In chemistry, specifically organic chemistry, any time a reaction is done, the product must be purified. Sometimes it is easy, sometimes it is hard. Regardless, it is always a part of the reaction.
There are myriad techniques to purify compounds. In the organic labs I teach, we go through the basic ones: crystallization, distillation, column chromatography etc...
Of all of the available techniques, my favorite is sublimation. Sublimation rocks AND rolls. Sublimation describes the change of a solid to a gas. If the gas is cooled, the solid can reform. [Bonus points if you know the name of this process. It's not condensation].
Purification by sublimation involves heating a solid in a flask that has a cold finger above the solid. This can be done under vacuum or at room pressure.
Recently I had my organic students synthesize ferrocene. This reaction involves the deprotonation of cyclopentadiene with potassium hydroxide. Most hydrocarbons would never be deprotonated by potassium hyroxide, but the cyclopentadiene is easily deprotonated because the product is aromatic. Upon reaction with iron II, it forms a nice orange sandwich compound.
This product is easily purified by crystallization from hexane, but sublimation is a lot more fun. If a product can be purified by sublimation, I will do it. Without question.
Here are some pictures I snapped of the purification by sublimation of student synthesized ferrocene.
Here's the crap before purification:
Here is the setup. The cold-finger is cooled with water. The hotplate is heated to "4." Whatever that means.
After about an hour, the ferrocene deposits on the side of the flask. I usually put a Al foil tent around it to contain the heat and keep the whole flask warm. That way more of the product ends up on the cold finger.
Here's the cold finger with some purified ferrocene upon it.
This is the crap left behind.
And this is the final product.
I love sublimation!!!!!!
UPDATE: Here are some products I have purified by sublimation.