[Yggdrasil]

Mark, I read through your post on the extraction of caffeine and I noticed something that I may have missed before.  What did you use for the dcm extraction?  Did you extract the caffeine from the filtrate (the liquid remaining after the solid has been filtered out) or the precipitate (the solid stuck to the filter)?  You should extract the caffeine from the aqueous liquid which remains after filtration.  If you extracted from the precipitate, that explains why you got an emulsion since the tannin salts may be soluble enough in dcm to create an emulsion.

[Mitch]

Sublimation should be fine as the final purification step.

[pantone159]

Mark, I read through your post on the extraction of caffeine and I noticed something that I may have missed before.  What did you use for the dcm extraction?  Did you extract the caffeine from the filtrate (the liquid remaining after the solid has been filtered out) or the precipitate (the solid stuck to the filter)?  You should extract the caffeine from the aqueous liquid which remains after filtration.  If you extracted from the precipitate, that explains why you got an emulsion since the tannin salts may be soluble enough in dcm to create an emulsion.

I extracted from the aqueous layer, but I did try and wash the precipitates with DCM first.

In lieu of pouring DCM through the precip in the filter paper (which wouldn't have worked), I dumped the ppts into a beaker, then added some DCM.  A glob of (presumably) H2O collected on the surface, with the DCM underneath.  I was mostly able to decant the DCM by itself, keeping the H2O and solids in the beaker.  I poured this through a filter, which eventually clogged up when the water got there. 

This left me a completely clear, colorless filtrate of DCM, presumably containing any caffeine that was trapped in the filtrate.  This became my first portion of DCM used to extract from the aqueous layer.  I repeated the extraction 2 or 3 more times with fresh DCM.

I evaporated these combined DCM extracts to yield the crystals.

[Will]

Can you get acetone at the hardware store?

Ah! of course! I checked my local hardware store (ebay!) and they sell pure acetone for £19.99 per 5L- don't think I'll get it yet though.

I think you want to add some Ca salt because Ca tannate is especially insoluble.

Should've guessed that was the reason- makes perfect sense! Should I go to the trouble to find some cheap barium salts like barium hydroxide (found 100g BaCO₃ for £5.72) as I assume that would be more effective? I only have about 8 spatula measures of Ca(OH)₂ anyway- I am useless at estimating masses- my scales (accurate to nearest mg apparently ) should arrive wednesday, and I decided on big fat cheap safety glasses which should also arrive on wednesday, and if the chemicals arrive tuesday or wednesday I should be set to go on the wednesday!

My sublimation plan was to use what would be a Buchner fiter setup (I have a hand pump whose effectiveness is yet untested), but putting an ice filled test tube where the filter would usually go, in the adaptor in the mouth of the filter flask.  I might not have a fat enough tube to get a good seal, we shall see.  Put the caffeine in the bottom of the flask, and hope it condenses on the ice filled tube.

Excellent idea! I ordered this Buchner funnel set-up a couple of weeks ago: http://www.onlinesciencemall.com/Shop/Control/Product/fp/vpid/2228961/vpcsid/0/SFV/30852 and should be arriving soon but have no idea what size the hole for the funnel is in the stopper. I have 16mm and 24mm 'inside' diameter test-tubes and if they fit I will do it that way. My only dislike of that method is the chance that the caffeine would deposition (?-gas to solid) on the wall of the conical flask (me being pesimistic?!) - that is why I thought of the beaker method because if that did happen I could recover it- that precious 1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione!

[pantone159]

Should've guessed that was the reason- makes perfect sense! Should I go to the trouble to find some cheap barium salts like barium hydroxide (found 100g BaCO₃ for £5.72) as I assume that would be more effective? I only have about 8 spatula measures of Ca(OH)₂ anyway- I am useless at estimating masses- my scales (accurate to nearest mg apparently ) should arrive wednesday, and I decided on big fat cheap safety glasses which should also arrive on wednesday, and if the chemicals arrive tuesday or wednesday I should be set to go on the wednesday!

I ordered this Buchner funnel set-up a couple of weeks ago: http://www.onlinesciencemall.com/Shop/Control/Product/fp/vpid/2228961/vpcsid/0/SFV/30852 and should be arriving soon but have no idea what size the hole for the funnel is in the stopper. I have 16mm and 24mm 'inside' diameter test-tubes and if they fit I will do it that way. My only dislike of that method is the chance that the caffeine would deposition (?-gas to solid) on the wall of the conical flask (me being pesimistic?!) - that is why I thought of the beaker method because if that did happen I could recover it- that precious 1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione!

I got a very similar Buchner setup, but a little bigger, they didn't have the 250 ml size when I shopped.  (At least, in the alternate universe where I am not in Texas.  As it is, I had to settle for some glass and ceramic beakers that look a whole lot like such a Buchner setup.   )  I will try a 20mm dia tube, it may be too small however.  I think 25mm dia is too big.  24mm *might* work, 16mm would be too small for the adaptor I got.  It might work with the smaller size, though.  Something like 22mm might be perfect for mine, I didn't find that size, however.

I don't know if Ba would work.  Like I said, I don't know my tannate chemistry very well.  I used CaO, but it would be interesting to know if Sr or Ba salts would work as well.  (I don't think I'll try Ra salts!)

I think I have a spatula that is long enough so I could scrape the stuff of the inside of the flask, but I haven't really checked to see if it would work.  At worst, I could re-dissolve the crystals and re-evaporate.

[constant thinker]

Can you get acetone at the hardware store?

Check the paint section of Home Depot if you guys have it down there in Texas. I found what appeared to be pure acetone. The ingredients only listed acetone.

[pantone159]

I found another lab procedure for a caffeine extraction in "Experimental Organic Chemistry", Durst & Gokel, 2nd ed.

They extracted the caffeine with an aqueous Na2CO3 solution, then extracted the caffeine with dichloromethane (DCM).
This procedure specifically warned that this system is likely to form very troublesome emulsions, so you should mix gently.  On the other hand, I was following the advice from another book re sep funnel usage, "Really shake it!!".

One question:  The book had this as a problem, with no answer:
Why would you extract with a basic solution?  I would expect that, in acid, the N on caffeine gets protonated and the result is more soluble in water, than when the N is not proronated.  Using the basic solution did seem to work, but I don't understand why acid wouldn't have been preferred for the extraction.