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stoichiometric_steve
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Reductions of Nitro groups with Zn and acid
Referring to the well-known procedures of Bandil and Barium, in response to some questions at the CTH thread:
In my experience, in Bariums (and Bandils) writeups it appears that everything is done in a flash. Trust me, it usually is not. Reductions
with Zn/acid are a pain to deal with unless you steam distill your product out of the mix. It IS possible to extract the basified rxn mix
with toluene, but you need a huge sep funnel and quite a bit of patience.
I do wish you good luck in getting NH4COOH to work with Zn. It didn't work for me, and i'd rather use HCOOH, CH3COOH or HCl.
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starman
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Well I did want to try ammonia formate,went to considerable trouble to synthesise.(we can't buy anything here)I haven't been able to produce formic
acid more concentrated than around 50%(by density via oxalic).So practically limited to formate salt of some description,but I do possess good
quantitites of reasonable purity zinc dust.
I know jack about CTH or reductions in general,The Zn/formate procedure I looked at didn't have A/B in the work up.So basically I would rather listen
while you guys talk and ask a question or two here and there for my education.
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stoichiometric_steve
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| Quote: | | Originally posted by starmanThe Zn/formate procedure I looked at didn't have A/B in the work up. |
If there also was no steam distillation, then it is pretty hard to get pure product from this procedure.
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Nicodem
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| Quote: | Originally posted by starman
Well I did want to try ammonia formate,went to considerable trouble to synthesise.(we can't buy anything here)I haven't been able to produce formic
acid more concentrated than around 50%(by density via oxalic).So practically limited to formate salt of some description,but I do possess good
quantitites of reasonable purity zinc dust. |
You went trough the trouble of preparing formic acid just to waste it in a reduction of a nitro compound with Zn powder? I hope you are aware that
even HCl with Zn works. In some cases even acetic acid. And you don't even need Zn - even tin, iron or amalgamated aluminium works.
| Quote: | | I know jack about CTH or reductions in general,The Zn/formate procedure I looked at didn't have A/B in the work up. |
The Zn/HCOOH and Zn/HCOONH4 are not CTH reductions and have nothing to do with CTH reductions using formates as hydrogen donors. The zinc powder is
consumed during the reaction, acting as the reducent, while HCOONH4 is just a weak acid necessary as a proton donor (not hydrogen donor as in CTH
based reductions).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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tapira1
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Fe - HCl reduction
Iron filings and a strong acid is able to reduce nitro groups such as nitrobenzene to amines like aniline.
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Klute
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aromatic nitro groups are much easier to reduce than aliphatic, and give cleaner products (less side reactions).
I suppsoe in theory Sn, Fe, etc could reduce aliphatic nitro groups, but I don't recall seeing any preparative procedures, except perhasp for the
lower chains: nitromethane, nitroethane, etc.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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merlic79
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Couldn't one just use Sodium Dithionite in a basic H20 MeOH media to reduce to an aniline? It is readily available at the Home Depot as a rust cleaner
in 1 pound containers for $6. However, it does contain a bit of bisulfite in it though.
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smuv
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Zn/HCl Reduction of Nitrostyrenes to phenylethylamines
Fe/HCl Reduction of Nitrostyrenes and nitroethanes
Synthetic Communications®, 35: 913-922, 2005
[Edited on 27-8-2008 by smuv]
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Klute
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My bad
The Zn reduction I knew about, but the Fe reduction gives the oximes (which are then hydrolyzed to ketones) IIRC. I suppose Sn gives similar results?
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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stoichiometric_steve
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Please note that this procedure doesnt really work as advertised. It says that it gives a 60% yield of mescaline from the nitrostyrene, while it has
been stated elsewhere that reduction of nitrostyrenes with acid and metal give predominantly the dimeric product. an addition of powdered Silica Gel
is needed to make this reaction work with nitrostyrenes (as opposed to nitropropenes, which give ketones and oximes).
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Nicodem
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Zinc with conc. HCl in a cosolvent like isopropanol reduces aliphatic nitro compounds. If kept at 0°C it reduces omega-nitrostyrenes to
2-phenylethylamines as well (however, it only works with terminal nitro alkenes). There are plenty examples posted in several forums confirming that
this method works as published once mastered.
Sodium dithionite only reduces nitroaromatic compounds. It does not work on aliphatic nitro compounds as far as I know (but I'm not sure). Though,
since it reduces conjugated double bonds, it might actually be useful in preparing nitroalkanes from conjugated nitroalkenes which can then be reduced
by other methods. Such a two step procedure could be higher yielding than a direct reduction of nitroalkenes to amines. However, I never saw
dithionite being used on nitroalkenes, just acrylates.
Iron powder might not work as advertised in that Synth. commun. paper on nitrostyrenes, but there are plenty of other published papers where Fe/AcOH,
Fe/HCl(aq)/cosolvent or Fe/NH4Cl/EtOH/H2O and even FeSO4/NH3(aq) is used to reduce nitroalkanes (both terminal and secondary nitroalkanes as well as
beta-nitroalcohols) to amines (just make a literature search and you will find plenty references). The same goes for Sn/HCl(aq)/cosolvent and
SnCl2/HCl(aq)/cosolvent combinations (SnCl2/HCl(aq)/MeOH does not reduce nitrostyrenes to amines, but the reduction stops at 2-aryl-2-methoxyetanal
oximes).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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starman
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| Quote: |
The Zn/HCOOH and Zn/HCOONH4 are not CTH reductions and have nothing to do with CTH reductions using formates as hydrogen donors. The zinc powder is
consumed during the reaction, acting as the reducent, while HCOONH4 is just a weak acid necessary as a proton donor (not hydrogen donor as in CTH
based reductions).
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Thanks for clearing that up.Saved me asking what is obviously a silly question.
| Quote: |
You went trough the trouble of preparing formic acid just to waste it in a reduction of a nitro compound with Zn powder?
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Ah well....it was a fun learning experience and have subsequently improved my azeotrope to circa 75%,hopefully anhydrous CuSO4 will dry to the mid
80's.
Thanks for the replies,I'll research the suggested references.
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Barium
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| Quote: | Originally posted by stoichiometric_steve
In my experience, in Bariums (and Bandils) writeups it appears that everything is done in a flash. Trust me, it usually is not. Reductions
with Zn/acid are a pain to deal with unless you steam distill your product out of the mix. |
What do you mean? Am I omitting details or what?
[Edited on 29-8-2008 by Barium]
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Barium
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| Quote: | Originally posted by stoichiometric_steve
Please note that this procedure doesnt really work as advertised. It says that it gives a 60% yield of mescaline from the nitrostyrene, while it has
been stated elsewhere that reduction of nitrostyrenes with acid and metal give predominantly the dimeric product. an addition of powdered Silica Gel
is needed to make this reaction work with nitrostyrenes (as opposed to nitropropenes, which give ketones and oximes). |
Does it really? I can't find the number 60% mentioned with mescaline in that article. What I can find, is that they claim to have reduced
3,4,5-trimethoxy-beta-nitrostyrene to mescaline in a 72% yield, and 1-(3,4,5-trimethoxyphenyl)-2-nitroethane to mescaline in a 75% yield. I can
believe the latter but I have a hard time believing the former.
Seeing you talking about dimeric products and silica gel makes me believe you are talking about the borohydride/EtOH/Dioxane reduction system to
reduce nitroalkenes to nitroalkanes and not any metal/acid system.
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stoichiometric_steve
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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
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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.
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Barium
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| Quote: | Originally posted by stoichiometric_steve
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.
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I'd use Fe/HCl and aqueous acetone or MEK at reflux, or even Fe/HCl in aqueous acetic acid at about 90 deg C. But that old patent works quite well
too.
| Quote: | Originally posted by stoichiometric_steve
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%.
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I report the yields I get. Why others have problems reproducing them can be due to a whole lot of reasons. It can be something as trivial as too low
stirring speed (especially in PTC-reactions), as well as wrong catalyst (like trying to use platinum instead of palladium) or the correct catalyst but
wrong support material (e.g. alumina instead of carbon).
| Quote: | Originally posted by stoichiometric_steve
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.
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I've modified that system a bit since the Hive went down. But yes, I know it is a clean method.
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stoichiometric_steve
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| Quote: | Originally posted by Barium
I've modified that system a bit since the Hive went down. But yes, I know it is a clean method. |
Please elaborate.
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Isomeric_Fred
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| Quote: | Originally posted by Barium
| Quote: | Originally posted by stoichiometric_steve
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%.
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I report the yields I get. Why others have problems reproducing them can be due to a whole lot of reasons. It can be something as trivial as too low
stirring speed (especially in PTC-reactions), as well as wrong catalyst (like trying to use platinum instead of palladium) or the correct catalyst but
wrong support material (e.g. alumina instead of carbon). |
I feel like a broken record, but really most of ur procedures dont work, especially when followed to the letter. Perhaps you omitted some important
side notes which you deem basic or something and we just dont figure it out? All I know is that the numerous times ive used your procedure ive failed
to get any meaningful yields. Except for some stuff like what stoichiometric steve said bout nabh4 reduction of nitroalkenes...
Back to the thread at hand, someone i know tried Zn/HCl on 2,5-dimethoxynitrostyrene, and got a low yield. He followed the procedure found on rhodium
- http://www.erowid.org/archive/rhodium/chemistry/leminger.htm...
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Nicodem
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Often, the yields of reactions repeated from other's written procedures are positively proportionally related to the theory understanding and
knowledge of the experimentalist (among other factors). This does not necessarily impute a telepathic connection between the experimentalist and the
mass of molecules in the flask, but rather all kind of other physical interactions all aimed at improving the reaction yield. I guess that is why a
chemists need to study a lot before he is good at what he does - otherwise just about any idiot could do this job.
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Barium
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| Quote: | Originally posted by Isomeric_Fred
Perhaps you omitted some important side notes which you deem basic or something and we just dont figure it out? |
What can I say? Therein lies the difference between the cook and the chemist.
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Isomeric_Fred
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| Quote: | Originally posted by Barium
| Quote: | Originally posted by Isomeric_Fred
Perhaps you omitted some important side notes which you deem basic or something and we just dont figure it out? |
What can I say? Therein lies the difference between the cook and the chemist. |
Wrote a very long and angry reply to your condescending answer to my above polite question, but as I hate seeing good board fall into flame-wars,
decided to delete it and wish you the best of luck in all your endeavours!
Have fun 
[Edited on 29-10-2008 by Isomeric_Fred]
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stoichiometric_steve
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| Quote: | Originally posted by Barium
What can I say? Therein lies the difference between the cook and the chemist. |
I must admit, i didn't expect such a snotty answer. Hats off to the uber chemist!
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Barium
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Steve/Fred
There is actually, believe it or not, a limit to my patience. I know of several members of the Hive who have successfully used my methods. Both well
trained chemists and simple cooks. By simple I mean people who have no idea what is actually happening in the rection vessel and why and are not
capable to modify a protocol to a new substrate or exchange one solvent for another. Yet Steve decided to solemly declare the CTH-reduction system
completely flawed and later, more or less openly call me a liar, when in truth he didn't even have the basic understanding how it worked. No Steve,
the potassium formate does not have to be dissolved in the IPA layer. Read the patent!
I have over the years gained some expertise in hydrogenations and can more or less perform them blindfolded, but I have a terrible track record for
Zn/formic acid and other dissolving metal reductions. A friend of mine can't understand how the fuck I can fail with those reactions when he rarely
gets a bad yield with them. Do I claim those methods bogus? No, why should I?
I gave a couple of examples of reasons why one person can get results another person can't reproduce.
| Quote: | | I report the yields I get. Why others have problems reproducing them can be due to a whole lot of reasons. It can be something as trivial as too low
stirring speed (especially in PTC-reactions), as well as wrong catalyst (like trying to use platinum instead of palladium) or the correct catalyst but
wrong support material (e.g. alumina instead of carbon). |
I have recieved complaints from several persons about the "really wet reductive alkylation" and without exception none of them had used the same
substrates as I had. Yet they expected the same yields I reported. That is simple cook mentality and understanding of the procedures. I am not, nor
have I ever been, interested in spoonfeeding information to people. If that makes me snotty and condescending, then so be it.
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starman
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I woukd of thought it important to remember that Barium's write ups are for the most part,minor modifications of publshed procedures.Reputable
laboratories,well credentialed chemists under peer review scrutiny,working with the best of equipment and materials.Even these guys get into pretty
heated debate in the literature as to the reproducibilty of a particular yeild or result.Sometimes with barely veiled accusations of massaging the
data.I think it fair to state there is a great deal of art in the science of chemistry.
Back on thread..... If the acid merely acts as a proton donor,is there a particular explaination why Zn/HCL will only reduce a terminal nitro whereas
Zn/HCOOH will reduce both intermediate and terminal nitros?
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stoichiometric_steve
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| Quote: | | Originally posted by starman If the acid merely acts as a proton donor,is there a particular explaination why Zn/HCL will only reduce a
terminal nitro whereas Zn/HCOOH will reduce both intermediate and terminal nitros? |
There is no explanation because this is not true, assuming that you are talking about saturated nitroalkanes. Zn/HCl does also reduce secondary
nitroalkEnes, but you get oximes and ketones instead of amines.
I've just successfully reduced a primary and a secondary nitroalkAne with Zn/HCl in IPA, and the yield was great (about 80% for each amine).
edit: This may be something some people are overlooking: A nitro group needs 6 electrons for complete reduction to the amine, hence you need 3 eq.
Zn(0) and 6 eq. H+ per nitro group.
[Edited on 30-10-2008 by stoichiometric_steve]
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