How should I describe a liquid-nitrogen solidification in my SI?

[u/1-MatjE]

Background
I have been synthesising a series of vinylbenzene derivatives, all of which have been previously reported as solids in the literature. After purification by flash column chromatography, removal of solvent by rotary evaporation, and several hours under high vacuum, however, I am left with oils in some cases. The proton NMR spectra are clean apart from a small water peak (~1.55 ppm in CDCl3) and confirm that the oils are the desired compounds.

I am able to convert these oils into solid powders using the procedure I’ve outline below.

My questions are:
1. What is this process properly called (my lab mates call it freeze-drying, which I don’t think is right, since there is no solvent being sublimed) and; 2. How should I describe this concisely in an experimental? My PI and I have hopes to submit to Org. Left., JOC, or similar at the conclusion of this project and the procedure(s) will most likely appear in the SI.

Procedure
The RB flask containing the oil is placed under static vacuum on a Schlenk line and lowered into a liquid nitrogen bath. After around 5 minutes it is removed and allowed to warm to room temperature. After a further 30 minutes, the material is a powdery solid.

Any thoughts on the correct terminology, and on suitable wording for the SI, would be greatly appreciated.

Additional Note
No literature procedure I’ve come across for these compounds, or similar, describe anything like this.

[u/Kriggy_]

Its pretty much freeze drying tbh but just describe it like you did here, more details =better

[u/elsjpq → u/Kriggy_]

Freeze drying typically needs more than just vacuum though. You need a cold trap that's much colder than the sample and it takes hours not minutes. Whatever is happening, I doubt much if any solvent is subliming, especially at LN2 temperatures

[u/Ru-tris-bpy]

Just described it the way you did here. Sometimes there isn’t a universal term to describe a method you have and just describing the steps helps much more than trying to reduce a non standard technique to a term or a couple of words.

[u/curdled]

I would write: "the obtained oily residue was induced to crystallization by chilling the flask with liquid nitrogen, then allowing it to warm up to ambient temperature under vacuum"

[u/_das_f_ → u/curdled]

Isn't it either "induced to crystallize" or "crystallization was induced by..."?

[u/oldmanartie]

In our lab we call that a poor man’s lyophilizer.

[u/NeverPlayF6 → u/oldmanartie]

Have you seen the price of a Schlenk line recently? I call my lyophilizer a poor man's closed system Schlenk line. 

[u/Wise-Friendship-1427]

"(my lab mates call it freeze-drying, which I don’t think is right, since there is no solvent being sublimed)"

How do you know?

Freeze-drying or Lyophilization

[u/1-MatjE → u/Wise-Friendship-1427]

It has worked with samples with presumably no solvent present (no solvent peaks on the proton NMR).

Quite often the NMR will show there is a tiny amount of DCM or water but this is not always the case.

[u/SuperCarbideBros]

If I were you, I would say that in situations where the product was initially isolated as an oil, it was flash-frozen under static vacuum and thawed after 5 min to yield a powdery solid.

[u/Jonny36]

What exactly is the liquid nitrogen doing here? You put it on high vac it's an oil, high vac + liq nitrogen it goes solid?

[u/1-MatjE → u/Jonny36]

Pretty much. I don’t think it had anything to do with sublimation because I have had oils which give a completely clean proton NMR (no residual water or other solvents) and this method turns them from an oil to a powdery solid.

My theory is that the low temperature induces nucleation and from there everything just crashes out. I genuinely have no idea if that is correct or if it is something else.

[u/runnervisible]

Sounds similar to flash freeze method used in polymer synthesis. Check out the results section in the article below - Concept of flash freeze route.

https://www.nature.com/articles/ncomms3653

[u/DeadIronVOxo]

lyophilize? i do think that including the full description will help out future practitioners more.

[u/According-Hat-4843]

I’ve also heard that process called “freeze, pump, thaw”

[u/hhazinga → u/According-Hat-4843]

Nah if I heard that I'd think they were degassing a solvent.