Question

3. What is the purpose of evaporating the mixture then condensing it back to the original mixture (Refluxing)? Explain.

Answer 1

3. A chemical reactions are mainly of two types, first is solution phase chemical synthesis and second type is solid phase chemical synthesis. In solution phase type all the reactants used to convert the desired products are in liquid state or have a partial to complete solubility in the solvent used for the reaction to take place. In solid phase type the all the reactants are in sold state or may be reaction take place on the solid resin.  

In solution phase chemical reactions, we need to use a single or the mixture of the solvents (methanol, ethanol, THF, DMF, dichloromethane, CHCl3, 1,4-dioxane, ether, DMSO and other solvents) to dissolve all the reactants used for the chemical reaction. These solvent have low to high boiling point range.  The product formation process is either at room temperature or at the reflux temperature that means heating the reaction mixture at the boiling point of the solvent used for the reaction purpose.

The process of the conversion of the reactants to product in presence of the solvent, the heating of the reaction mixture is required for the few hours time to complete the reaction (formation of the product with maximum yield). It is also called the refluxing the reaction mixture. During heating the reaction mixture in the reaction assembly (comprises of the round bottom flask attached condenser with cold water circulation and fitted with guard tube) , the evaporation of the solvent vapours at their boiling point is occurred . These vapours were condensed back to the reaction assembly due to the condenser with circulated cold water.

This process of evaporation and condensation of the vapours from the reaction mixture will be continue in order to complete the product formation without any loss of the solvent used in the reaction mixture. It may take long hours time for the completion of the reaction. Once the reaction is completed and confirmed by TLC or analytical methods like HPLC/GC/MS, the solvent used can be recovered back by evaporation or distillation process and the product formed shall be obtained by work-up of reaction followed by the purification methods.