Methods of Purification of Organic Compounds
Purification of compounds is an important step in organic chemistry. Purification of organic compounds is much more difficult because these occur as complex mixtures in nature. Organic compounds made in the laboratory are also impure because several side-products are formed during the reaction involving organic compounds. Therefore, it is necessary to purify organic compounds before an attempt can be made to characterize them, i.e. to know their chemical composition, molecular or structural formula, etc.
Characterization of a compound is done is several steps. A pure compound is subjected to qualitative analysis to know the different elements present in it. Later quantitative analysis is done to know the exact percentage of each element present in the compound. This enables us to calculate the empirical formula. Molecular formula can be calculated by knowing the molecular mass of the compound. Structure of the organic compound can be known by various physical and chemical methods.
Purification is a simple technique that is most widely used for the purification of organic compounds. This method is particularly useful when the solubility of impurities is quite different from the compound. In this method, the impure substance is dissolved in water or some other suitable organic solvent such as alcohol, petrol, chloroform, etc. The solution is filtered to remove any suspended impurities. The filtrate is concentrated to make a nearly saturated solution at or near the boiling point of the solvent. Solutions are concentrated by heating over a water bath so that the vapours of the solvent may not catch fire. Organic compounds have more solubility at a higher temperature and a lower solubility at a lower temperature.
Thus when a hot saturated solution of an organic compound is cooled, its crystals begin to separate out. The crystals are removed by filtration and the impurities are passed on to the filtrate.