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benzeentje
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Extraction of caffeine with diethyl ether
Hi all,
I'm going to try a basic caffeine extraction from coffee. I'm going to take 100ml of strong coffee (wich I already boiled down to 2/3 of its original
volume) and extract 3 times with 10ml of diethyl ether. Then i'm going to boil off the ether in an erlenmeyer on a hotplate untill crystals start to
form.
Does anyone see any flaws in my procedure or have recommendations?
Also, i noticed that the solubility of caffeine in water at room temperature is +-2g/l. The concentration of caffeine in coffee is around 100mg/100mL.
That is 1g/l. So if I simply boil down coffee untill it's 1/10 of its original volume, wouldn't the caffeine precipate out?
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Bot0nist
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Try to add base to the aquas extract before extracting into the ether. Sodium carbonate/bicarbonate will work, as will weak NaOH solution. See peach's
write up in prepublication for some pointers. Good luck, and I look forward to seeing the results.
http://www.sciencemadness.org/talk/viewthread.php?tid=14139
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benzeentje
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I have NaOH 0.1M. Is this just done to raise the pH? and do i have to neutralize it later on with HCl to see crystals?
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Dr.Bob
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You might get some coffee from water by concentrating, but remember there are many other things in coffee which will also ppt out of water at some
point.
Ether might work OK, but it is highly flammable, and boils at about 40 C, so you should not heat it directly with a hotplate. Use hot water or just
blow some air over it to evaporate it.
The faster you evaporate, the poorer the crystals obtained.
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benzeentje
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Quote: Originally posted by Dr.Bob  | You might get some coffee from water by concentrating, but remember there are many other things in coffee which will also ppt out of water at some
point.
Ether might work OK, but it is highly flammable, and boils at about 40 C, so you should not heat it directly with a hotplate. Use hot water or just
blow some air over it to evaporate it.
The faster you evaporate, the poorer the crystals obtained.
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I don't really understand. A hotplate doesn't use a flame, so i'm not really concerned about flammable vapours. The idea is to use a large beaker as
warm water bath, try too keep it +-50°C and put my erlenmeyer in this. the beaker is then heated by a hotplate.
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Bot0nist
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A hotplate will easily flash ether on contact. Use a hot water bath.
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Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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marko
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Hmm, autoignition of ether is 160C according to google. I know it's very volatile, but I didn't think it was quite that low!
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Adas
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| Quote: Originally posted by marko | | Hmm, autoignition of ether is 160C according to google. I know it's very volatile, but I didn't think it was quite that low! |
This is not true, I tried putting red hot copper wire into ether and it didn't ignite.
Rest In Pieces!
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marko
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I presume that is for the vapour, at proper air/ether mixture, not liquid.
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Nicodem
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| Quote: Originally posted by benzeentje |
I'm going to try a basic caffeine extraction from coffee. I'm going to take 100ml of strong coffee (wich I already boiled down to 2/3 of its original
volume) and extract 3 times with 10ml of diethyl ether. Then i'm going to boil off the ether in an erlenmeyer on a hotplate untill crystals start to
form.
Does anyone see any flaws in my procedure or have recommendations? |
It seems to me you don't have much experience with experimental work, so I would suggest you to avoid reinventing the wheel and doing it the wrong way
also. Use one of the verified caffeine extraction procedures or else you will just cause yourself unneeded frustrations. Also, coffee is the worst you
can take as a caffeine source. It has a relatively low content of caffeine and contains all kind of other crap. Just buy the cheapest green tea you
can get and use a standard procedure.
Besides, how much do you think the partition coefficient of caffeine for diethyl ether / water is?
| Quote: | | Also, i noticed that the solubility of caffeine in water at room temperature is +-2g/l. The concentration of caffeine in coffee is around 100mg/100mL.
That is 1g/l. So if I simply boil down coffee untill it's 1/10 of its original volume, wouldn't the caffeine precipate out? |
Compounds rarely just precipitate out of complex mixtures. The solubility in water is a property specific for solutions in water. You don't have water
there, you have coffee!
| Quote: | | I have NaOH 0.1M. Is this just done to raise the pH? and do i have to neutralize it later on with HCl to see crystals? |
You don't need to add any base. The pH has little influence on the partition of caffeine, except at extreme values. The pKa of caffeine is about 0.5,
so its protonation in water is negligible even in moderately acidic media. The reason why some people suggest to basify the solution is just out of
thoughtless routine (as for some reason they believe that all alkaloids are alkaline).
PS: Please open referenceless threads only in the Beginnings section.
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Nicodem
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Thread Moved
21-3-2012 at 14:07 |
benzeentje
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I have no idea what the Kd is for ether/coffee, but i was told i could use ether as a (worser) substitute for chloroform or DCM as solvent. Since i
thought it would be wise to avoid chlorinated compounds in my house without the proper equipment, i looked around and found other people use ether to
extract caffeine. Are you insinuating that ether wont work since caffeine solves better in water? If so, that would mean i need to find another
solvent...
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Nicodem
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I'm sure you can use diethyl ether if you have a continuous extractor.
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Number 9
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Caffeine is insoluble in ether or carbontetrachloride, BUT: it is slightly soluble in water. So, what do you think about the result?
However, it is soluble in chloroform and pyridine. My advise is to get rid off these solvents first before you waste your time.
If the extraction works, you get very low yields and end with a brownish mess with a few milligrams caffeine in it. To purify your caffeine, you have
to sublimate it at 90 degree celcius (e.a. cold finger method).
Much blablabla but did you do already efforts?
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arsphenamine
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If you read some of the original recipes for Coca Cola, Pepsi, et.al., you see that they dissolved caffeine in aqueous phosphoric acid.
Caffeine's pKb is 10.4 -- low pKa values refer to the protonated form (conjugate acid).
For organic extraction, you want to force it out of solution, into suspension with a weak base like Na2CO3, and extract with a small chloro-alkane
like methylene chloride or chloroform.
Alternatively, you allow the alkaline sediment to aggregate, filter it, and extract the solid residue with ethyl acetate.
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benzeentje
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Well, i tried my extraction today and met complete failure. My coffee and ether form a very viscous emulsion. I tried to settle it for over an hour,
and still I didn't see any change. Then i tried to add salt (to make the water layer more polar). When I added this, the salt just floated on top of
the emulsion, and started to sink very, very slowly. Then I tried to gently stir it, and again let it settle for an hour.
After an hour, I clearly saw 2 fases, and drained the top one. However, this was only 5 mL. I added 25mL of ether to begin with, so this was very
little. When trying to heat this 5mL, most of the liquid boiled off, but there was still 1mL or so that didnt boil at 60°C. When I heated the mixture
at +-100°C, the rest boiled off as well. There was no residue.
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Bot0nist
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Caffeine may begin to sublimate at above 100°C, IIRC.
[Edited on 24-3-2012 by Bot0nist]
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Number 9
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Sublimation point of caffeine is exactly @ 90 degree celcius, source: CRC, Handbook of chemistry and physics, 91 edition.
All my other data are also listed in this book.
DCM might be a alternative for chloroform, if it's just a home experiment. (low bp is always nice)
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Nicodem
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I told you it would cause you frustrations, but it was not in vain as you learned something on extractions and partition coefficients. There is no way
you could extract any significant fraction of caffeine with a single ethereal extraction from water. You simply can not do extractions with
inappropriate solvents unless you do a continuous extraction. At least you found an efficient solvent to to remove the lipid and aroma fractions of
coffee. I posted something in regard to extraction solvent choice in another thread which you might find useful in your quest for the proper solvent.
Another thing you should do is to avoid coffee as a caffeine source. You should use some plant material that has a higher content of caffeine and less
other crap that can interfere with the isolation, such as tea. It has way less lipidic components and the crude product you obtain with the extraction
(with a proper solvent such as dichloromethane or ethyl acetate) is already mostly caffeine. All you need to do is to either sublimate or
recrystallize. There is plenty of information available if you just UTFSE. Caffeine from coffee is perhaps a tiny little bit too complicated for
beginners (it takes a little more work to purify the product).
Anyway, most of the issues discussed here were already discussed in one of the several previous caffeine extraction threads, but since some members
obstinately refuse to UTFSE: see here.
| Quote: Originally posted by arsphenamine | If you read some of the original recipes for Coca Cola, Pepsi, et.al., you see that they dissolved caffeine in aqueous phosphoric acid.
Caffeine's pKb is 10.4 -- low pKa values refer to the protonated form (conjugate acid). |
Aqueous pKa is the value you need here as it shows the acidity of protonated caffeine in water. It being 0.5 or 0.6 (depending on the source), it is
only little above that of water in water (-1.7). Such compounds only get considerably protonated at quite acidic aq. conditions (I would consider
about protonation only at pH < 2) which is obviously not the normal acidity of your average coffee or tea cup. As a side note, pKb is barely ever
used, because of its uselessness, as there is not much to compare it to (all dissociation coefficients were already unified to show the pKa only as
there is no reason to have two scales for acidity/basicity).
This quote from a pharmacology course (slide 26) nicely demonstrates this issue in its practicality aspect:
| Quote: | An oddity
Caffeine is a base drug, but it has a pKa of 0.5
pH – pKa = 3.5 – 0.5 = 3
Since caffeine is a base drug, we use the ratio backwards: unionized/ionized.
unionized/ionized = 103/1= 1000/1
In the stomach, caffeine will be mostly unionized, and fat soluble!
In the blood, caffeine will be even more unionized and fat soluble:
pH – pKa = 7.5 – 0.5 = 7, ratio = 107/1= 10,000,000/1. Caffeine is a 600 pound gorilla. |
Furthermore, just about any additive increases the solubility of caffeine and besides are you sure phosphoric acid was used for dissolution purposes?
I agree that phosphoric acid of proper concentration would increase solubility, but caffeine is already enough soluble in water as it is, so I wander
what the purpose would be.
The additive effect on solubility was already discussed in some other forum thread (UTFSE for more info). For example, sodium benzoate is commonly
added to increase solubility. The citrate anion and many others have a similar effect. Caffeine is also very prone to form charge transfer
interactions with other compounds and even several isolable complexes. Some complexes with acids can appear as salts even though they are not (e.g.,
caffeine nicotinate; compare that to urea non-salt "salts" as it has a similar pKa). On the other hand, its "normal" ionic salts such as the caffeine hydrochloride monohydrate,
hydrolyze to caffeine free base immediately upon dissolution in water.
| Quote: | | Alternatively, you allow the alkaline sediment to aggregate, filter it, and extract the solid residue with ethyl acetate. |
You have any references for such a procedure?
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Ozone
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DCM is the solvent of choice. Extract the free-base. Also, don't add salt, try washing with brine.
O3
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Hexavalent
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I would have to agree. DCM is also much safer than ether, due to its non-flammability (even though it is now labeled as a toxic chemical, but TBH what
isn't these days . . .) and in my experience seems to phase-separate more cleanly than ether.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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benzeentje
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First of all, thanks for all the responses. I was aware from the beginning that there are MUCH better ways to extract caffeine, i was just trying to
do it a safe and very easy way. I see your point that coffee isnt the perfect solution to extract caffeine from. Actually, it started to foam so hard
in the first place that all the layers were messed up. Furthermore, you really should have seen the visocosity of this solution. It was barely able to
decant it. The ether was very, very finely divedided in the coffee, as in a very strong emulsion, almost like mayonaise. I was only using ether
because someone told me that it works pretty well and has a very good Kd. Apperently he was wrong, if I read your very clear explanation. Thanks again
for the very detailed info. The fact that I used salt instead of Na2CO3 was simply because I had no Na2CO3 at home at a desired purity (even technical
would do I think).
For the part that DCM is safer, I must disagree. I worked at a lab where they used DCM as a solvent for a titration. Only very small quantities were
used, but when we worked with this, we always had to work under a fumehood. We even had to put a special gas mask on when we needed to put the !empty!
container outside in the chemical vault. Given that some people here in the forum claim that it isnt carcinogenic, i see your point. It was never
proven. But how do you prove carcinogenity? I'd rather didn't die for something like this. The fact that i used ether above DCM, chloroform or toluene
was actually in the first place a kind of safety measure. I'd not work with halogenated alkanes at home. I can understand that you use DCM or
chloroform in a lab, but even there we search for alternatives if possible. If there is no open flame or above normal temperature, ether is very safe
to handle.
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Hexavalent
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No, I believe you are misinformed. Unless you are working in your kitchen, DCM is very safe for home chemists with a dedicated lab space to handle it.
No fumehood is technically necessary if you have good ventilation. If heating is required, then it can be done under distillation without a fumehood
to capture the DCM. If that is not possible, work outside. At all times wear a lab coat or protective clothing, don a pair of goggles or glasses and
wear gloves throughout and you'll be just fine as long as you don't intentionally inhale the vapours.
Just because you inhale a few breaths of DCM, benzene or any other potential carcinogen, it does not mean you will immediately have cancer.
Ether vapours, however, can detonate when you flick the light off if at a sufficient concentration, and will obviously anaethetise in the appropriate
dosage and form.
You can get very pure sodium carbonate very cheaply from supermarkets as washing soda, it is known as washing soda and sold on the washing products
isle.
Carcinogenity is usually proven with lab animals, and predictions for humans are made based on what happens to them.
[Edited on 25-3-2012 by Hexavalent]
[Edited on 25-3-2012 by Hexavalent]
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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benzeentje
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I understand that you may feel safe to work with these chemicals, but I assure you that in my country, we take health concerns very, very serious.
Everything that may even look carcinogenic is unsafe here. Sometimes we are overcorncerned as well. For example, at my technical school, we weren't
allowed to use K2Cr2O7 in solid form, but in solution there was no problem. This meant that each time we had to use K2Cr2O7 (and that was a lot of
times =)) the teacher had to make the solution before we could handle it. DCM isn't proved to be carcinogenic. In fact, it is one of the safest
chloroalkanes to work with. But I would rather not have it in my kitchen. Acute carcinogenity is indeed usually proven by lab rats, but nobody knows
how our body will react in 20 years on DCM exposure. Few decades ago people washed their hands and lab tables with benzene. 10 years ago one could
even buy and use tetrachloroethylene here. Now all of this is forbidden to sell.
The problem with obtaining any chemical here is that I must drive quite a long time before I could find a grocery store here, and didn't think to buy
sodiumcarbonate in the other day. Another problem here is that almost all products here are mixed with other contaminations. For instance, one could
buy sulferic acid 30% as a drain cleaner, with only 1% contaminations, but the final solution has a black color and doesn't even slightly resemble
sulferic acid in viscosity or density. I think obtaining sodiumcarbonate in a pure enough form would mean a hunt on ebay and 2 weeks of waiting.
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Hexavalent
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Goodness, what country do you live in?
You should also consider finding a better place for your chemistry experiments than the kitchen, even if your new workspace is only temporary. Food
and lab chemicals are a dangerous mix.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Teen Chemist
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Caffeine extraction
I'm using xylene to extract caffine from an energy drink and I currently have it evaporating. Is there anything I could do to speed the process up or
should I just leave it.
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