ORGANIC cHEMISTRY - I

Experiment 3

Aim of the Experiment

Purification of organic compounds by crystallization by using methanol as the solvent

Principle

• Crystals are the purest form of the substances having definite geometrical shapes.

• The process by which impure compound is converted into its crystals is called as crystallisation .

• It is based on the difference in the solubility of the compound and the impurities in a suitable solvent.

• The impure compound is dissolved in the suitable solvent in which it is sparingly soluble at room temperature but appreciably soluble at higher temperature.

• The solution is concentrated to get a nearly a saturated solution.

• When this saturated solution is cooled, crystals of pure substances will separate out which are removed by the filtration.

• The filtrate contains the impurities along with small quantity of the organic compound. If the compound is highly soluble in one solvent and too little soluble in another solvent , then crystallisation can be carried out in a mixture of these solvents taken in the suitable ratio

Materials required

Organic Compound, Methanol

Procedure

• The impure substance is finely powdered and then heated in the conical flask with a small quantity of the methanol which is just sufficient to dissolve whole of the substance on boiling .

• The hot solution obtained above is then filtered immediately either through filter paper or through hot water funnel to avoid crystallisation during filtration.

• The beaker containing the solution is them allowed to cool undisturbed when after sometime crystals begin to separate out.

• If crystals do not appear even after long time, then it may be necessary to scratch the sides of the dish with the glass rod.

• The crystals are finally dried either in air or by placing them in steam oven.