bob800
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Carotene extraction help
Today I tried to extract carotene from dried carrots, following the procedure from the Book of Projects for the Amateur Scientist (which BTW is on the
forum library and is full of fascinating projects!):
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To extract carotene you grind five grams of dried carrot root to
dust in a mortar and then add 50 milliliters of a mixture of equal
parts of wood alcohol and petroleum ether. Shake the mixture thor-
oughly, add five milliliters of water and pour into a separatory fun-
nel. The carotenes, plus xanthophyll esters, are concentrated in the
petroleum ether layer that forms at the top. Separate this layer and
concentrate it by evaporating some of the fluid, leaving 20 milli-
liters.
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I experienced several problems during the extraction (keep in mind I've never done this before). After adding the 5mL of water, I poured the mixture
into the sep. funnel as per the procedure. However, it was impossible to avoid decanting only the solution and not the carrot, so my funnel became
clogged. Anyway, I decided to pour out the mixture and vacuum filter it, and then put the solution back into the sep funnel. After standing for
several minutes, no sign of separation was observed. I tried shaking it and venting, but still no separation occurred after standing.
Is the filtering step always required (it was not stated in the procedure), or was I doing something wrong? I did substitute denatured alcohol (free
of additives) for the ethyl alcohol, but I can't see why that would cause a problem (carotene is slightly soluble in both methyl and ethyl alcohol).
Also, there is a small hole drilled towards the bottom of the ground glass joint on my funnel. When I shook the funnel to mix its contents, the
solution would dripped out this hole (even after adding grease). Is this hole normal? (I can take a pic if necessary).
Any advice would be greatly appreciated. Thanks!
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Paddywhacker
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With science you are expected to use common sense more than following procedures blindly. If you were having trouble separating your extract from the
solids then of course you should filter, but I would have thought filtering through a cotton wool plug would have been faster and easier than vacuum
filtering.
The small hole was probably a vent to be used with a longer stopper than the one you are using now. This long stopper would have a groove running
from the base of the stopper up to where the hole is on the funnel. By rotating the stopper to align with the hole you could vent the funnel, and
then rotate back to block the hole. If you don't have a stopper long enough then seal the hole, maybe with epoxy.
The next thing to do, when you have an extract, is to purify by chromatography. That is a lot of fun, as you can see the various compounds
separating, and maybe collect them all separately and not just the carotene.
Edit: No separation ... either not enough petroleum (it might have evaporated) or not enough water.
[Edited on 15-7-2011 by Paddywhacker]
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fledarmus
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Quote: Originally posted by bob800  |
| Quote: |
To extract carotene you grind five grams of dried carrot root to
dust in a mortar and then add 50 milliliters of a mixture of equal
parts of wood alcohol and petroleum ether. |
I did substitute denatured alcohol (free of additives) for the ethyl alcohol, but I can't see why that would cause a problem (carotene is slightly
soluble in both methyl and ethyl alcohol).
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(quotes snipped to highlight possible issues)
It's possible the alcohols are your issue, especially if the denatured alcohol is denatured with something besides methanol. Wood alcohol is methanol,
and petroleum ether is less soluble in methanol than ethanol. It is possible that with enough ethanol, or too little petroleum ether, or the presence
of less polar denaturing agents such as acetone or MEK, you would end up with a homogeneous mixture.
And as Paddywhacker noted, the petroleum ether is very volatile - you may have simply stripped it off with your vacuum filtration. Adding more pet
ether might give you a separate layer.
Finally, you can try adding a little salt (NaCl) to the mixture. This increases the polarity of the water layer slightly, and may help to get the
layers separated in your first pass. You don't want enough salt to saturate the water, or you may force other impurities back into the organic phase.
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bob800
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Thank you for your responses!
I think you're right about the ether evaporating. The bottom of my reaction beaker was FREEZING, probably due to rapid evaporation. Next time I'll try
it with a corked flask (or would that build up too much pressure?), and the cotton idea for filtering.
My denatured alcohol is completely clear and denatured with only methanol, so unless the ether/ethanol solubility difference is the problem, I don't
think the alcohol is the culprit.
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