[AmateurGuy]

This may be a tricky, non-straightforward question. If this is the wrong forum for it, please feel free to move it as necessary. I have posted here to reflect my approximate level of chemistry knowledge.

I work at an archeology lab processing soil samples to extract their phytoliths. As a part of the process, I use a solution of zinc iodide heavy liquid (2.3g/cm^3)to separate the phytoliths from the processed sediments in a centrifuge.

The lab is privately owned and operated, working on a small scale. Zinc iodide tends to be quite expensive, so to save my friend/employer money, I'm synthesizing it from dirt cheap zinc sulfate and potassium iodide.

For the most recent synthesis I dissolved both powders separately in RO water, then combined them and stirred gently while heating. A large quantity of what I hope to be potassium sulfate precipitated out of the solution, settling as a thick sludge on the bottom of my 1L beaker. I filtered the remaining liquid, then heated again to drive off excess water. However, this solution still has dissolved potassium sulfate/zinc sulfates remaining, of course. I intend to add denatured alcohol in the form of shellac thinner to precipitate any remaining sulfate.

My current product is 300 ml containing approx. 460g of Zinc Iodide (assuming my synthesis even worked, and the yields were ~95%+).

1. How important is the amount of water remaining for purposes of precipitating the sulfates? If necessary, I can drive off additional water with heating. If the water isn't a serious issue, I will be using Everclear (cooking ethanol 151 proof) rather than shellac thinner. Shellac thinner seems to have some possibly sulfur compound added as a denaturant. As a result, the end product heavy liquid retains an unpleasant odor that never seems to go away. Ever.

2. Are there any tricks for determining how much ethanol I will need to add? Presumably the important thing for sulfate solubility is the ethanol/water ratio in my solution... I expect it shouldn't take very much, but I need to be sure I've gotten 99%+ of the sulfates removed. Any remaining sulfate acts as a coagulant, causing the heavy liquids to form a strange sludge/gelatin when mixed with soil samples (in my experience at least. I really don't know very much about sulfate's coagulant action).

3. Alternately, if no easy answer exists for the previous questions, I can simply drive off all the remaining water and add either shellac thinner or Everclear to dissolve the zinc iodide. However, I'm having trouble finding information on the solubility of zinc iodide in alcohol. I would assume its quite high but... having no guideline figure, I'd just be guessing how much to add. This method is also not preferable due to the sulfate/iodide solids forming a cake that may trap some of the iodide within it, even after the addition of alcohol. Maybe the ethanol would penetrate through and dissolve it anyway?  This would also require hours of heating.

My apologies if this comes across as trying to get anyone to do my work for me- I'm just not quite sure where to go for chem help like this.

[billnotgatez]

http://en.wikipedia.org/wiki/Denatured_alcohol
http://paddler99.trailstories.com/fuel.html

just did some WIKI and GOOGLE

[AmateurGuy]

http://en.wikipedia.org/wiki/Denatured_alcohol
http://paddler99.trailstories.com/fuel.html

just did some WIKI and GOOGLE

Was I supposed to have noticed something on those pages?

[Arkcon]

Briefly, you haven't done enough research with commonly available resources, is where billnotgatez: may be going with his response.  Searching myself, I quickly find what I'd suspected, that potassium sulfate is soluble in water.  So mixing two water soluble salts, and hoping to get a reaction to two soluble products, is not possible, because the ions simply say in solution.  This page here tells us how its made industrially, and you should start with one of those two methods.

http://en.wikipedia.org/wiki/Zinc_iodide

[AmateurGuy]

Briefly, you haven't done enough research with commonly available resources, is where billnotgatez: may be going with his response.  Searching myself, I quickly find what I'd suspected, that potassium sulfate is soluble in water.  So mixing two water soluble salts, and hoping to get a reaction to two soluble products, is not possible, because the ions simply say in solution.  This page here tells us how its made industrially, and you should start with one of those two methods.

http://en.wikipedia.org/wiki/Zinc_iodide

Hmm.  Well, now I'm really confused.  When I add my solutions of zinc sulfate and potassium iodide to each other, I get a large amount of white precipitate and the solution changes color, so something is definitely happening.  Additionally, with the amounts of water involved, I would expect zinc sulfate and potassium iodide to both stay happily dissolved, especially when I heat the solution.  Potassium sulfate, on the other hand, is much less soluble than zinc sulfate, potassium iodide, or zinc iodide.  It's said to be approx 11g/100ml@20, whereas zinc sulfate is at 57g/100ml@20, and of course the iodides are extremely soluble.

I've already done this reaction a few times before, and the product I end up with certainly seems to be zinc iodide, or at least contains a significant amount of it.  The color is right (what else formed from this reaction would create a dark red solution?), the solubility in water is right, the dry appearance and weight are right... and its the only product I can think of that is soluble in ethanol.  Zinc sulfate, potassium iodide, potassium sulfate.. all insoluble or only slightly soluble in ethanol.  Whatever my product is, it dissolves readily.  Not knowing exactly how soluble its *supposed* to be in ethanol (that being part of my original question) I can't test to see whether it matches exactly...

[Arkcon]

Simply put, I wouldn't do it your way.  Yes, by manipulating the concentration and temperature, you get the least soluble of them all to precipitate, and the most soluble of the four reagents still in solution.  But the product, even if gently rinsed with water is still likely very contaminated with the others.  I don't have a reference handy for the solubility of each of the four in ethanol, so I can't be sure how well you can rinse impurities away.  Some online references may be able to help you better.

But you're not using lab grade ethanol -- you mention denatured ethanol, as if it were only one formulation, there are many, with different properties.  And then Everclear^TM -- beverage-grade ethanol, which isn't really pure, just guaranteed non-toxic, it contains a small, and random, quantity of water.  Furthermore, you want to buy a beverage, and pay the liquor tax for drinking it, and then not drink it.  No one in industry does that.  No school teaches that.  I don't know about that.  No one does.  Years from now, someone will Goggle this post and offer an opinion, but his mailing address will likely be Toothless Joe, Prospector, Behind the third big rock, Unimproved trritory (sic), USA.   You're not going to produce analytical grade reagents yourself by this method.

OK.  See, my reference to wikipedia offers two methods -- Zn metal reacted with I2, either in water or ether.  Those methods remove all ambiguity.  Still will only be as pure as your reagents.  I can make no guarantees to fitness for purpose.

[AmateurGuy]

You have an unexpectedly good sense of humor about answering chem questions

Simply put, I wouldn't do it your way.  Yes, by manipulating the concentration and temperature, you get the least soluble of them all to precipitate, and the most soluble of the four reagents still in solution.  But the product, even if gently rinsed with water is still likely very contaminated with the others.

Yeah, although I realize it's not entirely efficient (perhaps my yield expectations should be downgraded), the idea was that I could achieve large quantities of product *cheaply*.  We're talking about a doctoral student's thesis research, done in a home lab.  We already had the zinc sulfate for other purposes anyways, and potassium iodide isn't terribly expensive.  Synthesis from zinc and elemental iodine is the most well known synth, but iodine is actually a DEA regulated chem... not to mention nearly a dollar a gram, compared to less than a dollar per 10g for my method.  People in the citizen chemist forum feel my pain of watching the prices of our reagents so carefully  

I don't have a reference handy for the solubility of each of the four in ethanol, so I can't be sure how well you can rinse impurities away.  Some online references may be able to help you better.

Yeah, that was a big part of what I was looking for, especially with regards to zinc iodide.  The others I have some information on, and they're pretty insoluble.  Zinc sulfate is the most concerning, at 2g/100ml@20.  Zinc iodide definitely seems to be much more soluble than that, however, and if I used the minimum possible I could ideally end up with very little contamination (not 99.9%, but hopefully at least 98.5%).  Unfortunately I can't seem to find anything online... if anyone happens to have advice on their special brand of google-fu, I'm a willing and ready student.

But you're not using lab grade ethanol -- you mention denatured ethanol, as if it were only one formulation, there are many, with different properties.

I believe the stuff I'm using is ~4% methanol, ~96% ethanol, and then some adversive agent like denatonium benzoate or saccharide maybe.

And then Everclear^TM -- beverage-grade ethanol, which isn't really pure, just guaranteed non-toxic, it contains a small, and random, quantity of water.

The stuff on the shelves at the local gas station claims to be 151 proof, which is only 75.5% ethanol, although, as you point out, the exact percentages probably aren't precise... but it's a moot point anyways with that amount of water.  As part of my original question, I was curious how large an effect the remaining water would have on the solubility properties.  I'm guessing something like that is probably pretty tricky, and would require knowing the precise quantities involved...  or maybe even indeterminable?  I couldn't find much on that particular topic (solubility properties in mixed solvents), but then again, perhaps my Google-fu just isn't up to par

Furthermore, you want to buy a beverage, and pay the liquor tax for drinking it, and then not drink it.  No one in industry does that.  No school teaches that.  I don't know about that.  No one does.  Years from now, someone will Goggle this post and offer an opinion, but his mailing address will likely be Toothless Joe, Prospector, Behind the third big rock, Unimproved trritory (sic), USA.  You're not going to produce analytical grade reagents yourself by this method.

Haha, a single bottle of Everclear is a relatively small investment.  Besides, any excess can be used for some delish Coq au Everclear.  But really, if the water content isn't a big deal Everclear is actually cheaper than ordering some non-denatured ethanol intended for lab use.

OK.  See, my reference to wikipedia offers two methods -- Zn metal reacted with I2, either in water or ether.  Those methods remove all ambiguity.  Still will only be as pure as your reagents.  I can make no guarantees to fitness for purpose.

Even if I2 wasn't DEA regulated, it would still probably be nearing the point where just straight ordering zinc iodide@ ~$1/g would be more economical.  When you consider that we are going through perhaps 750g or more, and that this is for writing a paper... you can see how cheaper alternatives become attractive.

Maybe this should be moved to the citizen chemist forum, where this type of non-traditional synthesis and cost motivated chemistry would be more at home than in a school setting.  How would I go about getting a thread moved?

[Arkcon]

You have an unexpectedly good sense of humor about answering chem questions

Thank you for bearing with me so well.

Sorry, I forget that iodine is controlled.  Ether is likewise a little difficult to get for similar reasons.  See, when I need some for oligonucleotide synthesis, I just order some, I have a justifiable purpose, and the stockroom deals with the regulations.  I just don't think any other way -- anything worth doing is worth doing well, anything I can't do well, I won't try.

Okay, so, what you want to do is repeated fractional crystallization, to get the purity up to adequate for your needs.  That's simplest.  It may help that you can use ethanol, of whatever purity you can find, to get some things to precip better.  A good reference is The Concise Chemical Dictionary -- its a little bit easier to find in a public library than a CRC.

Maybe this should be moved to the citizen chemist forum, where this type of non-traditional synthesis and cost motivated chemistry would be more at home than in a school setting.  How would I go about getting a thread moved

The mods may move this thread, but usually, once you've had so many responses, the thread stays where it is.

[billnotgatez]

AmateurGuy -

Was I supposed to have noticed something on those pages?

I was just adding some info to help with the discussion
Can we assume you looked up items you are using on the MSDS and other product resources?

Maybe this should be moved to the citizen chemist forum, where this type of non-traditional synthesis and cost motivated chemistry would be more at home than in a school setting.  How would I go about getting a thread moved?

I am a moderator for citizen chemistry forum
I would be delighted to move this thread - message me or post here

PS
using drinkable ethanol that you pay tax on does grate on some people 

[AmateurGuy]

Sorry, I forget that iodine is controlled.  Ether is likewise a little difficult to get for similar reasons.

Fortunately, ether can be made easily enough from distillation of starter fluid, or synthesized 

For that matter, I suppose I could have reacted my potassium iodide with copper sulfate to isolate the iodine, and then reacted that with zinc metal.

But for that route I'd need to make ether, order zinc, incur losses from the copper iodide, etc.

Okay, so, what you want to do is repeated fractional crystallization, to get the purity up to adequate for your needs.  That's simplest.  It may help that you can use ethanol, of whatever purity you can find, to get some things to precip better.  A good reference is The Concise Chemical Dictionary -- its a little bit easier to find in a public library than a CRC.

Excellent, I'll see if I can hunt down that book.  Thanks for bearing with me as well 

Can we assume you looked up items you are using on the MSDS and other product resources?

Indeed, and I was still stumped as to the solubility properties of zinc iodide in ethanol.

I am a moderator for citizen chemistry forum
I would be delighted to move this thread - message me or post here

Thanks!  I think Arkcon's resource is likely to provide me with a good method, but I'd still be curious if anyone has additional input on ZnI2 solubility in ethanol, sources of information on solubility in mixed solvents, if anyone happens to know much about coagulant action, etc.

If it wouldn't hurt anything, I'd appreciate it.  It's always interesting to see new points of view as well.

PS
using drinkable ethanol that you pay tax on does grate on some people 

Haha.  I've never tried drinking ethanol in my life, I just think of it as another source.  Maybe if I try drinking I'll begin to see the travesty of it 

[AmateurGuy]

Sorry for the double post.

I think I just realized a crazy possibility.  I was looking up the MSDS for my brand of shellac thinner, and couldn't find anything resembling a sulfur compound as an additive.  The smell I got from my ZnI2 was definitely a sulfur type smell... so where could it have come from?

So I was thinking maybe trace amounts of water and ZnI2 are reacting.

ZnI2(aq) + 2H20(l) -> Zn(OH)2(s) + 2HI(aq)

Then, during my soil processing, I use piranha acid to destroy organics before washing it and adding the ZnI2.  Perhaps small amounts of residual H2SO4 are reacting with HI to give H2S.  Some good old hydrogen sulfide would definitely be giving off an unpleasant odor!  As well as possibly stealing eyesight, etc...

I guess I'll have to start adding a slight amount of a weak acid to my heavy liquid to prevent HI formation, and make sure my soil samples are very well washed before I add the heavy liquid...

I suspect I'm well under the ppm limits for any actual risk from the H2S (if thats actually what I'm smelling), but I guess I'll have to start doing all my heavy liquid work in the fume hood...

[vmelkon]

For that matter, I suppose I could have reacted my potassium iodide with copper sulfate to isolate the iodine, and then reacted that with zinc metal.

That's not a good way to do it. Dissolve KI in hot water. Make it concentrated (The less water the better). Add con HCl. You'll have some free floating H- and I- in the solution, think of it as hydroiodic acid. Now add some H2O2 (you can use 3% from the pharmacy). The reaction produces a lot of iodine. See youtube.

When I did it, I didn't get any iodine to precipitate so I had to distill it out. It was a very time consuming process.

Why can't you react dry zinc and iodine? Why does it need water or ether?

[AmateurGuy]

That's not a good way to do it. Dissolve KI in hot water. Make it concentrated (The less water the better). Add con HCl. You'll have some free floating H- and I- in the solution, think of it as hydroiodic acid. Now add some H2O2 (you can use 3% from the pharmacy). The reaction produces a lot of iodine. See youtube.

When I did it, I didn't get any iodine to precipitate so I had to distill it out. It was a very time consuming process.

Nice, I'll keep that in mind if I ever need to isolate some iodine.

Why can't you react dry zinc and iodine? Why does it need water or ether?

I've never done that synthesis, but I assume you would generally do something like add the dry zinc and iodine to your reaction container, then add acidified water to catalyze the reaction.  I believe the reaction would proceed too slowly, at least at room temperature, with just the dry materials.

I've never done the ether method either, but Wikipedia says

It can be prepared by the direct reaction of zinc and iodine in refluxing ether.

[DevaDevil]

how about forming it electrochemically?

get 2 zinc electrodes, use copper iodide as electrolyte in water, apply a potential which will cause the copper to deposit and zinc to dissolute (while not yet evolving iodine, so control the potential), and run it until all copper has been exchanged by zinc.


but honestly, I do not see how zinc iodide is so much more expensive (about 2-3 times compared to comparably pure potassium iodide and copper iodide; is it really worth the effort?). What grade are you looking for?

[AmateurGuy]

how about forming it electrochemically?

get 2 zinc electrodes, use copper iodide as electrolyte in water, apply a potential which will cause the copper to deposit and zinc to dissolute (while not yet evolving iodine, so control the potential), and run it until all copper has been exchanged by zinc.

Nice, I might try that out.  If I do would you mind if I pm'd you for a few questions on specifics of the procedure?  I haven't done too much electrochemistry.

but honestly, I do not see how zinc iodide is so much more expensive (about 2-3 times compared to comparably pure potassium iodide and copper iodide; is it really worth the effort?). What grade are you looking for?

I have a bunch of potassium iodide my employer got for $100/kg.  The zinc sulfate was already laying around the lab.  Really, I've already got a bunch of zinc iodide with sulfate contamination, and I'm just working on removing the sulfates

The ethanol method seems to be working quite well, although fractional recrystallization takes a while and incurs fairly significant losses (at least the way I'm doing it, which probably isn't quite right).

I'm thankful for all the useful alternative routes that have been posted, but at this point I'm likely to continue with this method simply for the sake of education and experimentation if nothing else.  It's always fun for me to do things in a slightly different way than they're normally done