liquidcrawler
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Dichloromethane substitute?
Hello everyone, I am a student in need of your help! I am conducting a project for my chem class where I extract caffeine from tea leaves. Its basic,
I know. However, I have a problem I was hoping you all could help me solve. The experiment I am using calls for dichloromethane (a.k.a. DCM,
methylene chloride, or CH2Cl2) and my teacher has run out of stock of it. I need it as a solving agent to extract the caffeine, so the question I am
asking is; Is there a substitue I can use instead of dichloromethane, or, is there a way I can distill it? (The experiment I am following is contained
here)
Thank-you and all answers are appreciated!
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Bot0nist
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Mood: Streching my cotyledons.
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Try ethyl acetate maybe.
Also, your teacher just expects you to find D.C.M. otc to do this lab? That sounds pretty unusual. I think it could be easily distilled if you can
find a paint stripper or plastic adhesive that has a suitable amount in it. Though it seems increasingly harder to find...
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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liquidcrawler
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Thanks a bunch, my teacher did have it at one point, howevershe has run out at has told me to do a different project instead, and I being as stubborn
as I am, am dead set on doing this piticular experiment. I am fairly certain I saw ethyl acetate in stock.
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HydroCarbon
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There's a multitude of solvents you could use for this. The main thing you want though is for your solvent to be immiscible with water. So you can
properly extract the caffeine and leave behind other compounds in the water.
Mix your tea with a relatively small amount of pH 3 or lower HCl solution, something like 500mL of water per 100mL of dry loose tea, mix it well using
a stir plate for about 30min. Then filter out the solid tea, a coffee filter works good for this; lab grade filter paper tends to get clogged easily
if you're not using vacuum.
After removing the solid tea, put your water solution back on the stir plate and add NaOH to the stirring solution to bring the pH above 12, let this
stir for 10min. Then pour the whole solution into a separatory funnel.
Now you add your organic solvent. I would suggest toluene, xylenes, ethyl ether, or chloroform. Extract using multiple small portions of solvent.
For example if you have 500mL of water solution, extract with 5 fresh 25mL portions of solvent.
After solvent extraction you can now gather your caffeine. To get it out of the solvent you could do one of two things. One you could add
concentrated HCl-(aq.) dropwise to the solvent, this should cause pure caffeine to precipitate out of solution, then you can gather it by filtration.
The other thing is you could do is evaporate your solvent (don't do this with ethyl ether), then purify the resulting powder by recrystallization in
isopropanol.
This is called an acid base extraction, here is some background info:
http://en.wikipedia.org/wiki/Acid_base_extraction
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GreenD
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A fairly general method is interesting:
In coffee there is an art to making the best! The thing is when hot water is poured over coffee, three compounds tend to come out at different times.
The first tends to be sugars and the like (The hotter the water extraction, the better)
Second to solvate is the caffeine and related compounds.
Finally, the third compounds that come out are tannins and bitter - compounds.
Hence, a good coffee maker is hard to come by - and most machines give you just 'average coffee'
(more expensive coffee machines!) I always wondered why I would ever want a 200$ coffee maker - well they make a difference. They are made by the
pros.
So, if you wanted to go against the books you could try running an aqueous solution through tea (or coffee) and collecting fractions, then either do
a/b extraction or rotovap (rotovapping water is sometimes annoying depending on the lab equipment).
Just an 'out of the box' suggestion.
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chemrox
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Use ether- I extracted caffeine from instant coffee with ether as a first or second lab in Chem 112a
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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ItalianChemist
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Hi!
I'd like to perform this reaction: http://courses.chem.psu.edu/chem36/Chem36H/IndivExpt1/801%20...
But I don't like very much working with DCM, is there a substitute for it(except dimethylformamide)
Thanks!
[Edited on 28-5-2011 by ItalianChemist]
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Nicodem
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DMF can not be used in that reaction, because it dissolves water and NaOH, forming a monophasic system (the ylide can hydrolyse). Try with toluene.
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ItalianChemist
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Quote: Originally posted by Nicodem  | | DMF can not be used in that reaction, because it dissolves water and NaOH, forming a monophasic system (the ylide can hydrolyse). Try with toluene.
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Ok thanks,
Oh i saw the same synthesis with DMF, maybe I read wrong
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Nicodem
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Are you sure it was with aqueous NaOH, or was another base used? Could you please find the article where you saw that and check? I would like to see
how resistant is that benzylidene ylide toward hydrolysis. Ylides made from alkylphosphonium salts generally hydrolyse practically instantly in
contact with water. If you find an example where NaOH was used in an Witting with such reactive ylides in a homogeneous solution, it would be quite
interesting to me.
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ItalianChemist
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| Quote: Originally posted by Nicodem |
If you find an example where NaOH was used in an Witting with such reactive ylides in a homogeneous solution, it would be quite interesting to me.
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Versuschemie, if I am not wrong!
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Nicodem
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Found it: http://www.versuchschemie.de/hartmut.php?t=7063&sid=3dac...
Quite surprising results, I would say. Chris, the author of the experiment, comments in regard to the demonstrated ylide resistance toward hydrolysis:
| Quote: | | Damit man die Synthese erfolgreich durchführen kann, muss man unter wasserfreien und am besten auch sauerstofffreien Bedingungen arbeiten, weil das
Wittig-Reagenz recht empfindlich gegenüber diesen möglichen Einflüssen reagiert. Dies ist aber in diesem Beispiel nicht erforderlich. Als
Lösungsmittel verwendet man polare aprotische Lösungsmittel, wie Dimethylformamid(DMF) oder Dimethylsulfoxid(DMSO). Mit DMSO könnte man man auch
versuchen, das giftige DMF zu ersetzen. Wie schon eingangs erwähnt, erzeugt man das Wittig-Reagenz durch Deprotonierung mit einer starken Base. Im
Normalfall, so wie es auch in einer Allgemeinen Arbeitsvorschrift im Organikum beschrieben wird, wendet man für diesen Zweck Natriumhydrid oder
Phenyllithium an. Bei den besonders gut stabilisierten Triphenylphosphoniumsalzen kann man aber auch auf weitaus ungefährlichere und daher auch
leichter handhabbare Basen zurückgreifen. In diesem Beispiel war bereits der Einsatz von konzentrierter Natronlauge(50%ig) ausreichend. In manchen
speziellen Fällen wird sogar die Verwendungsmöglichkeit von Natriumcarbonat (!) geschildert. Vorschriften dazu finden sich z.B. im Gattermann.
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…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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ItalianChemist
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mmmh but he obtained only 65% yeld...
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Nicodem
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Two references on the topic of Wittig reaction in (presence of) water:
Wittig reactions in water media employing stabilized ylides with aldehydes. Synthesis of alpha,beta-unsaturated esters from mixing aldehydes,
alpha-bromoesters, and Ph3P in aqueous NaHCO3.
J. Org. Chem., 72 (2007) 5244-5259.
Aqueous Wittig reactions of semi-stabilized ylides. A straightforward synthesis of 1,3-dienes and 1,3,5-trienes.
Tetrahedron Letters, 50 (2009) 5737-5740.
The first article is not particularly surprising as it deals with very stabilized ylides. But the second one is about allylphosphonium derived ylides
which are just about as stabilized as the benylphosphonium derived ylides mentioned above of successfully compete with hydrolysis in a Wittig
reaction.
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The WiZard is In
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| Quote: Originally posted by liquidcrawler | | Hello everyone, I am a student in need of your help! I am conducting a project for my chem class where I extract caffeine from tea leaves.
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Not that many years ago decaffeinated coffee was made using
trichloroethylene, which you at that time buy in most any
hardware store, it had replaced carbon tet when CCl4 was declared
carcinogenic. When trichloroethelene was declared to be a
carcinogen it was replaced (not for DeCaf coffee) by
1,1,1 trichlorethane, which when it was ........ replaced by nothing.
DeCaf is now made using supercritical CO2. A quick check of
www.justfuckinggoogleit.com search mentions
ethyl acetate being used in Europe.
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samuelferreira
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***Looking for TCE replacement, or Methylene chloride replacement or TCA replacement or 1.1.1:
Check out GenTech, it works really well as a direct replacement and it is non-flammable.
People use it in vapor degreasing and ultrasonic units.
http://www.relspec.com/solutions/trichloroethylene-replaceme...
***looking for nPB replacement:
Check out AeroTron, it works as well, has a better H&S profile and it is non-flammable.
AeroTron can be used in vapor degreasing, ultrasonics cleaning and as a wipe also.
http://www.relspec.com/products/aerotron/aerotron-overview.h...
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