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Author: Subject: Reductions of Nitro groups with Zn and acid
xwinorb
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[*] posted on 31-10-2008 at 14:58


To Isomeric_Fred :

I never got less than 55 % with the modified Leminger method. I never tried exactly the procedure as in the Rhodium page ( Leminger paper ). Can tell you it works very well for the 2,5-DMBA, my latest was 75 %. If interested see my previous posts.

It DOES NOT works so well for 3,4,5-TMBA though, yields much lower. I would suggest acidic Al-Hg for this one.

I usually use batch sizes 20 g or so of the 2,5-DMBA, in a 2 l BF.

xw.
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stoichiometric_steve
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[*] posted on 1-11-2008 at 04:20


Something else that seems to be critical for a nice yield: keep the reaction hot and don't add the HCl too slowly, otherwise the Nitroso intermediate will tautomerize to the Oxime and hydrolyze to the parent Carbonyl compound.



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stoichiometric_steve
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[*] posted on 23-9-2020 at 13:58


Quote: Originally posted by Barium  
I know of several members of the Hive who have successfully used my methods. Both well trained chemists and simple cooks.


If you ever come back to read this:

Fuck you, Thomas Lillius
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njl
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[*] posted on 23-9-2020 at 17:51


Yet another rollercoaster of a thread. Steve, what prep are you referring to in that 11/1/08 reply? I've been try a few variations on the SM thread linked in the rhodium archive where HCl is added to the substrate in methanol, with zinc being added afterwards and the reaction being cooled.
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stoichiometric_steve
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[*] posted on 24-9-2020 at 01:30


Referring to the reduction of secondary nitro compounds with Zn/HCl.

You meant the Leminger variant, which is preferable for primary nitrostyrenes.

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njl
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[*] posted on 24-9-2020 at 02:18


Right. Honestly the procedure calling for zinc held in suspension with the substrate and addition of the acid over time was much more convenient when I tried it on nitrostyrenes and I did end up getting reasonable yields despite screwing up isolation. What about the kinetics makes the order of addition more favorable for different substrates?
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OrganicGuy
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[*] posted on 20-12-2020 at 05:07


Quote: Originally posted by stoichiometric_steve  
Yeah, i was wrong about the figures. Whatever those indians claimed, i don't believe them.

The Fe/HCl reduction (yielding ketones) works best at 100°C and 7:2:1 Fe:HCl:Nitroalkene, solvent water, vigorous stirring, and a dash of FeCl3.

Quote:
Originally posted by Barium
What do you mean? Am I omitting details or what?


I'm not sure what's wrong with some of your procedures, it could just as well be my fault. But as for your "really wet redfuctive amination", i know of several people (who have the right kind of experience) having been unable to reproduce your claimed yields. The best i got myself was 10%.

Quote:
Originally posted by Barium
Seeing you talking about dimeric products and silica gel makes me believe you are talking about the borohydride/EtOH/Dioxane reduction system


Nope, i do know my shit. The dimerization is also a problem here - Especially when making indoles the way these fellas did: Beer et al., J. Chem. Soc.; 1948, 1605-1609

BTW Barium, you probably never noticed how useful your water/toluene/PTC system is for reduction of secondary nitroalkenes. Your writeups and posts left me with the impression that all you wanted is to avoid PTCs, despite the fact that there is no double bond reduction as simple as this. I applied it to large scale batches and it is the best method - easy workup, reaction runs on its own, great yields, easily recycled solvent.


Bets results I had was with 5:2:1 if carbonyl iron powder, but with regular cheap 99% iron powder then I had best results with 12:2:1 eq of Iron/Hcl/p2np.
But best of all works 5:2:1 with zinc/acetic acid 98%/p2np. Reaction time only 30-40 min
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Corrosive Joeseph
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[*] posted on 20-12-2020 at 05:20


Quote: Originally posted by OrganicGuy  

Bets results...


Hey OG, you got any actual yields for that.....?



/CJ




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[*] posted on 20-12-2020 at 05:35


Zn/HCl aint so bad to extract if you just add a large excess of hydroxide to re-dissolve the zinc.
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stoichiometric_steve
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[*] posted on 20-12-2020 at 10:59


Quote: Originally posted by OrganicGuy  

But best of all works 5:2:1 with zinc/acetic acid 98%/p2np. Reaction time only 30-40 min


I'd like to know the exact conditions for this procedure, would you be so kind to share them?
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[*] posted on 2-1-2021 at 09:05


Quote: Originally posted by stoichiometric_steve  
Quote: Originally posted by OrganicGuy  

But best of all works 5:2:1 with zinc/acetic acid 98%/p2np. Reaction time only 30-40 min


I'd like to know the exact conditions for this procedure, would you be so kind to share them?

yes I can do it in a week when I'm home at my computer, but check this doc. I've seen you had a lot of good posts here & there, so you'll figure it out yourself by then ;)


Attachment: AUS amphetamine.pdf (1.9MB)
This file has been downloaded 203 times

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stoichiometric_steve
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[*] posted on 2-1-2021 at 22:44


You probably misread that document. There is no mention whatsoever of any yield that high.
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[*] posted on 3-1-2021 at 07:48


Quote: Originally posted by stoichiometric_steve  
You probably misread that document. There is no mention whatsoever of any yield that high.

What yield?, I didn't mentioned how much yield I had, I only stated "the best yield I had was with..." and not how much
The percentage 98 and 99 is purity of iron and concentration of the acetic acid and has nothng to to with yields.
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[*] posted on 3-1-2021 at 07:56


Quote: Originally posted by stoichiometric_steve  
You probably misread that document. There is no mention whatsoever of any yield that high.

During the yrs I have also understood that because a certain document says so and so, doesn't mean you will have the same yield. I have seen many fake indian documents claiming excellent yields, but when running it exactly the same conditions I got half. And I have seen documents where I had better yield than they got after some experimentation. A document or journal is not static information, experimentation is always recommended
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stoichiometric_steve
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[*] posted on 3-1-2021 at 13:50


I stand corrected, i misread. I thought the 98% stood for yield. But the actual yield of the procedure is absolute shit.
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[*] posted on 3-1-2021 at 14:40


Interesting that a key here seems to be a fast addition and high temp. It seems more often "difficult" reactions call for exactly the opposite. Maybe the reason this rxn is so famously unreliable is that people optimize for the wrong thing.



[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 3-1-2021 at 23:09


If the reaction works ok, you can extract it with chloroform 1.49g/ml instead of toluene 0.865g/ml, which may form emulsion easier than chloroform would.



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[*] posted on 4-1-2021 at 06:56


Quote: Originally posted by stoichiometric_steve  
I stand corrected, i misread. I thought the 98% stood for yield. But the actual yield of the procedure is absolute shit.

If using the iron method, then the carbonyl and reduced/electrolytic iron powder gave yields better than regulare cheap iron powder (80-85%). For the zinc/GAA method, with electrolytic zinc powder I had 75-80% and with cheap zinc below 70%, however the short reaction time is preferable to me since I value family time. It also depends of course of the nitroalkene purity, AFAIK that's of highest concern when talking yields in these methods. Crap in crap out...

The most recent doc I had is this attached. It's indian though, but seems worth checking out. Good luck to you with the yield


Attachment: Fe_HCl_MeOH.pdf (435kB)
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stoichiometric_steve
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[*] posted on 4-1-2021 at 22:59


Quote: Originally posted by OrganicGuy  
Good luck to you with the yield


No worries my little dude, i had awesome yields with electrolytic iron powder.

750ml H2O
200g Fe
1 mol Nitroalkene
2.5g FeCl3
650ml HCl conc.
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