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Author: Subject: Experimental: Alternative to Al/Hg - the Al/Cu
Burner
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[*] posted on 14-5-2014 at 10:58


Quote: Originally posted by madscientist  
Better than many of the alternatives, that's for sure. But don't let any copper salts go down the drain - they're rather toxic.


Yes, I realize that, but since it is not consumed in the rxn I felt that it could be (re)used until the Al(OH)3 slurry got pretty thick. It would sure beat the typical process of using strong base and would make it much safer for children to use.
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organichem
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[*] posted on 15-5-2014 at 04:49
Reductive amination


I tried a reductive Al/Cu amination like Al/Hg with a ketone and nitromethane at 25 mmol scale but received no amine (only evolution of MeNH2 vapor when adding conc. NaOH)

Quote: Originally posted by madscientist  
It's also worth considering running these reactions in straight alcohol, or even aprotic solvents such toluene with the alcoholic proton source being added gradually.


I suppose it's due to too much water (+ acid) in the reaction preventing effective imine formation. What about the HOAc?
Probably the reaction could be tried in anhydrous MeOH/EtOH/IPA (of course CuCl2 has to be used then) and without any acid added (analogue Al/Hg)?

Another idea: why in general is a mixture of ketone/nitromethane added (with Al/Hg) - couldn't pre-formation of methylamine from nitromethane and subsequent addition of the carbonyl compound in alcohol give better conversion?
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[*] posted on 15-5-2014 at 06:48



Quote:

why in general is a mixture of ketone/nitromethane added (with Al/Hg) - couldn't pre-formation of methylamine from nitromethane and subsequent addition of the carbonyl compound in alcohol give better conversion?


I guess using nitromethane is more an "to kill two birds with one stone"-approach.

I assume using methanol+methylamine and molsieves while forming the imine first and reduce it afterwards would give better results, although there are reports on formation of imines in water and isolating them in good yield.
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[*] posted on 15-5-2014 at 13:53


Highly meso-Diastereoselective Pinacol Coupling of Aromatic Aldehydes Mediated by Al Powder/Copper Sulfate in Water

Yoshiharu Mitomaa, Iwao Hashimotob, Cristian Simionc*, Masashi Tashirod & Naoyoshi Egashiraa

Synthetic Communications. 2008, Vol. 38 Issue 19, p3243-3250.
http://www.tandfonline.com/doi/full/10.1080/0039791080211019...


nothing is new

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[Edited on 15-5-2014 by EdMeese]
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[*] posted on 15-5-2014 at 15:24


Quote: Originally posted by eidolonicaurum  
Forgive my ignorance, and the noobishness of the question, but what is the purpose of the glacial acetic acid? I've seen it used before in reactions, but I can never understand its purpose. Is acting as a solvent? If so, why ethanol and glacial acetic acid?


I've often wondered the same thing but Nicodem has given a clue given here.

Quote: Originally posted by Nicodem  
<snip>
In the reductions of nitrostyrenes with Hg activated aluminium, reducing the amount of Hg(MeCOO)2 or other Hg salts (e.g., <15 mg / g Al) <snip>


Is this Hg/acetic acid "coupling" the reason acetic acid is needed?
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[*] posted on 16-5-2014 at 02:55


While cursing at some stubbornly slow reactions yesterday (that needed to be done the day before yesterday) I decided to dig into the inorganics cabinet and flail away.

It appears the counterion is important in ways beyond mere solubility.

CuCl<sub>2</sub> (hydrate) and CuBr<sub>2</sub> (anhydrous) both afforded rapid reaction with aluminum foil or aluminum powder in water or dry methanol. Cu(OAc)<sub>2</sub>, Cu(NO<sub>3</sub>;)<sub>2</sub>, CuCl, CuI in MeOH had no effect on Al. CuF<sub>2</sub> did, but was only tested in MeOH, where solubility was poor. Discoloration of shredded Al foil was noted after several hours.

Aqueous solutions of nickel chloride and cobalt chloride had no effect on Al foil.

CuCl<sub>2</sub> in MeOH generated an amazing amount of hydrogen gas with Mg powder, while Zn dust afforded none - the solution simply turned colorless and Cu(0) dropped out of solution (though eventually it regained the copper color as, assumedly, atmospheric oxygen helped oxidize it and bring it back into solution - don't ask for details on how this would occur, because this is not my expertise :P).

I also tried chucking a couple obvious reduction candidates at CuCl<sub>2</sub> in MeOH, using either Al or Mg. At this point, I only have TLC results (I am one busy bee these days), but it appears Mg is not the way to go. Nitromethane, nitrobenzene, and 3,4-dimethoxyphenylacetonitrile were all exposed to these conditions - the reactions with nitrobenzene and Al powder were violently exothermic, and I returned from my desk to find a bit of a mess. :D I also (very sloppily and hastily) prepared an imine condensed from benzylamine and benzaldehyde, and pitched it in - it's going to need GCMS data to sort out, but the crude NMR with Cu still hanging around (which will cause chemical shift drift - really, very low on time, hence the sloppiness) suggests some reduction occured, but it's not enough to justify popping champagne quite yet. I've been deceived before.




I weep at the sight of flaming acetic anhydride.
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[*] posted on 17-5-2014 at 06:27


Quote: Originally posted by madscientist  
It appears the counterion is important in ways beyond mere solubility.

CuCl<sub>2</sub> (hydrate) and CuBr<sub>2</sub> (anhydrous) both afforded rapid reaction with aluminum foil or aluminum powder in water or dry methanol. Cu(OAc)<sub>2</sub>, Cu(NO<sub>3</sub>;)<sub>2</sub>, [...]


Well, yes. That's what woelen found (see link in OP's first post). Interesting that you found the same activity with copper (II) bromide, though...




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[*] posted on 18-5-2014 at 23:10


Quote: Originally posted by blogfast25  
Quote: Originally posted by madscientist  
It appears the counterion is important in ways beyond mere solubility.

CuCl<sub>2</sub> (hydrate) and CuBr<sub>2</sub> (anhydrous) both afforded rapid reaction with aluminum foil or aluminum powder in water or dry methanol. Cu(OAc)<sub>2</sub>, Cu(NO<sub>3</sub>;)<sub>2</sub>, [...]


Well, yes. That's what woelen found (see link in OP's first post). Interesting that you found the same activity with copper (II) bromide, though...

Yeah - I love these woelen's amateur descriptions:
....small pieces of household aluminium foil
...put some table salt
....add some water
....add a few drops
.....then a small amount of hydrochloric acid may be added, but not too much.

In general, it makes the experiment unreproducible, moreover addition of any acid leads to false conclusions.
Below my version of this experiment.
Mix (at r.t.) 3g of NaCl + 12g of H2O + 0,3g CuSO4x5H2O. It gives green solution. Add 70mg piece of Al foil (about 0,04 mm thick) and swirl all with glass rod.
Nothing interesting happens, Cu slowly precipitates as spongy brown-red deposit (especially on foil edges). Very tiny amount of H2 goes off from Al (and it lasts many hours - tested in one run).
One drop (~60 mg) of ~50% H2SO4 was added (it was at hand), It gave slightly faster H2 evolution, one more drop of conc HCl gave additional increase of H2, but still very slow.
Then additional 0,3g portion of CuSO4x5H2O was added - it caused more H2 evolution, another 0,3g - more H2, another 0,3g - more H2. Now H2 evolves quite violently. Cu deposit is now less spongy and more rose-coloured, the mixture becomes warm and deeply ("dirty" I would say) green. When more Al is added, reaction soon ends with colourless, milky (+Cu spong) solution.
When amount of Al is limited, reaction ends with deeply brown solution. I have seen seen such colours many times - clear indication of Cu(I) complex.
It also explains activity of Cl and Br anions and nonactivity of acatate, sulfate, nitrate... etc anions, because Cl or Br gives (relatively) stable and soluble complexes with Cu(I) in concentrated NaCl (or surely bromides also) solutions.
Clearly, mechnism of Al activation by Cu is more complex and most possibly includes Cu(I) species.

Continuing the off topic: Mg/methanol reducing system - unfortunately in German, old (1929) article from Annalen.
Über die Anwendung von Magnesium und Methylalkohol als Reduktionsmittel


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Klaszczę w dłonie, by było mnie więcej....
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[*] posted on 19-5-2014 at 01:05


Quote: Originally posted by madscientist  

Have you tried running this reaction in neutral media, as they did in the SynLett posted by kmno4? (Or gradually adding AcOH merely to maintain acidic pH). Extractions are (obviously) easier with less AcOH to deal with. Might not be such a bad idea either to quench with aqueous ammonia, to displace any of your product that may be coordinating to copper and complicating extraction


Actually yes it was tried without AcOH as well a couple of times, but the yield seem to come in a bit lower so it was given no further thoughts.

Quote: Originally posted by Burner  
Quote: Originally posted by madscientist  
Better than many of the alternatives, that's for sure. But don't let any copper salts go down the drain - they're rather toxic.


Yes, I realize that, but since it is not consumed in the rxn I felt that it could be (re)used until the Al(OH)3 slurry got pretty thick. It would sure beat the typical process of using strong base and would make it much safer for children to use.


The copper salt does get used (not a catalyst) and at the very end of the reactions as all is poured out, one can observe solid copper particles in the bottom of the flask.
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[*] posted on 1-6-2014 at 06:59


To good to be true, but i gave it a run.
2,5 gr Al
50 ml water
2 gr phenyl-2-nitropropene
100 ml AcOH
1,5 gr CuCl2
Long story short - after workup i got 70mg of phenyl-2-aminopropane.
So it's waste of time/=

[Edited on 2-6-2014 by polsaer]
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[*] posted on 1-6-2014 at 16:34


So quick to discredit a method! It's good to be skeptical, but one run is scant evidence. Some reactions are finicky and need some fine adjustments an attention to detail to get to go properly. Did you forget to use alcohol as solvent, or did you just forget to mention it? I haven't worked with nitrostyrenes or phenyl nitropropenes before, but I doubt that they are appreciably soluble in water. I imagine that would put a big kink in things.
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[*] posted on 1-6-2014 at 23:13


They are soluble in AcOH for some extent, and Al/Hg works perfectly without using alcohol as a co-solvent.
There are posts on hyperlab about Al/Cu - also with unsatisfactory results.
It certainly works but personally i don't believe in 70% yields

P.S Maybe it works only on nitrostyrenes like Zn/Hcl.

[Edited on 2-6-2014 by polsaer]
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[*] posted on 2-6-2014 at 00:57


Quote: Originally posted by polsaer  
...
There are posts on hyperlab about Al/Cu - also with unsatisfactory results.
...


Can someone with better Internet search skills than myself please post a link to the hyperlab thread.
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[*] posted on 2-6-2014 at 09:58


In the Hyperlab post [540004] from 21. Sept. 2010, the member ruzer describes what is a method most similar to that reported by TheCopperMan. He reduces 2-(2,5-dimethoxyphenyl)nitroethene in a no less than about 70% yield (the exact yield cannot be determined because he did not analyse the crude product for purity, instead he derivatized the crude product as such).

All the previous attempts reported misserable yields or no isolated yield whatsoever. It is hard to say if this is due to the substrate used or due to the different method. In some reported failures, the inapropriate isolation might be the cause. Only few members at Hyperlab worked on this problem since the first mention in 2006 (see post [498996] and follow up) and very little progress was made before ruzer's report. The fact is, that if it were not for the lack of interest, the reduction method would have been well research till now.

PS: I find it interesting that the articles using this metal dissolving system appeared only after the initial 2007 publication at Sciencemadness, yet none of them cites it. Looks like those academic snobs refuse to cite us. If I weren't one of them I would spite at them!
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[*] posted on 2-6-2014 at 16:22


Nicodem, thank you for the references and above all, your commentary (as always).
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[*] posted on 3-6-2014 at 06:48


Somebody should try it on various phenyl-2-nitropropenes(plain, 2,5-, 3,4- e.t.c)
We clearly have not enough information.
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[*] posted on 3-6-2014 at 11:05


Quote: Originally posted by polsaer  
To good to be true, but i gave it a run.
2,5 gr Al
50 ml water
2 gr phenyl-2-nitropropene
100 ml AcOH
1,5 gr CuCl2
Long story short - after workup i got 70mg of phenyl-2-aminopropane.
So it's waste of time/=

[Edited on 2-6-2014 by polsaer]


Please try it as per the original writing. Use 300ml EtOH, 120ml water, 45ml or more GAA for every 20g styrene. Pre-heat it to 60C along with 15g Al, then add in the CuCl2 and it should start a vigorous reaction for 10+ minutes, then reflux for one hour under stirring and at the end, preferrably steam distill it in-situ. A lot of people (yes A LOT) mess up the solvent extractions one way or another.
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[*] posted on 3-6-2014 at 12:26


Well, my interest is sufficiently raised. I will see if I can form the nitrostyrene from vanillin, and give the reduction a try with that.
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[*] posted on 4-6-2014 at 01:05


Quote: Originally posted by TheCopperMan  

Please try it as per the original writing. Use 300ml EtOH, 120ml water, 45ml or more GAA for every 20g styrene. Pre-heat it to 60C along with 15g Al, then add in the CuCl2 and it should start a vigorous reaction for 10+ minutes, then reflux for one hour under stirring and at the end, preferrably steam distill it in-situ. A lot of people (yes A LOT) mess up the solvent extractions one way or another.


All my p2np is gone now, can you try this reduction by yourself on nitroPROPENE? In my opinion it certainly works for nitrostyrenes, but propenes are matter for discuss.
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[*] posted on 6-6-2014 at 19:55


@TheCopperMan - when you say steam distill, do you mean external (live) steam with a steam generator, or internal steam distillation? My 3-methoxy-4-hydroxy-betanitrostyrene is crystallizing, so I should be able to try this method tomorrow.
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[*] posted on 7-6-2014 at 10:44


@Crowfjord Steam distill it internally. Just add a bunch of water and heat it, re-add water occasionally, take readings of distillate coming over (PH or etc) to check when everything has been distilled out. Works like a charm.

@polsaer It works on nitropropenes. That is all that can be said. Re-try it as per the writeup, it will work.
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[*] posted on 8-6-2014 at 02:26


Crowfjord, 3-methoxy-4-hydroxy-beta-nitrostyrene is a terribly bad choice for a model substrate. The corresponding reduction product will be very difficult to isolate. It's partition will require very efficient solvents (MeTHF, n-BuOH, etc.) otherwise it will not get extracted from water. You will also have to correct the pH to 8-9, but not more than that (the product is an acid as well as a base).
You would have done better to first alkylate vanillin with some easy to make or acquire (O-ethyl or anything higher would make the product nicely hydrophobic and easier to isolate).
Quote: Originally posted by TheCopperMan  
@Crowfjord Steam distill it internally. Just add a bunch of water and heat it, re-add water occasionally, take readings of distillate coming over (PH or etc) to check when everything has been distilled out. Works like a charm.

It is not possible to steam distil compounds that are relatively well soluble in water unless they form an azeotrope with water.




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[*] posted on 8-6-2014 at 10:16


Good points, Nicodem. I did figure that it would be a bit of a challenge. I want to give it a try anyway, but maybe I'll see if I can methylate some vanillin to veratraldehyde as well, and go from there. Hmm, I wonder if the vanillin nitrostyrene can be O-alkylated in a facile manner?
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[*] posted on 9-6-2014 at 17:22


I would be stupid not to follow your advice, Nicodem. This weekend I will make some ethyl bromide to alkylate with, rather than the methyl. No need to aggravate myself working with gasses (though I'm getting the hang of it) just to verify a procedure, when a simpler solution is available.

(Please pardon the double post)
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[*] posted on 10-6-2014 at 12:09


Quote: Originally posted by Crowfjord  
I would be stupid not to follow your advice, Nicodem. This weekend I will make some ethyl bromide to alkylate with, rather than the methyl. No need to aggravate myself working with gasses (though I'm getting the hang of it) just to verify a procedure, when a simpler solution is available.

I'm not saying that 4-hydroxy-3-methoxy-beta-nitrostyrene is useless. If you had access to an HPLC then it might be just fine as a substrate (provided you had a column suitable for polar amines - not all work). However, for an amateur situation where you need to tediously isolate the product in order to do an optimization study, you would do better with a more suitable substrate. 3,4-Dimethoxy-beta-nitrostyrene might be OK, depending on the work up method and extraction solvent (it would not do well with toluene, but ethyl acetate after reaction mixture filtration, concentration, dilution and basification should be OK). Higher homologues 4-alkoxy-3-methoxy-beta-nitrostyrenes where the alkyl is ethyl, propyl, isopropyl, benzyl (etc.) would be best for a rudimentary setting as you are at least sure there are only insignificant losses during the isolation.

Ethyl bromide is quite volatile, but doable with a good condenser. If you have n-propanol it would be more practical to do the less volatile bromopropane. 2-Bromopropane from 2-propanol sounds attractive, but it is poorly reactive and O-isopropylation of vanillin would optimally require DMF or NMP as a solvent. Benzyl chloride from toluene is also very simple and reactive enough. It would also say something about a possible debenzylation issue under the reaction conditions (I don't really expect any, but it is good to verify this possibility).




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