Simple distillation

The procedure for doing a simple distillation is described in Box 15.2 and you should note the following points:

• Do not distil to dryness, i.e. no liquid remaining in the distillation flask, since this causes overheating and charring (decomposition) of the residue. Always leave 1 or 2 mL of liquid in the distillation flask.
• Initially, some liquid may distil while the temperature rises rapidly. This is termed 'forerun', for example often a small amount of solvent from an extraction process: collect and then, when the temperature stabilizes, collect the desired compound in a clean receiving vessel.
• Towards the end of the distillation, the temperature may begin to rise again: this will be the higher boiling impurity. Stop heating, quickly remove the receiving flask containing your pure compound and collect these last few drops, termed 'tailings', in a fresh receiving vessel.