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[*] posted on 25-7-2009 at 13:02


I have a solution of 90% acetic acid.

The bps of acetic acid and water only vary by 18deg.C.

I don't necessarily need all of the water out, but it would be nice, and googling "acetic acid distillation" has only sorta helped.

What would be my best be to concentrate the acetic acid?

Thanks!




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[*] posted on 25-7-2009 at 13:09


There are a number of ways you could do it. One would be to react the solution with a base and then acidify the salt with sulfuric or phosphoric acid. This is the method I use, but only because I start with vinegar that is only 4% acetic acid by weight. For you, I would recommend the use of a dessicant such as MgSO4 or CaCl2.



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[*] posted on 25-7-2009 at 14:40


Quote: Originally posted by ammonium isocyanate  
There are a number of ways you could do it. One would be to react the solution with a base and then acidify the salt with sulfuric or phosphoric acid. This is the method I use, but only because I start with vinegar that is only 4% acetic acid by weight. For you, I would recommend the use of a dessicant such as MgSO4 or CaCl2.


How do you do this? Do you add the unhydrous sodium acetate to H2SO4, and then distill?
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[*] posted on 25-7-2009 at 15:33


Quote: Originally posted by manimal  
Quote: Originally posted by ammonium isocyanate  
There are a number of ways you could do it. One would be to react the solution with a base and then acidify the salt with sulfuric or phosphoric acid. This is the method I use, but only because I start with vinegar that is only 4% acetic acid by weight. For you, I would recommend the use of a dessicant such as MgSO4 or CaCl2.


How do you do this? Do you add the unhydrous sodium acetate to H2SO4, and then distill?


You got it. In fact, if you use sulfuric acid you don't need totally anhydrous acetate as the sulfuric acid acts as a dessicant. ;)




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entropy51
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[*] posted on 25-7-2009 at 16:43


Quote: Originally posted by querjek  
I have a solution of 90% acetic acid.

The bps of acetic acid and water only vary by 18deg.C.

I don't necessarily need all of the water out, but it would be nice, and googling "acetic acid distillation" has only sorta helped.

What would be my best be to concentrate the acetic acid?

Thanks!


This is an old problem, and there are threads on it that you should consult.

MgSO4 and CaCl2 won't remove the last of the water from 90% acetic acid. It's very difficult to fractionally distill off the water. Since you're already almost to glacial acid converting to NaOAc and distilling with H2SO4 is fairly wasteful. And the NaOAc does need to be anhydrous, I wish people wouldn't give advice when they're clueless. It doesn't make them look smart to say something when it's obvious that they are just blowing smoke out their arse. Distilling the NaOAc trihydrate with H2SO4 will give approximately the 90% acid you already have.

One way is to add enough EtOAc to form an azeotrope with the water in your 90% acid and distill with a good fractionating column. First the azeotrope will distill at about 70 C, then the EtOAc will come over at about 77 C, and finally glacial AcOH will distill at about 118 C.

But consult the existing threads. Their has been a lot of discussion about this.

In one of those threads, SC Wack posted a promising looking patent in which wet AcOH is frozen in vacuum and the H2O evaporated off leaving crystals of AcOH. It looked workable, but it didn't work for me. I think it should under the right conditions.

[Edited on 26-7-2009 by entropy51]
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[*] posted on 26-7-2009 at 09:55


You could use P4O10 as a dessicant, but that is hard to come by (at least for me).

I have a question of my own. I had a solution of CuSO4 and tried to dispose of it with NaHCO3 and Na2CO3. A volumous greenish precipitate formed. However, a deep blue solution remained, presumably containing cupric cations. I can't think of any reason ammonia or any other chemical would be present that would complex with Cu++ ions. Does HCO3- form any complex with copper? I can't really dispose of this solution until I know it contains no copper ions. Any ideas for precipitating them?




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[*] posted on 27-7-2009 at 11:29


Is it possible to obtain 95% on a Reimer-Tiemann? I was always under the impression that yields of the Reimer-Tiemann are mediocre, yet SciFinder claims that some Chinese claim that they obtained 95% on a modified Reimer-Tiemann (with tertiary amine) on p-methoxyphenol:
Liaoning Shifan Daxue Xuebao, Ziran Kexueban (2007), 30(3), 328-329. (Journal written in Chinese)

Here: http://pubs.acs.org/doi/suppl/10.1021/ol800507m another group of Chinese claims 91% for Et3N, CH3CN, paraformaldehyde.
The base must be a tertiary amine, since other amines would condense with the aldehyde/formaldehyde and give water, right?
And triethanolamine (OTC for me) cannot be used, since the OH groups are too acidic, isn't it?
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[*] posted on 27-7-2009 at 16:55


Quote: Originally posted by turd  
Is it possible to obtain 95% on a Reimer-Tiemann?


Is Chinese borosilicate glass the same as Pyrex?
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[*] posted on 28-7-2009 at 05:46


Quote: Originally posted by ammonium isocyanate  
..I had a solution of CuSO4 and tried to dispose of it with NaHCO3 and Na2CO3. A volumous greenish precipitate formed. However, a deep blue solution remained, presumably containing cupric cations. I can't think of any reason ammonia or any other chemical would be present that would complex with Cu++ ions. Does HCO3- form any complex with copper? I can't really dispose of this solution until I know it contains no copper ions. Any ideas for precipitating them?


The basic copper carbonates, you're not going to see true CuCO3, form soluble complexes with excess carbonate. Try boiling in a wide mouthed container for a quarter hour or so, this may convert all the copper to cupric oxide.

Alternatively let the solution evaporate to dryness.

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[*] posted on 28-7-2009 at 09:12


Indeed, it's better to neutralize a copper solution with sodium hydroxide than carbonate for exactly this reason.

You do run the risk of ammonia impurity and cuprate formation, but those should be controllable with purity and pH.

Boiling, so CuO forms immediately, is always a good idea. Besides precipitating a stable form, it also settles faster and denser.

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[*] posted on 28-7-2009 at 10:48


Hmmm... I guess I'll have to try boiling, as evaporating isn't an option given that I have ~600mL of the solution.

An interesting side-note, I added more carbonate to one batch than the other, and then tried nutralizing that one with vinegar. It is now a more turquoise/light blue color, whereas the other a deeper blue. Addition of alkali halides to the light blue solution (just in case Cu++ ions had been reduced to Cu+ ions) results in the evolution of copious quantaties of gas, predsumably CO2 as no odor was observed, it did not support flame, and did not really affect a pH test strip very much, nor was any smoke-like affect shown, as would be expected from hydrogen halides. No precipitate forms. No reaction is observed with the other solution.

Addition of almunium or magnesium poweder to the dark blue solution results in a single-displacement reaction, yielding what appears to be copper metal and leaving a purple solution behind. No reaction is observed with the light blue solution.




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[*] posted on 28-7-2009 at 12:35


Quote: Originally posted by entropy51  
Quote: Originally posted by turd  
Is it possible to obtain 95% on a Reimer-Tiemann?


Is Chinese borosilicate glass the same as Pyrex?

Why do you post if your intent is not to help?

Scifinder states the reagents as 4-methoxyphenol, CHCl3, EtOH, NaOH and Et3N. My bet is on translation error or nonsense publication. I've seen too many of both lately. :(
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[*] posted on 29-7-2009 at 13:21


What is the best way to dispose of chromate/dichromate compounds? I don't have any soluble lead (II) compounds, so I can't go the lead chromate route.



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[*] posted on 29-7-2009 at 13:52


Quote: Originally posted by ammonium isocyanate  
What is the best way to dispose of chromate/dichromate compounds? I don't have any soluble lead (II) compounds, so I can't go the lead chromate route.


Flood the reaction mixture with sulfites and acid (generate SO2 in-situ), reducing all hexavalent chromium to relatively harmless Cr(III). You may want to heat a bit just to make sure it goes to completion.

[Edited on 7-29-09 by UnintentionalChaos]




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[*] posted on 29-7-2009 at 14:20


PbCrO4 (which occurs as the rare mineral crocoite) is, like PbSO4, only very slightly soluble, which would, if a soluble Pb salt were available, allow it to be used to precipitate Cr(VI) from solution. It, and ZnCrO4 which is more soluble and less toxic, is of use as an intense red paint pigment, especially in anti-corrosive roof paints and metal primers.

[Edited on 30-7-09 by JohnWW]
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[*] posted on 29-7-2009 at 15:39


Quote: Originally posted by turd  
Quote: Originally posted by entropy51  
Quote: Originally posted by turd  
Is it possible to obtain 95% on a Reimer-Tiemann?


Is Chinese borosilicate glass the same as Pyrex?

Why do you post if your intent is not to help?

Scifinder states the reagents as 4-methoxyphenol, CHCl3, EtOH, NaOH and Et3N. My bet is on translation error or nonsense publication. I've seen too many of both lately. :(


The answer to both questions is no, obviously. Your inference of my intent was wrong, meadow muffin.
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[*] posted on 29-7-2009 at 16:23


Quote: Originally posted by JohnWW  
PbCrO4 (which occurs as the rare mineral crocoite) is, like PbSO4, only very slightly soluble, and could be used to precipitate Cr(VI) from solution. It, and ZnCrO4 which is more soluble, is of use as an intense red paint pigment, especially in anti-corrosive roof paints and primers.


1) he explicitly stated that he can't use lead as a precipitant.
2) must you include a wikipedia-like rundown of useless trivia with every post?




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[*] posted on 29-7-2009 at 19:04


Quote: Originally posted by ammonium isocyanate  
What is the best way to dispose of chromate/dichromate compounds? I don't have any soluble lead (II) compounds, so I can't go the lead chromate route.

I make the solution acidic, then use an alcohol or even sugar and heat to reduce most of the Cr(VI) to Cr(III). Finish off with a little bisulfite or sulfite+extra acid, then precipitate the Cr(III) for recovery.

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[*] posted on 29-7-2009 at 21:20


Thanks for the advice, but I ended up figuring out how to dispose of it. I dissolved the ammonium dichromate in water, acidified with NaHSO4, reduced with aluminium powder, and added KOH to make sulfate anions and precipitate the chromium (III) ions.



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[*] posted on 30-7-2009 at 01:28


A small question,

How should I store pure lithium metal?
I can imagine it is stored under oil as potassium/sodium would be stored.
Or would an airtight container suffice.




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[*] posted on 30-7-2009 at 03:44


Airtight container would have to be purged of all moisture/oxygen. So under mineral oil would probably be best .



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[*] posted on 30-7-2009 at 04:44


You can't really store it under oil because it floats to the surface. In order to store it use a piece of plastic wrap stuffed in the container to hold the Lithium Down. I have stored it for sometime this way.

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[*] posted on 30-7-2009 at 14:13


Is it necessary to use teflon tape to seal teflon-to-teflon normal pipe thread connections? I recently acquired a used KNF double teflon diaphragm vacuum pump, and upon taking it apart, I found the previous owners had used teflon tape to seal the threads that hold the valve holders (don't know what they're really called) into the main pump head.

After taking it all apart and cleaning it up I put it back together. It only pulls about 25"Hg in parallel arrangement, while the specs say it should do at least 28". So I'm trying to figure out what the problem is..

[Edited on 30-7-2009 by 497]
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[*] posted on 30-7-2009 at 20:56


Can ice (H2O) be sublimated at -10*C to ~0*C using the vacuumed formed from an aspirator/water jet vacuum?

That is.. in any reasonable time. I'd like to sublimate a small bit (10ml at most!) in a test tube in an attempt to make some SEAgel

The reason I ask is because if it is, it seems like it would allow me to make a small amount (volume wise) of SEAgel in a test tube, which seems way cooler then that aerogel stuff.

http://www.youtube.com/watch?v=HoCAxS4vqwQ

It is made basically by sublimated frozen water that has been gelled by agar.

[Edited on 31-7-2009 by kclo4]




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[*] posted on 30-7-2009 at 21:56


In order to subliminate ice, you need a pressure a little under 1kPa (~1/100 of an atmosphere), which sounds a little low for an aspirator vacuum. At this pressure, ice will subliminate at a few degrees below 0*C.



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