Boffis
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Theobromine extraction
You can buy from the internet cocoa bean extract that claims to be 40% theobromine. So I bought some and tried the method depicted in a youtube video
increasing the amount of MgO to account for the lower fibre content and presumably higher fat content (the powder has a greasy feel to it) and
simlarly increased the solvent ratio. However, I could only extract of soft greasy white fat and only traces of anything crystalline.
So has anybody every tried this extraction or played around with with cocoa extract? Theobromine is sparingly soluble in alcohols so I had tried
dichloromethane but this seems to extract mainly the remaining fat. The fat content is a lot less than in raw cocoa.
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Metacelsus
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In my undergrad analytical chemistry class we extracted theobromine from chocolate. I'll see if I can find the protocol.
OK, here it is:
1) Grind 500 mg chocolate into powder. (Also prepare samples spiked with known quantities of theobromine in order to determine % recovery)
2) Remove the fats by extraction into 10 mL petroleum ether. Centrifuge and remove supernatant.
3) Air dry the pellet, then resuspend in 30 mL of 20 % methanol by volume in water, and heat to reflux for 5 minutes.
4) Vacuum filter, then adjust volume back to 30 mL.
After this, we proceeded to use reverse phase HPLC to quantify the amounts of theobromine in solution. The amount extracted was 58 mg +/- 2.2 mg
theobromine per 500 mg sample of Hershey's Special Dark. The spike recovery was 96%.
Edit: Of course, extracting theobromine is not the same as isolating it. If you want to do that, concentrating the solution and trying a
recrystallization might work.
[Edited on 2019-8-1 by Metacelsus]
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Boffis
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@Metacelsus, I liked your idea about extracting the material with petroleum ether first so I tried this on a small sample (2.5g). I extracted it twice
with about 3x its weight (about 10ml) of low boil petroleum ether (40-60 C) and left it to dry. This initially gave me a brown free flowing powder but
after some time it became damp and by this morning had turned into a toffee like mass but this suggested that it is partly soluble in water. So I
stirred the toffee like material into 12ml of water and boiled it briefly then left it to cool. Most of the material dissolved to give a cloudy brown
solution and a heavy granular off-white precipitate. I am currently trying to filter it but it filters very slowly. Assuming any theobromine is in the
precipitate and since it settles quickly I may try simply decanting it if I do this an a larger scale.
My plan is to dissolve the precipitate in 1M NaOH, in which theobromine is supposed to be soluble to the extent of about 5g per 100ml, and then
precipitate it with dilute acid. Finally I will recrystallise it from a suitable solvent. Does anyone have any information on what is a suitable
solvent? In the youtube video they used DCM as the solvent but simply evaporated off the solvent rather than let it crystallise?
I ended up having to decant the brown liquor from the whitish precipitate as it would not filter even under strong vacuum. I washed the precipitate by
decanting again and then filter the residue. I have about 0.1-0.15g drying
I have run another batch with 10g in about 90ml of water and 10ml of 30% HCl. I heated it almost to boil and left it to cool. When cool I will
neutralise the acid and chill it. I will then see if the acid treatment has made the aqueous liquor easier to filter (I suspect there is a starch like
material in the extract). I white ppt has already formed.
[Edited on 2-8-2019 by Boffis]
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Boffis
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Well, I have run several more small batches and it is becoming fairly obvious that the theobromine content is small.
I leached another 10g with 50ml of hot water and allowed it to cool, this resulted a cloudy brown solution that difficult to filter but could be
decanted from the granular heavy residue that weighed <0.3g. 50ml of water at room temperature could dissolve only 0.025g of theobromine so there
should be at least 4g of residue.
To make the aqueous leachate more filterable I tried leaching 10g with petroleum ether first, dried it and leached it with water but it still gave a
difficult to filter leachate and a little granular residue.
I tried leaching another 10g with 1M sodium hydroxide (100ml), treating it with charcoal, filter and then neutralise with 28% HCl. A small amount of
dark brown flocculant precipitate formed but again the amount was very small.
My conclusion is (once again) that the so-called extracts available on line are highly suspect and the claims about content are often somewhat
doubtful. In this case I think that the bulk of the extract (>90%) is water soluble sugars and dispersable starchs. The theobromine content is no
more than 3% and there is a similar amount of fat and little volatile oil.
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draculic acid69
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Theobromine is just methyl caffeine right?
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Metacelsus
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Other way: caffeine is theobromine with an extra methyl group.
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Boffis
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I have just completed another batch of 10g. Extracted with petroleum ether twice to remove fats, then leach 50 ml of water decanted and the residue
drained on a Buchner funnel. The cake was dried and leached with 2x 100ml of hot DCM. The DCM was distilled off until only a small volume remained and
after cooling diethyl ether was added as in Nilered's video, filtered and the cake dried to give just 90mg of off-white residue (theobromine?).
Extraction the the original residue with another 100ml of DCM gave no further measurable yield. This is a yield of only 0.9% about what you would
expect from straight cocoa powder. I now think that the material is actually just de-fatted cocoa powder and not an extract at all. I am now totally
satisfied that the material is rubbish left over from the preparation of cocoa butter.
Metacelsus is right; theobromine has one less methyl group attached to the six membered pyrimidine ring than caffeine. My interest in it is that if it
undergoes the same degradation under the infulence of chlorine as does caffeine then it would offer an OTC route to 1-methylbarbituric acid,
1-methylalloxan and N-methylvioluric acid. These compounds are also accessible from caffeine by a complex route.
Just weighed the residue from the evaporation of the petroleum extract and got 12mg from 10.040g of "extract". The loss of weight of the extract after
the pet ether extraction was 294mg so I was surprised how little fatty material was present, the difference is probably water that is lost by the
extract at the same time.
[Edited on 6-8-2019 by Boffis]
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