Question

3. Why should reflux of the microscale reaction mixture be gentle, with the con- densation ring remaining close to the surface of the liquid in the test tube?

Answer 1

As many chemical reactions are not spontaneous at standard temperature and pressure, it is necessary to provide some energy to proceed. A good way to do this is to raise the temperature of the reaction vessel in order to provide thermal energy. But, choosing a specific temperature is not simple without specialized equipment, so sometimes it is easier to design a solvent system that boils at the desired temperature, and then to perform the experiment at the boiling point. This is called reflux. In order to prevent the loss of solvent, a condenser is attached to the reaction vessel to cool and collect any evaporated solvent and return it to the vessel.

Now, microscale reactions use extremely small amounts of solvents and reagents. In a reflux reaction, some solvent leaves the reaction vessel as it boils and is condensed above. The higher the condensation ring , the less solvent there is in the reaction vessel. Since small quantities of solvent are used, this can cause your reaction to dry up or burn.