December 01, 2021, 07:27:59 PM
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Topic: Advice on purification of volatile compounds  (Read 598 times)

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Offline gespy

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Advice on purification of volatile compounds
« on: September 20, 2021, 05:33:36 AM »
Hi, I need a piece of advice. I'm not a newbie in chemistry, but I usually work with relatively large molecules.

In my current project, I'm working with some compounds, which are volatile enough to be at least partially gone during rotary evaporation. Therefore, I have very low isolated yields after initial treatment and subsequent column chromatography.

What are some purification techniques I can use to avoid this?

I'm thinking of trying distillation, but I have relatively small amounts (running reactions on 0.5 to 1 mmol scale for now)...

Thank you in advance.

Online Babcock_Hall

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Re: Advice on purification of volatile compounds
« Reply #1 on: September 20, 2021, 09:59:26 AM »
There is short path distillation glassware, but I am not sure whether or not it would be satisfactory for your application.

Offline MOTOBALL

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Re: Advice on purification of volatile compounds
« Reply #2 on: September 20, 2021, 03:23:09 PM »
What are the physical states of your reaction products at STP?

Regards,

Motoball

Offline rolnor

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Re: Advice on purification of volatile compounds
« Reply #3 on: September 20, 2021, 04:46:14 PM »
There is really no way but distillation. There is micro-equipment but you will get loss of yield in this small scale.

Offline gespy

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Re: Advice on purification of volatile compounds
« Reply #4 on: September 21, 2021, 03:37:33 AM »
What are the physical states of your reaction products at STP?

Regards,

Motoball

Mostly clear non-viscous liquids, I'm working with different substituted aromatics and some simple benzene derivatives are quite volatile. Actually much more than I expected them to be from my general chemical experience...

Offline gespy

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Re: Advice on purification of volatile compounds
« Reply #5 on: September 21, 2021, 03:38:34 AM »
There is really no way but distillation. There is micro-equipment but you will get loss of yield in this small scale.

Yeah, this is my thought at the moment too, just posted here in case I was missing smth I'm not familiar with :)

Thanks

Offline rolnor

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Re: Advice on purification of volatile compounds
« Reply #6 on: September 21, 2021, 06:13:18 AM »
You can use low-boiling solvents like pentane and ether for chromatography, this way you can have aspirator vacuum and ice-cold waterbath when evaporating.

Offline wildfyr

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Re: Advice on purification of volatile compounds
« Reply #7 on: September 22, 2021, 06:06:57 PM »
On the small scale yields tend to be poor :( just a fact of life. Stuff sticks to the walls, evaporates a bit, etc.

What's the reason you can't go up 2-3x? Money? Poor yields cost money too if you have to rerun mulitple times... with your time and solvents included its more expensive!

Offline gespy

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Re: Advice on purification of volatile compounds
« Reply #8 on: September 23, 2021, 03:38:36 AM »
On the small scale yields tend to be poor :( just a fact of life. Stuff sticks to the walls, evaporates a bit, etc.

What's the reason you can't go up 2-3x? Money? Poor yields cost money too if you have to rerun mulitple times... with your time and solvents included its more expensive!

Right now I'm doing reaction scope for the new procedure, so I'm doing a lot of the same reaction on different substrates. For some scale is not a problem, for some I don't have that much of a starting compound. Also, I don't need a lot of each final product, just enough for characterization and good yields (hopefully) for the publication :)
Normally 1 mmol is perfect balance for such stuff.

Online Babcock_Hall

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Re: Advice on purification of volatile compounds
« Reply #9 on: September 23, 2021, 09:49:50 AM »
https://www.amazon.com/Precision-Vacuum-Jacketed-Distillation-Apparatus/dp/B016X1W3TK

I have seen short path distillation glassware both with and without a jacket.

Offline gespy

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Re: Advice on purification of volatile compounds
« Reply #10 on: September 23, 2021, 09:54:58 AM »
https://www.amazon.com/Precision-Vacuum-Jacketed-Distillation-Apparatus/dp/B016X1W3TK

I have seen short path distillation glassware both with and without a jacket.

Thanks. Haven't used this one... Will take a look around if we have smth like this to try :)

Offline rolnor

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Re: Advice on purification of volatile compounds
« Reply #11 on: September 23, 2021, 01:56:08 PM »
Yes, thats a usefull device! Impressive that amazon has glassware….

Online Babcock_Hall

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Re: Advice on purification of volatile compounds
« Reply #12 on: September 23, 2021, 03:47:30 PM »
You would not believe what I have found on eBay, also.

Offline rolnor

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Re: Advice on purification of volatile compounds
« Reply #13 on: September 23, 2021, 04:32:31 PM »
I have bought som glass from ebay, but I must warn for the chinese equipment, they can not make proper cylindrical glass-joints, this has resulted in several cracks in my flasks I use for evaporation, very dangerous!
In my workplace in Stockholm we had very tiny distillation apparatus where you could collect fractions in a set of 0.5ml tubes, I dont know who made these, I can not find anyone in a web-search.

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