituents, purifying substances, and testing compound quality.

Organic Compounds Qualitative Analysis

Organic compounds mostly contain components such as carbon and hydrogen. In addition, they contain components such as N, S, P, and X. These elements are detected using a Lassaigne test.

Organic compound quantitative analysis and molecular weight

• Leibig’s technique is used to calculate the percentage amount or proportion of carbon and hydrogen.
• To calculate the percentage proportion of nitrogen, the Dumas and Kjeldahl techniques are utilized.
• The Carius technique is used to calculate the percentages of X (halogen), S, and P in organic compounds.
• In general, the percentage of oxygen contained in an organic complex is calculated by subtracting the total percentage of other elements from 100.

FAQs

Question. What is the distinction between distillation, low-pressure distillation, and steam distillation?

Answer:

• Distillation is effective when dealing with volatile liquids that are combined with a non-volatile contaminant.
• Distillation at decreased (low) pressure is typically used to purify liquids with extremely high boiling points or that may dissolve at or below their boiling points.
• Steam distillation separates steam volatile liquids from contaminants that are immiscible in water.

Q. What is the difference between the principles of estimating nitrogen in an organic molecule using the Dumas technique and (ii) the Kjeldahl method?

Answer: Dumas Method: an organic compound is forcefully heated in an environment of CO₂ with an excess of CuO until free nitrogen, carbon dioxide, and water are produced.

Kjeldahl’s Method: A known mass of an organic substance is heated vigorously with a conc. H₂SO₄, a trace of potassium sulfate, and a trace of mercury (a catalyst). The nitrogen in the molecule is converted into ammonium sulfate as a result of the reaction.