Introduction
Acetone is often used to 'wash' MDMA.HCl, i.e. to reduce the amount of pollution before re-crystallization. See MDMA/ecstasy purification method. It's difficult to find data on solubility, probably because of the legal status in many countries. Using this data one can make better choices, e.g. how much solvent to use or at which temperature to wash.Experiment 1
203.3 mg pure (84% MDMA in) MDMA.HCl was dissolved in 20.0 mL dry acetone at 51°C, then cooled and decanted at RT, 8°C and -18°C, remaining crystallized fraction weighed.Results 1
Measured fractions:A: 82.6 mg at 24°C
B: 39.6 mg at 8°C
C: 24.8 mg at -18°C
D: 57.9 mg yellow crystal after distillation + re-crystallization in IPA
E: 2.3 mg yellow-brown oil
sum: 207.2 mg
Calculation of solubility
| Temperature | Solubility | Calculation |
|---|---|---|
| 24°C | 6.04 g/L | ( 203.3 - 82.6 ) mg / 20.0 mL |
| 8°C | 4.06 g/L | ( 203.3 - 82.6 - 39.6) mg / 20.0 mL |
| -18°C | 2.82 g/L | ( 203.3 - 82.6 - 39.6 - 24.8 ) mg / 20.0 mL |
Due to evaporation the denominator will be a bit lower, so solubility at -18°C and 8°C will be higher.
More accurate would be to publish mol/mol because the density of the solvent will vary at different temperatures.
Experiment 2
301.1 mg pure (84% MDMA in) MDMA.HCl was dissolved in 20.0 mL freshly dried acetone at 52°C, then cooled and decanted at RT, 8°C and -18°C, remaining crystallized fraction weighed.Results 1
Measured fractions:A: 199.4 mg at 22°C
B: 39.0 mg at 8°C
C: 24.1 mg at -18°C
D: 35.3 mg after distilling, decanting, drying
Total: 297.8 mg ( 3.1 mg missing)
Calculation of solubility
| Temperature | Solubility | Calculation |
|---|---|---|
| 22°C | 5.09 g/L | ( 301.1 - 199.4 ) mg / 20.0 mL |
| 8°C | 3.14 g/L | ( 301.1 - 199.4 − 39.0 ) mg / 20.0 mL |
| -18°C | 1.93 g/L | ( 301.1 - 199.4 - 39.0 - 24.1) mg / 20.0 mL |
| 52°C | >15 g/L | 301.1 mg / 20.0 mL |
Discussion
The difference between 1 and 2:23°C: 0.95 g/L
8°C: 0.92 g/L
-18°C: 0.89 g/L
can be explained by a slightly higher water content in the first solvent.
Note that the error margins are probably too high to draw any conclusions from the differences at different temperatures: i.e. they could be all the same (within the error margin)
If the solubility of MDMA in water is 1 kg/L, this means that the first solvent contained 18 μg (= 0.1% by mass) more water than the solvent used in the second experiment.
Note that the amount of water in the second experiment is unknown. The lowest solubility of all experiments will be closest to the real values.
Wash at room temperature (RT) ?
Since the solubility at 22°C or 24°C is still quite low I propose to wash at RT. You probably do not wash the dishes in cold water: A warmer solvent generally washes better, at the cost of some of the product (which mostly can be recovered).The difference is 3 gram per liter (-18°C vs 22°C), so if you use 4 mL for every gram MDMA.HCl, you'll lose 12 mg per gram MDMA extra or 1.2% per wash.
By cooling/freezing in a non-dry atmosphere it's very likely that you'll introduce water (condensation) into the solvent, with possibly a higher loss.
If there was still a significant amount of water in the second experiment, then the solubility is lower, so the loss can be even smaller.
I do not know the solubility of the pollution at various temperatures, so I cannot say how much washing at higher temperatures helps.
How much water affects the result
If 1g MDMA dissolves in 1 mL water, then 1% water in the acetone (which is quite common) will dissolve 15mg per mL: 10mg in the water and 5mg in the acetone.NOTE: I do not have a reliable source for the solubility of MDMA.HCl in water, but read some estimates above 1kg/L.
Possible error causes
- evaporation of acetone
- tiny crystals in the decanted solution
- volume of acetone: 20.0 error 0.1 mL (2 x 0.05 mL)
- weights have an error of 0.6 mg due to subtraction
- evaporation of acetone in the first erlenmeyer after decanting: some 48 mg = 0.06 mL
- inclusion of acetone in the MDMA crystals : not relevant
- density of acetone at 24°C (vs documented 20°C)
- grease on the NS ground joint (wiped before decanting)
- slow crystallization: how long to wait?
- MgSO4 from the dry acetone in the "MDMA"
- tare weight of the erlenmeyer: easily a mg more by touching it