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.