Acetone crystallization of THC-A

This is a personal project of mine, one of many i hope to share over time with the community.
I encourage others to play around with this and other solvents, so we can get a better idea of
how we can isolate crystalline cannabinoids from raw oleoresins.

Crystallization of THC-A with acetone
This tek is to explore other possible routes of isolation of carboxylic THC, using acetone,
instead of a traditional non-polar solvent like butane, hexane, pentane, etc. Acetone tends
to be fairly volatile at room temp, and can be removed via vacuum and heat, over time, in a
vacuum oven. The strength of this is that we can remove the solvent without reaching temps
that will cause decrboxylation to occur, therefore, preserving the fragile compound we are after.
As long as there is no acids or bases with heat, there will be no side reacitons or isomerizations.
I have tested and confirmed this on my GC-MS, by running a sample before acetone dissolution, and after. The only changes were the removal of fats, narrowing the amount of compounds present, and increasing cannabinoid concentration per ml of oil.

First off, there are a few methods to end up with the same result.

Method 1:

  1. Freeze cannabis and acetone as cold as you can get it. the colder the better. fresh dry cured
    material is the best as it will have high THC-A content. (I havnt tried fresh frozen yet, im
    worried that water pickup would cause issues later in the process.)
  2. Quickly pass the solvent through the cannabis to extract the cannabinoids.
  3. Refreeze the solution for 24 hours to drop out any fats and waxes (Winterization). Acetone does not really like fats, thus they should be minimal.

Method 2:

  1. Take BHO and dissolve in acetone. A large amount of fats will drop out immediately, filter these at room temp.
  2. Freeze solution and filter, like a standard winterization. 24 hours at -25C does well for me.

Crystallization Steps

  1. Rotovap the solution around 35C under vacuum. this is important as you dont want to decarboxylate the material.
  2. When it becomes thick like syrup but still contains about 5-10% solvent shut er down.
  3. Pour the remaining solution into a mason jar or a crystallization dish. The key here is to have a “skin” form on the top of the oil/acetone solution so it slowly releases the solvent over time.
  4. The solution will decrease in volume over the next day or 2, depending on the room temp.
  5. Take a sterilized needle or glass rod and scratch the bottom of the dish to create nucleation sites.
  6. Do not agitate or move the dish from this point on. Less movement = More defined crystal formations.
  7. Let it sit in a dark place around 18C for a week or 2. Crystals will form on the glass underneath the oil. They will eventually stop growing and stall out allowing you to pour off the terp/cannabinoid sauce on top.
  8. Remove the best looking cluster, and redissolve the crystals that remain by adding a small amount of fresh acetone over a couple hours with no mixing or agitation.
  9. Re-nucleate the solution by evaporating the solvent off in the crystallization dish at room temp until gets a skin again, or re-seed with your collected crystals from before.

This step can be challenging because if you add them too early it will dissolve them too.

  1. Let it do its thing. Its best to kinda leave it for a while and forget about it. This tek is not for impatient people.

Alternative methods i have played with:

  1. Pour butane rich oil from closed loop into a mason jar.
  2. Let evap for a bit until it is thick.
  3. Put on lid and wait 14 days.
  4. Small crystals will crash out and stay on bottom of the jar.
  5. Open jar and pour off sauce layer.
  6. Dissolve crystals and start at method 2 above.

This concentrates THCa right off the bat, allows for faster work.


does it matter what type of Acetone used? i can only assume lab grade but would acetone from home depot be ok swell? thank you for the SOP


I’m just starting my journey and I’ve been making iso shatter. I’m using all the knowledge I can get my hands on so thank all of you who have come before and paved/paving the way for these cool new experiments for me anyway.
I would also like to know what type of acetone should I buy? I’m ready to go diamond mining.


For experimentation i used acetone from the hardware store. If you were to consume them i would use known quality solvents if possible.


Do not use anything less then USP grade. Home Depot and similar acetone has peroxides and other shit.


I agree. For research, utility grade solvents are a good place to start but please for the love of cannabis nobody use anything less than USP grade solvents from approved sources for any type of consumption.

Great point to make


It’s worth checking FDA solvent classes as well. Class 3 (butane, ethanol, acetone, pentane etc. etc.) are all relatively benign.

You get into class 2 (MeOH, DCM, TCM, ACN, Hexanes etc.) and these compounds are getting nastier. FDA reccomends the pharmaceutical industry avoid their use wherever possible, and levels in final products must be strictly controlled.

Class 1 solvents are the ungodly nasty ones. Benzene, CCl4, dichloroethane & ethene. These compounds are so nasty that their use in pharmaceutical science is widely discouraged, unless a drug with significant therapeutic advances can only be made with the use of one of these solvents.

This is of course a separate issue to purity, but also worth considering in a thread where we’re encouraging people to play around with different solvents I think.


So I assume that you do not close the mason jar as we want the evaporation of the remaining solvent to happen?


Yes. I have experimented with lidding a jar on and off. The process stalls out to a degree if it sits too long with no evaporation. Restarts if you remove the lid. The crystals in the picture above were in a petri dish, no lid. My shop temp is usually around 16-18°C.


Acetone is capable of forming peroxides, however unlikey. Peroxides are explosive. Acetone peroxide is a very unstable high explosive called tatp. I doubt they would form, even after years of storage with oxygen. Ether, however; will form peroxides by its self. A very dangerous solvent if you don’t know what your doing. It is usually made fresh and used immiditaly, people tend not to store it for that reason. Nothing like twisting the cap off a bottle and having it explode.


Having played with TATP, i know that it generally required a catalyst (acid) to get the reaction started to create them. If done above 10°c it makes di-acetone-tri-peroxide, which goes off if you look at it funny.

It did generally require certain concentrations of h202 in the mix to make though.

Still a valid point to make, but i think highly unlikely to occur unless you were using acid in your process prior.


im experimenting with co2-expanded ethanol (CXE) at < -50c. then possible an acid/base extraction of thca using water


Less than 30% H2O2 and the reaction simply doesn’t have enough oxygen. Original discovery was made in 1895 where small crystals were seen developing in a mixture of acetone and H2O2 which sat at room temperature for a week.

I agree. Highly unlikely, especially without the presence of an acid catalyst (we always went for H2SO4). Certainly no reason to discourage further experimentation.


If i could like this 2x i would :joy:


11643514fnl_Q3CTablesRev3.pdf (185.2 KB)

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u should experiment with putting dry ice in ur acetone to both chill it and dissolve in co2. co2 seems to dissolve into polar solvents at cold temps. and co2 would expand the volume, make the acetone less polar and it would also increase the mass transfer ratio. I don’t whether that will mean any drastic difference but it would be an interesting experiment. im experimenting with co2 expanded ethanol and many of the papers mention co2 expanded acetone as well


"Shishikura and coworkers
successfully separated citric acid from other organic acids in a CO2-expanded acetone
solution (Shishikura et al., 1994), indicating that GAS precipitation may be a promising
method of separating fermentation broths. "

and by separated they r refer preferentially crystallized


I followed this Tek. I started with BHO and dissolved in acetone and then froze/filtered. I just started to get some crystalization after a few days. Will update with pictures as soon as they grow larger.


I’m basically at this step right here, have some bho that either is improperly dewaxed/winterized and trying to turn it into headstash… excited to hear back from u.

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hello me my question is is it possible to cause crystallization from rosin and if so how? and any solvent and counter solvent must be used?
as far as I’m concerned I have neither labglass nor specific extractor ^^’