zephler1
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nitroaldol not dehydrating to nitrostyrene or something else?
I read a report about some researchers trying to make a nitrostyrene. They used 10g of the aldehyde, added an equivalent of nitromethane and 50 mL of
methanol. They chilled this to 0C. Next they prepared a KOH\Water\Methanol mixture (1:1:2) chilled this to 0C and added 20 mL of it to the chilled
aldehyde \nitromethane\alcohol mixture dropwise with good stirring. An orange solution resulted. This was stirred for 10 minutes, and then added to
50 mL of conc HCl which was also at 0C. This caused a large amount of canary yellow precipitate to fall out, almost stopping the stirrer - some water
was added to help mixing. The precipitate was washed with water. When measuring it's melting point however, it came out to be at least 10C higher
than the literature nitrostyrene. I wonder, is it the nitroaldol still? Does HCl do a good job of dehydrating nitroaldols? Is this some kind of
nitronate salt? Should H2SO4 have been used instead? Does anyone with experience in this type of nitrostyrene formation have a notion of what has
happened?
[Edited on 18-7-2014 by zephler1]
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Nicodem
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Thread Moved
19-7-2014 at 01:56 |
kmno4
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"nitroaldol" - what it is, some mysterious nitroaldehydealcohol ?
Your "researchers" should have read OS paper (DOI:10.15227/orgsyn.009.0066) about preparation of β-nitrostyrene. Recently I have prepared about 10
samples of mentioned compound (from 3g of benzaldehyde each), with slight modifications in each synthesis. It is because I could not gain declared
yield of β-nitrostyrene, given in OS paper.
But the rest went exactly like in the procedure.
However, I am not sure what you mean by "a nitrostyrene" and "aldehyde".
Слава Україні !
Героям слава !
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Chemosynthesis
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At least there's no "SWIM."
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FireLion3
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More often than not melting points can vary by a few degrees depending on impurities in the product, but without knowing your specific product, it is
impossible to tell you if it dehydrated or not. If this aldol product has an aromatic ring, especially an electron rich one, dehydration usually
occurs readily at a low temperature due to delocalized electron resonance and conjugation of the side chain with the aromatic ring.
The addition of the HCl in this particular prep is not to dehydrate it, but to neutralize the KOH. Acid catalyzed dehydrations usually require
heating. There is really not much way the HCl would have dehydrated it because it would neutralize against the KOH instantly. The KOH on the other
hand would dehydrate it. If the compound is electron rich, such has having methoxy/ethoxy/methyl/benzodioxole ring on it, then dehydration is even
more favored, because the molecule would be conjugated between the ring and the nitro group, and the nitroalkene is more substituted.
By the way
Your prep has a striking amount of similarities to this one:
https://www.erowid.org/archive/rhodium/chemistry/mdp2np.html...
You even used the phrase verbatim "canary yellow". The temperature is kept low in the above prep because the target compound is so electron rich that
in the presence of bases or acids it can easily polymerize. It is even more electron rich than its ketone cousin, being even more prone to these messy
polymerization. With that said, this particular compound dehydrates almost instantly in the presence of a base because of its electron richness.
Incomplete yields or imprecise melting points caused by impurities would be from incomplete condensation or the presence of polymerization products,
or both. Because of the conjugated structure of this molecule, it is very prone to polymerization.
Just so you are aware, there's nothing wrong with discussing or trying drug preparations. Illicit drugs and their precursors are not illicit
everywhere in the world, and many of these so called precursors have an infinite amount of uses outside of their illicit drug association. Plenty of
people work in licensed research labs with permission to synthesize these types of chemicals and often frequent this forum. Nobody here is going to
demand you fork over your govt issued-license or prove that you are in a country where they are legal, but if you post suspiciously, nearly word for
word from known drug preps, and disguise the fact, then you are going to get a lot of scrutiny. There are a couple of places in the world were the
above compound is perfectly legal to synthesize - not everyone lives in the USA.
Just keep to the chemistry and try not to make it seem like you are trying to hide something. Many of us have jobs and do not want to
be accidental accomplices to felony behavior. It's your business what you do. But there is absolutely no sense in going out of your way to make
yourself appear suspicious. There is in fact hundreds of legitimate and very effective uses for so many known "drug precursors", and many of us law
abiding experimental chemistry enthusiasts have to suffer and be restricted from accessing these things because of nefarious drug users.
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Crowfjord
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According to the orgsyn.org entry for beta-nitrostyrene (Org. Synth. 1929, 9, 66. DOI 10.15227/orgsyn.009.0066) adding the sodium salt of the nitro
alcohol both neutralizes and dehydrates said molecule. "The alkaline solution must be added slowly to the acid, for reverse procedure always forms an
oil containing a saturated nitro alcohol. A large excess of acid at room temperature is used, conditions which facilitate the formation of the desired
unsaturated nitro compound. I.e., if one wanted the alcohol instead, they could neutralize without dehydrating by adding dilute acid to the basic
solution.
Of course, the above comments about temperature are true - room temperature is fine for the unsubstituted compound, but electron-rich compounds should
be treated at lower temperatures.
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