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Unexpected increase in precipitate after zinc reduction

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Jagube

Jagube

Esteemed member
I did a zinc reduction on my harmaline/harmine fb extract from rue.

After filtering the acidic solution (didn't measure the pH, but must have been around 2.5 as I used 5% vinegar with no extra water) I based it by adding a saturated solution of sodium carbonate until it reached pH 10.4.

I let it sit for almost 24 hours and was surprised to see that there was much more precipitate than the alkaloids I started with - roughly 10 times more volume-wise.

I wonder what this precipitate is? The only things added to the initial alkaloid powder were vinegar, zinc and sodium carbonate.

Also, has anyone had luck dissolving their mix of THH/harmine/harmaline fb in carbonated water to separate the alks from the zinc?
 
Unexpected increase in precipitate after zinc reduction?
Not so 'unexpected' actually, the zinc salts do form.
Can't find my spoon :cry:
 
Redissolve in vinegar, base with ammonia. Zinc salts will form at first but as the pH rises more, they will go back into solution. Stir continuously and add ammonia slowly, drop by drop.
 
I was expecting some increase, but not that much. Zinc carbonate must be very fluffy.

ijahdan said:
Redissolve in vinegar, base with ammonia. Zinc salts will form at first but as the pH rises more, they will go back into solution. Stir continuously and add ammonia slowly, drop by drop.
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Do I need to add ammonium chloride as well, or will just ammonia do?
 
Jagube said:
...Do I need to add ammonium chloride as well, or will just ammonia do?
Click to expand...
The ammonia chloride might work (?) but is complete unnecessary, you don't need that as ammonia on its own brings the zinc salts back into solution before the thh start to precipitate, ijahdan just said it. Ammonia to near pH 10 and you're set. Filter and wash (with a 1 to 3% ammonia solution or 0.5% sodbicarb.)
 
Thanks. Is "household ammonia" ok to use for this purpose in regard to food safety?

Here is another thought...

According to this post by Phlux, THH precipitates at pH 6.9. My tap water is pH 8.8. If that's true, then by diluting my filtered acidic solution with tap water I should be able to bring the pH to, say, 8, and cause the THH to precipitate, without precipitating any zinc salts?
 
My household ammonia is OK, dunno about yours.

Don't jump wagon on dead ending threads. Mostly they are nice ideas which is good and cute and learn-some, but why did that thread stopped with unfinished works? Where are the goodies?

Tap water to base: you would need so much water that the concentration goes so low that precipitating gets compromised. Why don't you check? Take 100ml vinegar, add tap water to the desired pH and look at how much you needed. I suspect it's going to be a lot.
 
If you're not sure that your ammonia is pure, there is a way to purify which Im going to try soon. Starting with concentrated household ammonia, (mine says '18-33%' concentration), put some in a wide, shallow, open-topped container, ie a bowl or dish, then put the same amount of distilled water in a similar container and place both containers in an airtight box. In a couple of weeks, the distilled water will have become purified ammonia solution at half the concentration of the original one (which will now also be half its original concentration).
 
ijahdan said:
If you're not sure that your ammonia is pure, there is a way to purify which Im going to try soon. Starting with concentrated household ammonia, (mine says '18-33%' concentration), put some in a wide, shallow, open-topped container, ie a bowl or dish, then put the same amount of distilled water in a similar container and place both containers in an airtight box. In a couple of weeks, the distilled water will have become purified ammonia solution at half the concentration of the original one (which will now also be half its original concentration).
Click to expand...
Cute, I knew this one from muriatic acid, good idea to try on ammonia.
:thumb_up:
 
ijahdan said:
If you're not sure that your ammonia is pure, there is a way to purify which Im going to try soon. Starting with concentrated household ammonia, (mine says '18-33%' concentration), put some in a wide, shallow, open-topped container, ie a bowl or dish, then put the same amount of distilled water in a similar container and place both containers in an airtight box. In a couple of weeks, the distilled water will have become purified ammonia solution at half the concentration of the original one (which will now also be half its original concentration).
Click to expand...
Thanks, that's interesting. I wonder how it works? Presumably the ammonia evaporates and is somehow sucked up by the water?

Update: I washed the basic soup several times to reduce the pH, and not much of anything happened for like 7-8 washes (other than the pH dropping slightly), and after another wash most of the precipitate suddenly dissolved... so from the initial 10x volume I'm now down to like 2x volume. Wow!
Maybe the sodium zincate is now all or mostly dissolved to the point I don't have to worry about it? I'll do another wash for good measure and check if the volume drops further.
 
A large volume of the precipitate dissolved around pH 9.4 - 9.6.

Further washes, which brought the pH down to 9.2 (my tap water is pH 8.8, so using it it's hard to bring the pH below 9), didn't decrease the volume of the precipitate to a measurable degree. So I'm assuming all (or most) sodium zincate is gone, and what is left is relatively pure alks.
Could this be an easy way to get rid of sodium zincate, or am I being too optimistic?

I'm drying my precipitate and once dry I'll weigh it, then dissolve in vinegar, base with ammonia, dry and weigh again to compare how much the weight has changed. If there is little change, it will mean simple washing the alks with water removes all or almost all sodium zincate. Of course some change is expected due to losses (alks sticking to jar walls etc.)
 
Jagube said:
...Maybe the sodium zincate is now all or mostly dissolved to the point I don't have to worry about it? ...
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Sodium zincate dissolves is water, no problem there, it is the zinc carbonate that tends to precipitate under basing. Heavy basing turns it back into the liquid and ammonia is the best candidate. Nor sodcarb nor lye does as well.

Awaiting the post-ammonia results :thumb_up:
 
Jees said:
Sodium zincate dissolves is water, no problem there, it is the zinc carbonate that tends to precipitate under basing. Heavy basing turns it back into the liquid and ammonia is the best candidate. Nor sodcarb nor lye does as well.
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That link is for sodium acetate, not sodium zincate.

But yes, my bad... it was zinc carbonate that made up the bulk of the precipitate. And that bulk is gone. I'll post the post-ammonia results as soon as I have them.
 
Jagube said:
...That link is for sodium acetate, not sodium zincate...
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OOps, yet it is sodium acetate that we have (in solution). The thing we try to evade is the precipitation of the zinc carbonate (edit: I see you just wrote that, OK.), no other stuff tends to fall out. There is ammonia the best. This is not theoretical but straight practical experiences.
 
Well, initially I based to pH 10.2 and got like 100mm of precipitate in the jar. After washing several times the pH dropped to 9.8 and the volume of the precipitate didn't change. One more wash and the precipitate suddenly shrank to 27mm (pH 9.7). Then yet another wash, pH 9.4 and only 19mm of precipitate. Further washes didn't reduce the amount of precipitate.

Whatever it was, it dissolved completely (or almost completely) at around pH 9.4 - 9.6. It doesn't match the behavior of zinc carbonate, which is supposed to dissolve as the pH increases to 10, not as it drops (with ammonia anyway). Could it be that zinc carbonate behaves differently when sodium carb is used as the base?
 
Precipitation with sodium carbonate is a tricky thing because its solutions contain a significant concentration of hydroxide ions. The upshot of this is that, in this case, we get basic zinc carbonate, which is a mixture of the carbonate and the hydroxide. This happens with most metals that have insoluble hydroxides and carbonates, thus precipitating pure 'neutral' carbonates is actually quite difficult. (It can sometimes be achieved by using bicarbonate and heating gently but that's not really relevant here, I think.)

So, what I'm saying is that you may be seeing the hydroxide component dissolving more readily - especially if it is freshly precipitated - and maybe there wasn't that much carbonate in your precipitated zinc hydroxide.
 
Jagube said:
...Whatever it was, it dissolved completely (or almost completely) at around pH 9.4 - 9.6. It doesn't match the behavior of zinc carbonate, which is supposed to dissolve as the pH increases to 10, not as it drops (with ammonia anyway)...
Click to expand...
If we have learned one thing that is one can NOT make claims about pH points where which does what. Change base and/or change concentration and/or change other components in the mix and your numbers are down the drain. It's a lively balance of many influences. Not to mention the correctness (or lack thereof) of the used pH meters and their ditto calibration. I've found experimental wise that zinc carbonate re-dissolves sooner in ammonia than any other base. Don't ask me why.

During basing you should see first mist forming (that's the zinc carbonate), further basing --> clearing of that mist. More base then suddenly again precipitation which is your goodies. That is your reference, not numbers per se. You should observe the process and rely mostly on that.
 
I redissolved my precip and was surprised to see how impure it was.

After dissolving in hot vinegar and stirring, there seemed to be two undissolved components left: the usual brown/reddish plant impurities, suspended in solution (which subsequently got caught by the filter), but also a grey powder that settled at the bottom.

I suspect the grey stuff is a zinc compound, but why didn't it get removed when I filtered the acidic soup right after the zinc reduction?

I added ammonia to bring it to pH 10.4 for good measure. Should I keep the lid on the jar closed tighly (because the ammonia will evap, lower the pH and the zinc carbonate will go back into solution), or open it to let any gases out? The jar is sitting in an unheated shed, where the temperature is around 8C / 46F at the moment.
 
The initial 4.6g, after re-dissolving in vinegar, filtering, re-basing with ammonia and washing, turned into a measly 0.44g. And it's a very dark brown.

I'm not sure about this ammonia thing...

The washes I poured out glowed strongly in UV. Maybe instead of washing I should have evapped it?
 
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