10-16-01 21:37
No 225364
What's the function of the ammonium acetate in forming 2,5-DMNS from 2,5-DMB? Are there any substitutes?
Also, going from 2C-H to 2C-B, is there a way that avoids elemental bromine and uses, say, sodium bromide/oxidizer?
(Chief Bee)
10-16-01 21:46
No 225368
The ammonium acetate acts as a base, and is a catalyst for the reaction. There are numerous substitutes if you browse similar syntheses in Pihkal. The best substitute I've seen is ethylenediammonium diacetate, which opens up for 95%+ yields: ../rhodium /edda.ht
Other halogenation methods are abundant: ../rhodium /2cb.bea
(Hive Addict)
10-16-01 23:25
No 225406
The 2C-H*HCl was dissolved in a 300 mL H20. The pH was adjusted to >12 with 20% NaOH and the aqueous layer was extracted with 4x100 mL DCM. The DCM was evaporated to give 2C-H freebase, which was dissolved in 500 mL of 3:1 AcOH/H2O. The rxn was cooled to 0C in an ice/water bath. 37.3g of 48% aq. HBr was added, followed immediately by 23.8g of 30% H2O2.
Instead of using 215mmol (17.4g) HBr in the above example (ie 37.3g of48% aq HBr), could one just use 22.1g (215mmol) NaBr?
Also, will other weak bases, like NaHCO3 work as a Henry reaction catalyst?
(Chief Bee)
10-16-01 23:44
No 225411
In that case, use 215 mmol NaBr and 215 mmol H2SO4, otherwise hypobromite will be formed and not HBr. I don't think AcOH is strong enough to turn NaBr into HBr.
(Stoni's sexual toy)
10-17-01 00:53
No 225432
You definitely need a strong acid.
Also, adding the H2O2 slowly might give you better results, since this way no excess H2O2 will be present.
And a little excess HBr/Br2 won't hurt yields either.
Since the freebase will eat up an equimolar amount of acid I wouldn't bother with preparing the freebase for this bromination step anyway, just use the hydrochloride, it will work just the same.
I have seen all kinds of amines being used in nitrostyrene preparation (e.g. MeNH2, cyclohexylamine, butylamine, ethylenediamine etc), but yields might differ widely.
(Hive Addict)
10-17-01 00:59
No 225434
Rhod, fair enough. From what I understood the HBr/H2O2 was used to generate in situ bromine, which I think NaBr/H2O2 in HOAc could do as well.
Also, from what I understand, the Henry reaction is just a special case of an Aldol reaction (a so-called nitro-aldol reaction). So it looks like strong bases, such as NaOH would be able to catalyse the reaction. Unfortunately it seems nitromethane is incompatable with NaOH, which is why ammonium acetate is used. Any ideas about using NaHCO3?
(Chief Bee)
10-17-01 01:07
No 225435
NaOH can be used, at least in some instances: ../rhodium /mdp2np.
(Stoni's sexual toy)
10-17-01 01:09
No 225437
> From what I understood the HBr/H2O2 was used to generate
> in situ bromine,
Exactly.
> which I think NaBr/H2O2 in HOAc could do as well.
I tried it by reacting NaBr, AcOH and 30% H2O2. No reaction was visible, no colour change. When ~30% battery acid was added bromine was produced instantly.
The reason why H2O2 should be added slowly IMHO is the following:
2x HBr will produce Br2, which brominates the aromatic nucleus forming another molecule of HBr, which then has to be re-oxidised into Br2. By adding all the H2O2 at once, you will (right at the beginning of the reaction) have only half the required amount of Br2 for complete halogenation present and half of the H2O2 will be left over unreacted waiting for more HBr to show up. This excess H2O2 might do bad things to your stuff, or over-oxidise the Br2, or partly decompose. All side reactions which will potentially lower your yield.
If you wanted to add all the H2O2 at once I'd use at least two moles of NaBr per mole of amine plus the same amount of a strong inorganic acid, to ensure complete conversion of the bromide into Br2 and limit side reactions.
Never heard of NaHCO3 being successfully used in nitrostyrene preparation. I guess it will be pretty insoluble in the nitroalkane, and therefore might not react.
Do some microscale test to find out if it will work, but I'd rather use one of the proven catalysts here.
(Hive Addict)
10-17-01 01:12
No 225438
Os, ok... from Dal Cason's MDA review I noticed that 3,4-methylenedioxy-2-nitropropene could be made from nitroethane and piperonal using any of the following catalysts:
A) ammonium acetate
B) sodium hydroxide
C) methylamine
D) pentylamine
E) butylamine
F) ethyldiamine
G) ethylamine
I assume the same catalysts can be applied to nitromethane condensations with benzaldehydes...
But from MSDS I've read on nitroethane (and nitromethane) it seems like it's a bad idea to combine nitro(m)ethane and strong bases... what's up with that? I could easily give benzaldehyde and nitromethane with sodium hydroxide a test round here. Is my nitrosytrene going to be a colored crystal? Forgive my ignorance to all this, I'm very new to this ground.
(Hive Addict)
10-17-01 01:17
No 225441
AWESOME! Thanx Rhodium, that's exactly what I'm looking for. I really should read thru all the nitrostyrene/nitropropene material on your website...
(Stoni's sexual toy)
10-17-01 01:21
No 225442
> But from MSDS I've read on nitroethane (and nitromethane)
> it seems like it's a bad idea to combine nitro(m)ethane
> and strong bases... what's up with that?
They will produce an explosive compound. Nitromethane sensitized by bases is a strong explosive, and the sodium salt will be insoluble in the nitromethane. But as long as you stick to the procedures and don't try to isolate the sodium salt nothing bad will happen.
> Is my nitrosytrene going to be a colored crystal?
Yes.
> Forgive my ignorance to all this, I'm very new to this
> ground.
Check Pihkal to get a general idea about nitrostyrene properties, lots of nitrostyrenes and propenes mentioned in there.
(Hive Addict)
10-17-01 01:31
No 225444
So you're saying if I use ../rhodium /mdp2np.
(Hive Bee)
10-17-01 02:07
No 225456
Experimental data suggest these condensation reactions occur more quickly when using cyclohexylamine as a catalyst than n-BuNH2.
I didn't know NaOH could bee used... that's very interesting indeed
.Sweet dreamz,
IudexK
(Chief Bee)
10-17-01 02:16
No 225459
No, the worst thing that could happen would be low or no yield (I don't know how general the reaction is).
(Hive Addict)
10-17-01 03:50
No 225503
<HUGS>
Thanx guys, you made my day. I hope the yields are good, I will hopefully have some reports in a couple weeks.
ps. it seems that there's little benzaldehyde in almond extract (as sold at the grocery store). I tried distilling some, and all I got was an alcohol/water/benzaldehyde fraction (90-130C) and a propylene glycol fraction (188). Yes, I used a column, yes, I went slowly.