soma
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purifying secondary amine
We've got about 1/4 of a 1L bottle of dipropylamine that's been sitting for several years. I was wondering what impurities might be in there now and
how to purify it.
Help appreciated.
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Hexavalent
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How is it stored?
If in an amber glass bottle in appropriate conditions, e.g. away from any acids, oxidizers etc., I can't see too many impurities building
up...although a quick distillation to be sure wouldn't be a bad thing (just be sure to do it in a fume hood!).
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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soma
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It's in amber glass. I wondered if the CO2 in the air might cause a problem. I know that CO2 in the air can cause some problems with NaOH after
awhile.
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Dr.Bob
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Secondary amines will get impure by several routes over time. They absorb CO2 for form the carbonate salts, which often create solids on the bottle
lid. They also can air oxidize to form N-oxides, which render them useless in normal amine chemistry like forming amides. And they can react with
water and air to form more complex dimers and oxidation products, which is typically more of a problem with benzyl amines.
The simplest way to purify an amine like dipropylamine would be to distill it, even a simple distillation will provide much purer amine, although you
will need to do it under vacuum or under nitrogen (or some other inert atmosphere) for the best results, as any air or CO2 will react even faster when
it is warm. But typically a simple distillation will remove most of the byproducts, as almost all of them are higher molecular weight and BP than
the amine. If you really want it pure, distilling from a drying agent like CaH2, KOH, or other basic drying agent will help even more. (Please do
make sure that it is compatible with the amine used). Just watch the BP and when it starts rising above where it was steady, stop collecting.
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