recrystallization of P2NP, issues...

joe_aldehyde · huxleys associate

can someone point out how to correctly recrystallize P2NP?
usually, one adds as much solvent as is needed to fully dissolve the substrate so upon cooling, crystallization sets in with a supernatant of solvent which holds the impurities - so far for the ideal case.
p2np seems to be all too soluble in IPA, from which it is usually recrystallized. in all attempts of swija however, when crystallization set in, there is no supernatant but a big lump of yellow p2np with all the IPA in between the crystals, no chance to filter off the solvent. whats going wrong here?

Bushroot · Thu Aug 25, 2005 8:38 pm

do you filter it by suction? It's impossible to make dry crystals if you use gravity filtration...

What I do to recrystallize my P2NP -
Heat some IPA to boiling (2x amount of P2NP just in case, use even less)
Put the glass with P2NP on a heating plate and slowly add IPA with good mixing.
If the solution is concentrated (not too much IPA I mean!) the P2NP will start forming it's long needles as soon the boiling stops.
I put the solution into the fridge, and then filter off the crystals on Buchner funnel.
Repeat cooling filtering to get a second crop.
If you want to get all that P2NP out you may add some water to make IPA cloudy. All the crystals will immidiatelly fall out...

joe_aldehyde · huxleys associate

yes i do filter by suction. from what i can see i'd say i have a pretty much oversaturated solution of P2NP in IPA, which i could take off the hotplate and pour it into a plastic container for crystallization (which commenced after some minutes, but there were no long needles - mostly yellow tiny needles).
you see, my problem isn't that there are no needles, with the amounts of IPA i use, there is just no IPA left to filter off, it seems to be trapped in the crystalline mass.

what about using another solvent? swija has pretty much everything at hand. it seems to me that P2NP is pretty soluble in IPA, right?

hAzzBEEn · Fri Aug 26, 2005 5:57 am

This is really basic, so don't be offended. Is SWIy covering the container when cooling to make sure the solvent doesn't evaporate? Also, have SWIy tried breaking up the mass a little bit to free up the remaining alcohol?

joe_aldehyde · huxleys associate

well in the second attempt, the container wasn't covered. it can't have been much solvent that evaporated, though. in swijas lab practice, NEVER were coverings used upon recrystallization due to the fact that at the boiling point of the solvent, there should already be some crystals precipitating, which is not the case due to oversaturation of the nitropropene/IPA solution.

swija did also try breaking up the mass upon crystallization, which did no good.

Bushroot · Fri Aug 26, 2005 2:34 pm

P2NP is soluble in all alcohols, so it can be recrystallized from unhydrous ethanol, n-propanol and butanol. But IPA is optimal for this procedure. At room temp P2NP is almost insoluble in the listed above.
Maybe you should filter the mass in small portions, the solvent can't be trapped in crystals. But the filter can be plugged by P2NP and do not allow the liquid to come through... I use common coffee filter and crystals become almost dry within 2-3 minutes.
If you don't get needles means your product is not very pure, or the alcohol contained some water.

joe_aldehyde · huxleys associate

i do get big needles in the middle of the mass, and small needles towards the edges of the container. my filer is all right, it's a sinter glass funnel. even if i filter in small portions, no IPA comes through...and i didn't say the IPA is trapped inside the crystals, but in between the crystalline mass which has spaces Smile

Bushroot · Sat Aug 27, 2005 3:24 pm