Zn-HCl reduction attempted!

[Bandil]

Hi!

Swim attempted to do the Russian Zn-HCl reduction presented in earlier posts. 6 gm sparkling orange 2,5DMNS was reduces following the prodecured mentioned. When it was done, some orange gunk floated on top of the solution. The filtrate was clear yellow. When basified, it turned milky white. I suppose this is a good sign?

@Sunlight> Does this match your experience?

Thanks!

Regards
Peter

[Bandil]

Thats weird... I basified(pH 8-9) and extracted three times with DCM. It was quite hard to separate the phases beacuse af all the white gunk. The i destilled of the DCM at atm. pressure. Then applied some vac and brought off the water at 35 deg. When the water was gone, the RBF was filled with a lot of white powder, but no freebase 2CH had come over. Could the white power be 2CH on some salt form? wtf happened here?

thanks!

[megamole]

Bandil,

What did you use to basify? If you basify with NaOH or KOH, you'll precipitate Zn(OH)₂, which is a fine white milky precipitate that will make your life hell. However, if you use ammonium hydroxide solution (ammonia water), it will chelate with the Zn(OH)₂ to form a water-soluble complex, making the work-up possible.

[Bandil]

Yes, i used NaOH for basifying. Im pretty sure practycally nothing was reduced as alot of nitrostyrene floated on top of the soln and nothing appeared when distilled.

What about using Zn/Hg, does that have better chances of success?


Regards
Peter

[Rhodium]

Don't be so impatient. Try the same but work up with 25% ammonia instead of sodium hydroxide, and see what you get.

[Bandil]

How come there where so much unreacted nitrostyrene left i the soln? It floated right on top of the whole mess, and there were quite an amount. A lot of references uses a lot more alcohol to make it dissolve.

Swim will make another batch DMNS tonight and attempt reduction again tomorrow...

Regards
 Peter

[sunlight]

Yes, more or less. If there was orange it is unreduced material or partially reduced. In my first test there was nothing orange, and solution was almost colorless, but in other attempts with less Zn I got what you say. How much Zn did you add for the 6 grams ? I've got after my first test 30%-36% always using 3-4:1 excess of Zn.
Ok completely with the milky solution.
I'm just trying something similar, with a excess of 6:1 Zn w/w, and I've thought in filter the hydroxides too. Are they easily filterables or you added alcohol to make them more consistent ?
I'm worried about I could make mistakes in the first test and yield is not a 60 %, but in some hours we'll know. Tomorrow you'll have the exact result of this rxn.

[Bandil]

I guess i made a mistake in the reduction:

When adding the Zn/Hcl Swim did it over 0.5 hr's. It foamed some(1 cm), and the foam seemed to be mostly DMNS. I suppose much of the DMNS was ontop of the solution, not being reduced. The proper amount of time to add it over is 4 hours, right? Should i just stirr so hard, that all of the red gunk is pulled into the soultion, or add more alcohol, to make it soluble?

Thanks for your patience!

Regards
Peter

[hypo]

stupid question about Zn hydroxides: doesn't the stuff redisolve if you add lots of NaOH? i *believe* i have seen something like this, but then i dont know if it wasnt maybe Al. or if i was dreaming... ??

[sunlight]

The white powder is the carbonate of 2CH, it is formed readily in contact with air. You got something sure, not too much if there was orange gum at the end, but something.
How much Zn did you add ? I think it's important and please, I want to know it.

[sunlight]

I use to add some alcohol to avoid foaming, if not the rxn is not elegant and I guess less reproductible.
How much Zn, please ?
Rhodium, I've tried tha NH3 basification, but it didn't worked, or at least it was not the oil floating on the top like with NaOH. It was a small test, 50 % basified with NaOH and 50 % basified with NH3, and the oil appeared with NaOH and not with NH3, I didn't make the work up with this 1 gram escale, it's too much for me.

[Rhodium]

You must extract the phase with a non-polar solvent after basifying with NH3 to recover your product (then wash the non-polar with brine). Don't expect the amine to isolate itself.

[sunlight]

But when using NaOH the amine it's floating, why this difference ?

[Rhodium]

Perhaps because of the different ionic strenghths of the bases, or perhaps the ammonia solubilizes the other amine by some kind of complex. I think somebody else should have a more detailed explanation, but I am not surprised that different kinds of bases (hydroxide being a bronsted base, and ammonia being a lewis base) gives different physical results. Perhaps Osmium or Megamole knows?

[sunlight]

I thought about Zn-ammonia complex, NH3 dissolves Zn and so may be some kind of thing is formed that solubilizes the amine, and perhaps it can't be extracted (just an oppinion). So I decided to forget this way, but may be it works.

[hest]

I'm sure that NH3(aq) is alot less polar than NaOH(aq), so the amine is more sol. in the NH3 solution.

[sunlight]

But NH3 is often in the work up of amines, so do you think that it could be extracted as usual ? NH3 could facilitate the work up, but if we have to use more solvents for extractions, we are in a similar case.

[Bandil]

I used the following:

5,32 g MDNS
56,6 mL H2O
21,24 mL 30% HCl
26,5 IPA

and added:
180 mL 30% HCl
38,3 g Zn dust

The Zn powder was really old(10 yrs), but was sealed airtight, so i guess that was ok.

Do you think that i should pour in some Hg salt for next run? How about more alcohol or more stirring?

I extracted the phases with DCM, and the lower DCM phase was virtually impossible to separate because of the Zn(OH)2. Whats the verdict? Should i use ammonia for basifying or just add ALOT of sodium hydroxide?

Thanks!

Regards
Peter

[Rhodium]

I definitely believe it could be extracted as usual. Most of the NH3 will stay in the water, and the phenethylamine will get carried over into the non-polar layer.

Make sure you use enough NH3, as it is a weak base, it is harder to achieve a high pH with it that with NaOH.

[hest]

Yep, and remember to wash the non-polar with brine once.

[Rhodium]

No Hg salts, please.

[sunlight]

a) Wich pH could be enough ? When I tried it I was surprised of the quantity of 25 % required for pH 11.
b) Ammonia is soluble in toluene, DCM, ether. I think a saline wash won't be enough if we have a lot of solvent, so we need to evaporate all solvent, what do you think ?
I think that adding alcohol to the Zn hydroxides can convert them in filterable solids, based in a very small test. Then we would have the standard Al/Hg work up, evaporate alcohol, extrat ...
Bandil, it seems ok and the ratio Zn:25DMNS is 7:1, you should end with no orange tar and a transparent light yellow solution. May be the problem is the ratio of adition. I have now with a 6:1 this stiring with a bit of Zn-thing not dissolved yet, it need more hours.
Tomorrow you'll have the details of a run and yield. We'll see how good is this.

[Rhodium]

Ammonia is soluble in those solvents, but it is MORE soluble in water, so there are no excessive amounts transferred. A saline wash or two would be enough in my opinion.

[Bandil]

So you think i should add the Zn-HCl slower? Perhaps over the course of 4 hrs, while stirring like a madman, to keep the DMNS in the solution? I guess the Zn-HCl should be added as such a ratio, that they will be added completely at the same time after a couple of hrs?

Ill make the large DMNS tomorrow, so i have for a lot of 1 gm batch runs. While im at it, ill try the electrolytic reduction of the NS.

Regards
Peter

[Osmium]

Each Zn ion needs at least two NH3 (?) to form the complex, probably much more to shift the equilibrium Zn/Zn diamine into the desired direction. Product freebase might also take part in this Zn complexing, another reason why excess NH3 is desirable. Then base strenghts of primary amines (MDA or whatever) and ammonia are sorta comparable, meaning more NH3 is needed in this equilibrium for complete freebasing of the organic product. 25% NH3 should be around 13mol/l, a concentration comparable to conc. NaOH. But since NH3 isn't a very strong base much more is needed to further raise the pH. I guess that's why so much aq. NH3 is needed to reach pH 11 (or whatever is desirable for clean workup).

The comparable pKb values (base strenghts) of organic amines and NH3 might be the reason why the freebase isn't separating in this reaction, since it isn't in the form of the freebase long enough to form bigger agglomerates (droplets) which would then separate. It sorta is changing into the protonated form and back to the freebase under those conditions unless you added large excesses of NH3 to shift the equilibrium into the desired direction.

Just a theory, hope it makes sense to at least some of you  

[moo]

Why not Zn(OH)₂ + 2OH^{- __}> [Zn(OH)₄]^2- instead?
^{understanding is everything}

[Rhodium]

That is also a possibility.

[sunlight]

It seems that there's no way to make the work up more optimized, doubts with NH3 and furthermore, to work with lots of NH3 is terrible.
I've tried my idea of adding alcohol to precipitate the hydroxides and it didn't work with reeasonables amounts of it, so I fucked the work up. I evaporated part of the methanol and tried toluene to extract and I have emulsions that slowly separates, I can finish it but need more time. The final basic solution with not all hydroxides dissolved is about 1700 ml, for 10 grams...
Bandil, if you want to try this rxn, I propose you this:
Make a solution of 12 water, 36 methanol (IPA) and 8 HCl 36 %. When it si at 25 C add 10 grams of powdered nitro (coffe grinder) and stir. At 25-30 add 60-70 grmas of Zn and 213-251 HCl 36 % , with the first 30 grams add 33 ml of HCl and with the rest 38 ml of HCl, the idea is to add 3.3 ml for each gram in the first 30 grams and 3.8 ml with the rest, in small portions. You can make it as you want, but try to keep this adition ratio and add all in about 2-3 hours. Keep the temp ok and don't add small portions specially in the beginning, you can use a big syringe for the HCl or it you have and ad. funnel, of course. Then let stir 4-8 hours, or less if all is dissolved, and probably you'll have a bit of Zn-thing undissolved in a transparent slightly yellow solution.
Unfortunately it can be washed with DCM because the similar density and toluene doesn't remove too much, but make 2x20 toluene, add enough NaOH 25% cooling to dissolve if not all the most of the hydroxides and you'll have a big solution-suspension to extract, wash the extracts wihh NaOH 25 %, brine, dry and xtallize.
The initial solution is small in order to keep the HCl conc. in an adequate range adding less HCl to finish with a smaller volume, but the density is so high that DCM doesn't work.
If you only have HCl 30 % use PM and I'll give the adequate ratios, I've it in Excel.
Good luck and tell us what happened. You got some carbonate of the amine in your first attempt. If you evaporate all solvent it is formed realily. When you finish the work-up you see carbonates in any flask where the solvente  with the amine has been.

[sunlight]

Ok, the ammonia works. I've taken a small sample of a few mililiters that I still had from a test, and added NH3, and finally the amina is floating on top at pH 10. May be too much ammonia is required, I haven't measured it properly, but it can be calculated. It's horrible to work with ammonia, but if it makes the extaction reasonable..
In my previous test, seeing that nothing happened with my estimated amount of ammonia, and pH was 9 or so, I added NaOH solution, the hydroxides didn't appear, pH was 12 and no amine (?), but in the other sample with only NaOH it was floating.
I feel like if I start to be boring for you with this story, with contious imprecisions and mistakes and my limited english. I ask you for your patient and your knowledge and experience, I'm no more than an amateur working alone and furthermore I'm very excited.

[Osmium]

The basifying doesn't have to be done by the NH3 alone. As long as there is enough NH3 around to completely convert the Zn to the complex the additional OH(-) can be supplied by NaOH too (or you try to dissolve the Zn stuff with excess strong NaOH only). Maybe that approach is more promising, resulting in a less bulky solution. Just guessing.

[Bandil]

I suppose the buffer-like tendensies the solution showed, was beacuse of the (Zn(OH)4)2- forming? I never god the pH over 8 or nine and i poured alto of 10% NaOH in it.

Regards
Peter

[sunlight]

That is because the amount of NaOH needed is really big. You have to convert all the ZnCl2 in Zn hydroxides, and then dissolve the hydroxides, finally you have a big milky solution with a pH 14.