# Solubility experiments



## 84% (Sep 26, 2022)

Let's start a thread on how to measure solubility in general. For specific substances and solvents better start a separate thread, since most readers are probably more interested in the results than in academic discussions.

Why?​Knowing the solubility at various temperatures helps:

determine the yield vs loss in advance
optimize crystallization or washing
know how much solvent has to be used
select an acceptable temperature (range)
How?​Solubility generally increases with temperature, so we have two options:

dissolve at _low_ temperature until saturation and _increase_ the temperature: add more crystals
dissolve at _high_ temperature just below saturation and _decrease_ the temperature: decant the saturated solution
The second probably works the best: all the time keep the solution saturated and remove the crystals.

For *MDMA in acetone* I made an estimate of the solubility from existing lab notes, 8 or 9 g/L at room temperature, and then devised an experiment:

S1.) dissolve 200.0 mg (S) pure MDMA.HCl in 20.0 mL dry acetone at 40+°C. (=> if all dissolves: 10g/L)
S2.) cool to room temperature (RT) and decant
S3.) dry the crystals and weigh them => fraction A
S4.) cool the saturated (decanted in S2.) solution to 8°C and decant
S5.) dry the crystals and weigh them => fraction B
S6.) cool the saturated (decanted in S4.) solution to -18°C and decant
S7.) dry the crystals and weigh them => fraction C

Decanting is easy because the crystals grow on the glass wall.

From these results the solubility can be calculated:

RT : (S - A) / 20.0 mg/mL
8°C: (S - A - B) / 20.0 mg/mL
-18°C: (S - A - B - C) / 20.0 mg/mL

See MDMA.HCl solubility in acetone for the results.

Note that this is the upper bound: it measures the amount that was forced out of the solution due to the cooling.

The same experiment for IPA (2-propanol, CAS 67-63-0) would be:

S1.) dissolve 4.00 gram (S) pure MDMA.HCl in 12.0 mL dry IPA at 75°C. (=> if all dissolves: 1g in 3 mL)

From lab notes I've calculated that 95% is crystallized at 12°C and about half at 40°C, but the amounts were not accurately measured so this is a very rough estimate. Adjust the amounts to available equipment to minimize errors.

Literature​MDMA.HCl in some solvents, but not in acetone or IPA:

3,4-MDMA (hydrochloride) (3,4-Methylenedioxymethylamphetamine, NSC 168383, CAS Number: 64057-70-1) | Cayman Chemical


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