This question gets asked a lot around the place so I thought I would copy 'LeJunks' guide here for everyone to see.
Please note that this procedure will not give you anything that you haven't already started with, it has nothing to do with synthesis and all it explains is how to seperate caffeine from your product.
Massive resped to 'LeJunk' for making this guide and I hope that they are fine with me copying into this section. (the site that I copied this from insists on the SWIM reference)
Last night SWIM took some yellow Louis Vuittons and they felt like anything other than pure MDMA, though they certainly tested well for it with the EZ Extreme. Afterwards, SWIM could only attribute the experience to that of MDE, though SWIM really didn't know for sure. The problem, as most of you are aware, is that there is no test to differentiate between MDMA and MDE. And the problem with that is that one of those two is great while the other is, well, crap!
All day long SWIM was going back and forth wondering if it was indeed MDE or perhaps caffeine, seeing as how there's no test for that either. After agonizing over it for hours, SWIM decided to perform a simple anhydrous (water free) acetone wash on 4 pills. Caffeine is entirely soluble in acetone while MDMA is not. Therefore, you'll simply be rinsing the caffeine right off of your pills, or I guess powder at this point.
SWIM will outline below how to make hardware store acetone anhydrous by the use of epsom salts turned anhydrous magnesium sulphate with heating. But may SWIM strongly suggest that you just skip that and simply order lab grade anhydrous acetone via a chemical supply company. It's much better quality and it's not that expensive either. Nor is it a watched item. SWIM would order a 1 liter bottle, it's all you'll need for awhile.
If not, you can make simple hardware/home store acetone anhydrous with the following directions:
When using 4 tabs as the control, take a tall shot glass or a 50 ml. glass beaker and fill it to 20 ml.s with anhydrous acetone. If you don't have anhydrous acetone, simply go to Home Depot, Menards, or Lowes and purchase a 1 liter can of acetone in the paint section. Also grab a bag of epsom salts. When you get home, spread some epsom salts out onto an aluminum covered baking sheet. Bake the salt for 2 hours at 400 degrees F. At the two hour mark, you should now have a greyish looking ash, better known as anhydrous magnesium sulphate. Scrap up about 15-20 grams of the magnesium sulphate ash and pour it directly into the can of hardware store acetone. Once it's all in, replace the lid and shake vigorously for about 5 minutes. This will insure that the magnesium sulphate has completely absorbed any and all of the water/alcohol that's in the hardware store acetone. Let stand for 24 hours to insure that all of the mag. sulphate has fully absorbed all of the water/alcohol and has thus sunk to the bottom of the can. Once done, never pour from the can again. We want that pile of goo, now at the bottom of the can, to stay there. So therefore, use a glass eye dropper to get down inside of the container to extract the acetone as needed. Now you're ready to go! If you already have lab grade acetone, then you will start from here as well...
Pour 20 ml.s of anhydrous acetone into a 50 ml. beaker and add your finely chopped pills, now powder, into the acetone. Stir thoroughly for about 2-3 minutes. Cover and let settle. Let the acetone on top become clear while the molly crystals mixed with some acetone insoluble cuts lay on the bottom. Once settled, carefully pour out the top layer of now dirty acetone stoping just short of any powder falling into the filter. Cover the filter and repour 10 more ml.s of fresh acetone into the original beaker still containing your mostly MDMA crytals with a little residual flat powder stuck to the side from the original pour. Cover and let settle. Once again, carefully try and pour into the original filter, just the flat powder looking substance stoping just short of the crystals. This time, you should have at least 98% pure MDMA crytals left in the beaker, and just a trace of powder still, if any.
Remove, but don't throw away the original filter paper. Replace with a fresh new filter paper, swirl the final washing and pour the entire contents into the new filter paper. Cover. Pour a little fresh acetone into the beaker to gather any remaining crystals and pour them into the fillter paper. Cover and let drain thoroughly. Remove and press the filter paper containing the nearly pure MDMA crystals inside in between a few paper towels to absorb any excess acetone. Preferably leave inside of the filter paper and let air dry in a non-humid environment for at least 48 hours. Once evaporated for 48 hours, simply divide the pile of powder into 4 seperate piles (the number of original pills that went in) and consider each pile one seperate hit. There is no way short of GC/MS testing to determine the actual mg.s per pile, but there is exactly the same amount of MDMA per pile as there were per tablet before this procedure started. Therefore, if you normally take 2 pills out of the shoot, then you should now consume 2 piles out of the shoot. That's it!
Please not that this procedure is simply to remove caffeine.