P2NP by Knoevenagel Ultrasound writeup/questions

joe_aldehyde · huxleys associate

procedure was as follows:

10,6g benzaldehyde food grade
7,5g nitroethane
16,2g nh4OAc
6g CH3COOH glacial

sonicated it for about 4 hours in a 250w ultrasound bath (professional one with 2 knobs to change the intensity and frequency, intuitively adjusted them to make the surface of the liquid inside the stoppered erlenmeyer flask sitting in the bath undulate nicely). it took quite a while for the ammonium acetate to dissolve, about 2 hrs. maybe. a dark orange layer formed on the bottom, while the upper layer was of a butter-like yellow color. separated the 2 layers, the orange one was about 17ml and has a nauseating smell (this stuff makes me sick if i get to smell it for too long, even though it stands in a fume hood! is this characteristic for p2np?)

the orange layer was set aside in the freezer, but even after a few days it only became thicker, no apparent crystallization of the suspected nitrostyrene. the viscosity might have changed due to water becoming ice.
i got a few small crystals (probably less than 1mg) after i tried to extract the other (HOAc) layer with 1,2-dichloroethane (bad choice...carcinogenic shit! it just stood there beneath the fume hood, so i used it). after evaporating the solvent, the orange colour deepened a bit - i just heated the stuff at about 130 deg.C to evaporate water, solvent, nitroethane. after that, the orange mass got quite thick but still stirrable. in the freezer, only a few tiny crystals formed.
i also noticed that upon contact with acid, the p2np seems to polymerize or do some other weird shit - it becomes a pale blue solution.

now the question is: how to get a product that is pure enough for some tries at reduction? i've read at lot about recrystallization of the p2np but i still got a liquid, do i need to vac distill it first?
for recrystallization i got acetone, toluene, DCM, EtOH, MeOH, a bit of iPrOH, cyclohexane, chloroform.

please do also suggest some reduction methods you want me to try. i have thought of NaBH4 followed by Zn/HCOOH or Zn/HCl. also a CTH using HCOOH (does Calcium Formiate work well as a hydrogen donor, too?) would be possible. i also have quite a bit of 10% Pd/C from Degussa which i would like to use in a catalytic hydrogenation with molecular H2 generated by dissolving metal in mineral acid or NaOH). if i get some overhead stirring equipment, i would also try urushibara. or urushibara in the ultrasound bath? post away, bees!

cheers,
j_a

joe_aldehyde · huxleys associate

ok, today i put all the stuff in the rotavap with aspirator vacuum attached. got rid of almost all acetic acid, i left the rest as it might have taken too long. the other part of p2np changed its viscosity pretty much, it is now a sticky deep red-orange oil. a few tiny crystals seem to have formed (opaque mass), but no signs of bigger crystals yet.
the third part of p2np was also rotavapped, surprisingly it changed its color, this part is now a very deep orange-red. i suspect it might have decomposed a bit - how heat-sensitive is p2np? i only used a water bath, so temps never got anywhere beyond 100deg.C

how do i get this stuff to crystallize? or is there any other way to purify it? i could vac distill it, but i tried that before without success - bp. must be too high.

icecool · Insistent Chemist

The boiling point is around 65*C....
So I guess you melted the crystals especially under vacuum...
You shouldn't do this at all in a rotavapor.
But just reflux it (nitroethane and benzaldehyde with R-NH2) and then put it in the freezer.

joe_aldehyde · huxleys associate

well i thought the mp. was around 65-70 deg.C! the bp. cannot be that low, otherwise it would have boiled off in the rotavap.

how do you do your usual workup? i put the post reaction mix in the freezer, never got crystals. i did the 3rd batch last night. and i don't like the reflux method because ultrasound works so beautifully Smile

IndoleAmine · Dreamreader Deluxe

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IndoleAmine · Dreamreader Deluxe

I doubt he can. But what do I know, hehe.

Your temp. suggestment of 50-60°C is surely meant the nice way - but can you give further evidence? Because during recrystallization, boiling in 80°C hot alcohol doesn't matter, as well as it doesn't when you use n-butylamine/toluene/dean-stark-trap... Rolling Eyes

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IndoleAmine · Dreamreader Deluxe

Personal experience is generally considered worth shit around here, sometimes. Wink

Thus I can even provide refs where p2np is reXtalized from IPA several times, with no more losses than in another ref I have, where the'yre reXtalizing from MeOH....

If you desire so....

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IndoleAmine · Dreamreader Deluxe

A rotovap at aspirator vacuum should be well capable of removing all solvents that were mentioned here so far, without the need of more than 50-60°C bath temp (this even applies to toluene which is the highest-boiling of the mentioned compounds).

p2np doesn't care if solvent is present or not if it is about to polymerize, I would say. Some "solvents" also simply act as stabilizers (or are there to contain them), btw....
(rather than creating space between molecules)

And with n-BuNH2/dean-stark and toluene solvent at reflux, the product crystallizes in superior quality directly from the rxn mixture upon cooling, so I would say toluene is excellent for this specific substrate. Haven't yet tried EtOAc though.

And just btw, butylamine is also excellent for 3,4,5-trimethoxynitrostyrene synthesis, provided excess GAA solvent is used (anywhere from 98-100% GAA will do fine IME)...

(one reXtalization and ready to go - in contrast to the ugly red shit you often get when using (methyl-)ammoniumacetate on this substrate (which seems to be very prone to polymerization in general)).

But what do I know.

i_a

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Electroencephalopod · Sat Jun 25, 2005 1:13 pm

OK, I posted a fairly noobish question about the use of ultrasound in increasing yield from a plant extraction. Now this makes the Pod feel a little more noobish. Thank ye kindly for the post in retrospect, Sir Joe.