Zn-HCl reduction attempted!

[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.