[dudeman]

Typically when you read literature you will find that almost every time that a free base amine is purified they distil it under vacuum. I know that it's better to distil under vacuum because it lowers the boiling point. This prevents decomposition of the substance due to high temperature but is this really needed? What are the typical repercussions of distilling a free base amine without applying a vacuum?

[fledarmus]

It really depends on the boiling point of the compound you are trying to purify. In a fairly well equipped organic lab, it is usually most convenient to distill things that boil between about 70 and about 120C. Below 70, and it gets hard to control the temperature so that it doesn't just *Ignore me, I am impatient* everything through, above 120 you start having to insulate your head and column or deal with very large temperature gradients - the vapor cools so fast that you need a very high pot temperature or good insulation above the pot to get the vapor to go over. These really high pot temperatures are usually what burns up your product, especially if you are distilling under air instead of inert gas. So if your compound boils higher than about 120C, its easier to use a vacuum distillation.

You can get a good estimate for what the boiling point of your compound will be at different pressures from a temperature-pressure nomograph. A quite useful one is here:

http://www.sigmaaldrich.com/chemistry/solvents/learning-center/nomograph.html

[orgopete]

Amines can react with oxygen and carbon dioxide. If you distill them under vacuum, you will remove these possible reactions. If you have bottle of aniline that has been exposed to the air, it will turn dark. If you distill it, it will remove the impurities.