Chemgineer
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Soxhlet extraction
I've been using a soxhlet extractor recently, i'm using 95% ethanol and have been extracting lemon from dried peel.
I typically keep the ethanol in the flask and replace the spent lemon peel multiple times. I notice my final solution is very dark and red/brown in
colour.
Is it likely I am degrading/burning the lemon extract or is it just dark due to the concentration?
Is it normally better to just do a single extraction and then replace with fresh solvent for the next run or is my approach acceptable?
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Texium
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What are you trying to get out of it? If you’re after limonene or other volatiles, then Soxhlet extraction is just the wrong approach, and you
should use steam distillation instead.
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Rainwater
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| Quote: | | Is it likely I am degrading/burning the lemon extract or is it just dark due to the concentration? |
It could be sugar, but deffenetly side reactions
Small amounts of acid can react with ethanol.
If you leave it you will end up with sweet-smelling tar and some very low bp compounds.
Sugars are a pain to remove.
You may want to pick a solvent that your target and sugar differ greatly in solubility.
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Chemgineer
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Quote: Originally posted by Rainwater  | | Quote: | | Is it likely I am degrading/burning the lemon extract or is it just dark due to the concentration? |
It could be sugar, but deffenetly side reactions
Small amounts of acid can react with ethanol.
If you leave it you will end up with sweet-smelling tar and some very low bp compounds.
Sugars are a pain to remove.
You may want to pick a solvent that your target and sugar differ greatly in solubility.
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Thanks, that's useful information, whilst recovering limonene would be good, I am more trying to teach myself how to do extractions and when and where
to use different approaches.
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Tsjerk
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Peels are full of all kinds of organics, and many decompose/react upon prolonged heating
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Chemgineer
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| Quote: Originally posted by Texium | | What are you trying to get out of it? If you’re after limonene or other volatiles, then Soxhlet extraction is just the wrong approach, and you
should use steam distillation instead. |
The last steam distillation I tried ended up with a product that seemed to be a suspension of oil in water and wouldn't easily separate into layers.
[Edited on 13-11-2022 by Chemgineer]
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Tsjerk
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That often happens after steam distillation, you can extract with a solvent with a different bp and distill it again.
[Edited on 13-11-2022 by Tsjerk]
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Rainwater
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Recommended reading
Techniques for extraction and isolation of natural products: a comprehensive review
Attachment: Techniques for extraction and isolation of natural products a comprehensive review.pdf (1.2MB)
This file has been downloaded 231 times
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Sulaiman
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Soxhlet vs. excess solvent?
For an amateur like me,
rather than getting a soxhlet kit,
why not just use a large excess of solvent,
then distill off most of it (for later re-use)
then filter out any solids
leaving a solution similar to what a soxhlet would have produced?
CAUTION : Hobby Chemist, not Professional or even Amateur
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Bedlasky
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Methyl ethyl ketone from denaturated EtOH + acids from lemon --> aldol condensation products. Ethanolic solutions of KOH are usually yellow because
of this.
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Texium
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| Quote: Originally posted by Sulaiman | For an amateur like me,
rather than getting a soxhlet kit,
why not just use a large excess of solvent,
then distill off most of it (for later re-use)
then filter out any solids
leaving a solution similar to what a soxhlet would have produced? |
Multiple extractions with smaller amounts
of solvent is much more efficient than a single extraction with a large amount of solvent. Also, if I was extracting volatiles into the solvent, I
wouldn't trust it for reuse, even if it was distilled, unless I used a very efficient column, but at that point, it's probably not even worth it.
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