[dziwnytyp]

Hi, I started crystallography this semester and I got problem. I have a teorethical question to answer.

I have to write(exactly step by step) how I would crystalize monocrystal of certain substances. And one of substances that I have to write about is organic liquid, which does not crystalize in standard conditions(f.e. CH₂Cl₂) and I got no idea how to start this. Books refer only to substances that can be crystallized in standard conditions, and they describe techniques such as solvent evaporation, slow cooling of the solution, solvent/ non-solvent diffusion, vapour diffusion and so on.


But how I'm supposed to crystallize liquid? What conditions(temp, pressure, etc?) and what technique and equipment? I got no idea how to start.

[Borek]

If it is not a solid at STP, it can't be crystallized at STP. So you need to tweak conditions, no other way.

[dziwnytyp]

If it is not a solid at STP, it can't be crystallized at STP. So you need to tweak conditions, no other way.

Is it possible to find out what should be conditions(I got to be specific, f.e. I have to write exact temperature, pressure etc), if I cannot find any publication about it?

[Arkcon]

Well, is your general example of dichloromethane actually the specific example you want to (have to?) use?  You want to crystallize that particular organic solvent, so you're wondering what pressure conditions to use.  Try another liquid, say, water.  How would you go about crystallizing water?  You've seen crystalline water before, right?

[dziwnytyp]

Well, is your general example of dichloromethane actually the specific example you want to (have to?) use?  You want to crystallize that particular organic solvent, so you're wondering what pressure conditions to use.  Try another liquid, say, water.  How would you go about crystallizing water?  You've seen crystalline water before, right?

Dichloromethane is only example, I have to describe crystalization of phenethylamine, which is organic liquid as well. It does crystalize as salt with HCl or HBr but I'm supposed to describe crystalized 'clear' PEA, and I should get big(1 kg ) monocrystal. I know, this task is stupid, but...

So the point I get here - I should reduce temperature, and increase pressure. I found an publication where they crystallized mentioned dichloromethane. The pressure they used was 1.6 GPa. I guess for PEA it should be similar.

[manofohm]

Interesting factoid: some liquids at roomtemperature take a deal of time to form a solid substance or crystals in general. basically when the amorphous becomes aligned.

Now I dont know if Phenylethylamine can handle these condintions but if it can form a solid at room temperature I have a method I my self designed that works great on amine based organic chemicals. This will not work to make a 1 kg crystal but i think some would be suprised the size of crystals that can be obtained.

Start with the HCl salt of the amine then add this to an amount of water that just completely dissolves this at room temperature. now add to a new tube (the thiner and taller the better) a slight excess of NaOH crystals or prills to the bottom and add your HCl salt solution down the side of the tube as slowly and carfully as possible as to avoid disturbing the now crystalizing free amine. Emphasis on not creating turbidity in the solution. Now leave this out at room temperature for a while for small amounts it may only take a couple hours. For larger amounts you will get much larger crystals but it can take forever it all depends. Add the now lengthy crystals to the fridge to get the stuff that dissolved in water out and continue on to removing filtering etc...

My theory in how this works is that when you first add this solution to the NaOH it creates a barrier in which the NaOH has to pass through and as your crystals grow the membrane you have now created gets longer and tighter so the NaOH becomes less and less available allowing a slower crystalization leading to much larger crystals.

I remember before thought this up I was trying to work with solvent systems that were different for every amine compound I was working with. And so many times precipitated white dust that could just fall through the filter paper and into the mother liquor as a white cloud of failure. NO LONGER! Take my word for it this method is boss.

[AWK]

Some compound can be crystallized in refrigerarors (we have in lab such machine with temperature down to -80 C). Next is relatively cheap liquid nitrogen or liquid helium. The serious problem is a mounting of such crystal for X-RAY.