Solubility Studies 1: Salts & Salting Out - Guide to Enhanced Techniques Options
#1 Posted : 11/19/2019 7:54:49 AM

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Hi All,

I've started working on a series of solubility studies aimed at perfecting the art of crystallization. This part is based on a solubility study I did on fumaric acid, in solutions of water, acetone (undried and dried) and ethanol. I found that the solubility of fumaric acid in even anhydrous acetone is still fairly low, and I devised a new salting method which takes advantage of the fact that fumaric acid is over 2.5x more soluble in ethanol.

Using the solutions described here allowed for rapid recovery of salts (ie 2.3g fully dried within 2 hours), and increased yields (almost 8g of additional salts were recovered from old solutions using FASA alone). Towards the end I describe some of the tricomponent solutions I made which work by modifying the volume and surface area of the dispersed droplets, and the results are definitely worth looking into. I have some great pictures too that are unique and interesting.

I posted this both to provide information that I was previously unable to find anywhere myself before conducting these experiments, and in addition I hope this can provide insight into further refinement and development of the process of fumarate salt precipitation.

From the Table of Contents:
I. Introduction
II. Molecular Sieves
A. Using Sieves Properly
B. Issues of Contamination
III. Alternatives to F.A.S.A.
A. Breaking Away from FASA Completely
B. Is Water Actually Ok to Use for Making DMT Fumarate Salts?
IV. F.A.S.W.
A. Limitations to FASW in Practice: Generation of Persistent Suspensions
B. Dealing With Suspensions, Method 1: Salting Out with Inorganic Salts
C. Dealing With Suspensions, Method 2: Salting Out with F.A.S.E.
V. Solubility Study
A. Quantification of Saturation Levels: Results
VI. F.A.S.E.
A. Advantage 1: Increased Solubilization of Fumaric Acid
B. Advantage 2: Enhanced Reaction Rates --> Quick Salt Recovery Times
C. Advantage 3: Ease of Salt Collection
D. Advantage 4: Increased Yields
E. Interesting Note #1: DMT Fumarate Salts from FASE have Altered Crystal Habits and Morphologies
F. Interesting Note #2: Freebases Converted out of Alternative Solutions May Also Exhbit Altered Morphologies
G. Interesting Note #3: Not All of the Dried Salts Were Re-soluble in Water
VII. Optimization of Salting Process Through Enhanced F.A.S.E. Solutions
A. The Yin and Yang of FASE and FASW: Advanced Salting Control
B. Multisolvent Systems and Dispersivity: Theory of Operation
VIII. Conclusions

I hope this proves useful.

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#2 Posted : 11/19/2019 6:57:57 PM

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Wonderful contribution my friend-- thank you so much for sharing this interesting and useful information!

Thumbs up
#3 Posted : 11/19/2019 9:20:38 PM

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Hey, thanks coAsTal! I was really hoping others would find it as useful and helpful as I tried to make, so that's great to hear.

Yeah.. Very happy
#4 Posted : 11/20/2019 8:21:40 AM

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Very nice work, thanks!

Quite hopeful that people still try to optimise the approaches, the FASA method is possibly over 10 years old now.

Samvidbuho wrote:

A. Breaking Away from FASA Completely

I am all up for moving forward!

Need to calculate between salts and freebases? Click here!
Need to calculate freebase or salt percentage at a given pH? Click here!

#5 Posted : 2/17/2020 7:50:40 PM

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Samvidbuho wrote:

II. Molecular Sieves
A. Using Sieves Properly
B. Issues of Contamination

Hey, thanks a lot for your work!

On the yellow-colored contamination of acetone over molecular sieves: it is NOT recommended to use molecular sieves to dry acetone, as they are slightly basic and promote self-condensation of acetone at warm temperatures, contaminating it and actually increasing its water content after a while. Take a look here, you can easily find more articles on this subject.

I recommend either drying acetone using anhydrous CaSO4 (aka "Drierite", large mesh is easier to filter off compared to powder) which is pH-neutral ( see "Purification of laboratory chemicals" ) - or, better yet, moving away from acetone and using IPA instead. Unlike acetone, you can wear nitrile gloves with IPA, its vapors do not destroy plastic lids, it does not self-condense, and the IPA molecule is large enough to use 4A molecular sieves (instead of 3A) to remove not just water (sub-3A) but a few other contaminants as well. In any case, it is good to drop a bit of your solvent onto some CuSO4 to quickly test the water content. Depending on where you live it may be possible to simply purchase anhydrous 99.9+% reagent-grade IPA and, assuming you can keep it air-tight at all times, skip drying altogether.

Some drawbacks of IPA are its higher toxicity compared to acetone and ethanol, extreme hygroscopicity (it sucks water out of air towards the 65% IPA - 35% water equilibrium) and somewhat higher solubility of DMT fumarate in room temperature IPA compared to acetone (but still lower solubility compared to ethanol).
#6 Posted : 2/20/2020 6:15:07 PM

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Great stuff, thanks Sam!

Here's the document again, attached in pdf format.
Ora, lege, lege, lege, relege et labora

“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli
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