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maozim
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Glacial Acetic Acid synthesis wo sulfuric
What a funny situation!
I need glacial acetic acid. While souricing it is easy, I would like to not wait for UPS ground.
I have access to a kodac stop bath which is like 90% with an indicator dye, but no sulfuric on hand to hydrolyse the sodium acetate. Any azeptropic
distilation possable? I have other chemicals around.
Is hydrolysis of acetic anhydride feasable? Seems blasphemous! But this is time sensitive, as I am leaving for a while and want to finish up
brominating an organic before I leave.
EDIT: in place of sulfuric will clear fuming nitric work?
Thanks in advance.
[Edited on 15-12-2009 by maozim]
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entropy51
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| Quote: | | But this is time sensitive, as I am leaving for a while and want to finish up brominating an organic before I leave. |
You didn't say what you're brominating, but 90% stop bath will work as solvent for some brominations. Just distill to
leave the bromthymol blue behind before using it. It's possible to azeotrope off the water with EtOAc. I wouldn't use HNO3 with NaOAc, I think it
will just make a mess. And I sure wouldn't waste Ac2O on it, although the correct amount added to the 90% would bring it up to near glacial.
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maozim
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Will the acetic that comes through (via distilation through a vigreux) still be the same percentage? Is it a semi-random mix only determinable by bp?
Edit: Bp of 105
[Edited on 17-12-2009 by maozim]
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kclo4
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It is not random, but you'll have to find a table and some references to find what the acetic acid/water azeotrope is...
There might be some possibility of drying the acetic acid with anhydrous magnesium sulfate, or other desiccant. Sodium sulfate, when anhydrous is also
a nice desiccant, but it will likely, as will the Mg sulfate dissolve to some extent and for it to be really pure, need distillation... I would look
into this as it seems the most simple.
Also, perhaps it can be purified by freezing out the acetic acid?
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maozim
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I could pick up sodium sulfate in the morning, and have dry magnesium sulfate on hand.
Perhaps adding enough acetic anhydride to react with some of the water and then drying salts followed by another distilation?
The substrate to be brominated is pretty valuable to me, as I just went through a lithium alluminum hydride reduction to get it.
2-ethoxy-5-methoxyphenylnitropropene, a gift, was the substance reduced.
[Edited on 17-12-2009 by maozim]
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entropy51
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| Quote: | | There might be some possibility of drying the acetic acid with anhydrous magnesium sulfate, or other desiccant. Sodium sulfate, when anhydrous is also
a nice desiccant, but it will likely, as will the Mg sulfate dissolve to some extent and for it to be really pure, need distillation... I would look
into this as it seems the most simple. |
My experience is that AcOH is not easily dehydrated with the usual
drying agents, or by fractional distillation. But others may be able to do better.
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maozim
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Copper sulfate is a recommended drying agent. I am not sure if it is around, I am looking into uses. Since I can't find sulfuic I am unsure if I
can go that way.
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maozim
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Once/if I add acetic anhydride to the distilled acetic solution (which is really coming at 106, I had to stand on my tippy toes to read it correctly),
how long and how much heat will it take to hydrolyse it into acetic? I don't want to acetylate the amine!
Does anyone have access to a table that indicates the %h20 of an acetic solutions boiling at 106 C at sea level?
Ok, so I add a less than stoiciometric amount of acetic anhydride to the distilled solution, reflux to hydrolyse most of the water, add some drying
agent, and distil?
Edit: it looks like copper sulfate is root killer at stores here so that will be the drying agent. I might be able to omit the acetic anhydride
hydrolysis, although it sounds fun 
Would the azeotropic distilation with ethyl acetate be easier? Acetic anhydride is not expensive compared to retail prices for anything!
[Edited on 17-12-2009 by maozim]
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kclo4
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Why even bother adding a drying agent to the mix after you've added the acetic anhydride?
It should do the job... right?
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maozim
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I am not sure how to add exactly enough acetic anhydride so as to not have any excess.
The first fraction was a minimum bp of 106, and the second a minimum of 109, the third is starting at 115.
How in heck can I determine water content like that? Rather than smooth fractions it has been messy. The msds said that it was 80-90%. That is
quite a range!
Acetic anhydride would react with the substrate the solvent is needed for.
Can acetic anhydride be separated from glacial acetic acid by distilation? Can it be turned into something more benign? Something that would not
interfere with the ring bromination of a primary alkylamine salt?
From wikipedia:
Sometimes azeotropes are useful in separating zeotropic mixtures. An example is acetic acid and water, which do not form an azeotrope. Despite this it
is very difficult to separate pure acetic acid (boiling point: 118.1°C) from a solution of acetic acid and water by distillation alone. As
progressive distillations produce solutions with less and less water, each further distillation becomes less effective at removing the remaining
water. Distilling the solution to dry acetic acid is therefore economically impractical. But ethyl acetate forms an azeotrope with water that boils at
70.4°C. By adding ethyl acetate as an entrainer, it is possible to distill away the azeotrope and leave nearly pure acetic acid as the residue.[2]
-----
That sounds pretty easy by comparison! Anyone ever done this?
[Edited on 17-12-2009 by maozim]
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Nicodem
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I'm puzzled by the lack of the thinking process among certain members!
Why on earth do you need to dry a 90% acetic acid if all you need it for is just a solvent for an electrophilic bromination? You could even use water
as solvent, so why do you care about those 10% water?
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Sedit
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| Quote: | | How in heck can I determine water content like that |
...Well...titration of the resulting solution to determine the AcOH content for starters.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Runningbear
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You can buy copper sulphate at the fertilizer section of most big hardware superstores. Not sure on its purity.
Also, apparently if you have 90% Acetic Acid, you can vacuum off most of the remaining water. You need to keep the temp at less than 10C and use
stirring. I haven't tried it though.
Runningbear
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Runningbear
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And I forgot to mention, when you're vacuuming off the water you will know it it works because the acetic acid will begin to form a slushy like mix as
you take our more and more water.
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densest
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The CuSO4 I've seen in hardware stores definitely needs to be recrystallized before use as a reagent. The bottle I have says "95% CuSO4"...
who knows what the other 5% is! Still, crystallizing copper sulfate is easy and the crystals are pretty  I don't have references handy so this may be entirely wrong, but for many salts, if one recrystallized once or twice
then dissolved the purified crystals in distilled water, some organic solvent like an alcohol or acetone mixed into the solution would probably bring
it down as small crystals suitable for heating to an anhydrous state. Large crystals will eventually dehydrate but take a long time. CuSO4 anhydrous
is a moderately strong dehydrating agent in acidic environments. My experience is that it's stronger than MgSO4 (which is more nearly neutral pH) and
can be used where some of the more common agents (CaO, NaOH, etc) are inappropriate.
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Harristotle
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Here is my experience with trying to make a small amount of glacial acetic acid from sodium acetate and NaHSO4.
5 x 50ml sodium acetate handwarmers were obtained and their contents dried for 10h at (200 C) on a frypan. The fluffy salt was collected, ground in a
mortar and pestle, and then stored in an airtight container. 28.8g per 50g handwarmer, or 57.6% was recoverable. (price: $1 per 29g).
40g of this dried NaCH3COO was added to 68g of NaHSO4.H2O (pHDown pool acidifier), and the two powders were ground
together for 5 minutes in a mortar and pestle to achieve intimate mixing.
The whole mass was transferred to a 500ml RBF, then heated on reflux (setting =7, temp data not available but just below the point of baby oil fuming)
in an oilbath for 1.5h.
After 1h, the reaction was cooled, and the rbf was connected to a West condenser, and the mixture heated to distill the product.
Product started coming off at around 100 degrees, rising to 105 degrees. (thermometer is rated to 110).
26ml of product, with a measured density of 1.037 was obtained. CRC/Wikipedia tables reported this to be between 20% and 30%, and by interpolation
between these two values was found to be 28.9% w/w acetic acid.
The actual yield of acetic acid was calulated as 26ml x 1.03 x 0.289 = 7.79g
The percentage yield was calculated as Actual/ moles NaCH3COO x Mr Acetic acid x 100%
which equals 26.5%. 
I thought that this sucked, so I tried to see if I could chase out some more by adding 50ml H2SO4 to the spent residue in the
500mlRBF and distilling that. The still temp never rose above 100 degrees and there was almost no smell of acetic acid in the second distillation.
There was a distinct smell of burnt matches to that second distillation, but not at high concentration.
Conclusion: dry distilling off acetic acid from NaHSO4/NaCH3COO is not viable - a large amount of reagent is used for a terrible
yield. More yield might be achieved by reacting the two as solutions and then double distilling, and I may try this later, if I have time.
It would be interesting to know what happened to the remaining sodium acetate.
Puzzling.
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unionised
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Put the stop bath in the fridge overnight.
Once much of the acid has frozen, pour off the water along with some acid (and a lot of the dye).
Thaw the acid + redistil it.
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clearly_not_atara
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IMHO sodium diacetate not sodium acetate is the better salt for making GAA. It's actually possible to buy flavorings containing sodium diacetate at
grocery stores; it's the primary way to make dry vinegar flavor so any dry vinegar flavoring probably contains it and GAA can be distilled out.
An issue when working with sodium bisulfate and sodium acetate trihydrate is that bisulfate which is not hygoroscopic then deprotonates to
water-loving sodium sulfate, which results in a plaster rxn in the flask:
NaOAc*nH2O + NaHSO4 >> Na2SO4*nH2O + HOAc
However more to the point, phosphoric acid can be obtained by thermal decomposition of fire extinguisher refills if sulfuric acid or bisulfate is
unavailable:
https://www.sciencemadness.org/whisper/viewthread.php?tid=73...
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JJay
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Sodium diacetate looks easy to make too... I might have to give that a try if I need anhydrous acetic acid.
I haven't tried using sodium bisulfate, but I have tried using sulfuric acid and dry sodium acetate in a 1:2 molar ratio, and the yields were
terrible. I don't think the small amount of acid that distilled over was even very dry. The yields when using sulfuric acid in a 1:1 molar ratio
appear to be quite good, but some water ends up in the product unless all of the starting ingredients are absolutely anhydrous.
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Booze
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You really should get sulfuric. It is the easiest way to get glacial acetic acid. Get drain cleaners, in hardware stores. Most brands contain 90%
sulfuric acid, and some go up to as high as 95%.
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Melgar
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Quote: Originally posted by Nicodem  | I'm puzzled by the lack of the thinking process among certain members!
Why on earth do you need to dry a 90% acetic acid if all you need it for is just a solvent for an electrophilic bromination? You could even use water
as solvent, so why do you care about those 10% water? |
Did nobody read this? And has nobody here learned that Nicodem rarely shows up anymore unless someone is saying something incredibly dumb? Judging
from the substrate, OP clearly just wants to make some 2C-B amphetamine derivative, which he does NOT need GAA for. I mean, I guess if someone finds
this thread in the future, some of these suggestions might be helpful (although some of them are way more complicated than necessary) but OP is
probably long gone, on a trip to who knows where.
I'll throw my two cents in though, just because everyone else is: magnesium metal, then decant. It's fast, and I've done it to confirm that it works.
The magnesium will stop reacting when there's no more water left. I can't guarantee there isn't magnesium acetate dissolved in the GAA, but when I
did it, that salt wouldn't have gotten involved in the reaction I was doing so I didn't care.
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JJay
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| Quote: Originally posted by Melgar |
Judging from the substrate, OP clearly just wants to make some 2C-B amphetamine derivative, which he does NOT need GAA for.
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LoL, are you sure about that?? It's just GAA....
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Harristotle
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My application was far more ordinary: I wanted some dry GAA for chromatography purposes.
I searched out a thread where a similar set of processes were being discussed, and, without any deep consideration for other applications posted my
experience, as well described as I could, in the hope that it might be useful to someone.
Why bother with NaHSO4 instead of sulfuric acid? simply because it is a lot more OTC around here
Cheers, H.
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clearly_not_atara
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| Quote: Originally posted by Melgar | | Quote: Originally posted by Nicodem | I'm puzzled by the lack of the thinking process among certain members!
Why on earth do you need to dry a 90% acetic acid if all you need it for is just a solvent for an electrophilic bromination? You could even use water
as solvent, so why do you care about those 10% water? |
Did nobody read this? And has nobody here learned that Nicodem rarely shows up anymore unless someone is saying something incredibly dumb? Judging
from the substrate, OP clearly just wants to make some 2C-B amphetamine derivative, which he does NOT need GAA for. I mean, I guess if someone finds
this thread in the future, some of these suggestions might be helpful (although some of them are way more complicated than necessary) but OP is
probably long gone, on a trip to who knows where. |
I read it, but I think preparing GAA is a topic of general interest. It's one of a relatively few solvents that's easily prepared from materials
available almost everywhere.
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j_sum1
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In case anyone missed it, Nicodem's comment quoted above is eight years old and the immediate context for asking the question is certainly long gone.
I have been following this thread because I recently had the idea of making GAA using NaHSO4. Sulfuric acid is precious to me and I would rather
substitute where I can. (Not that I have any sodium acetate at the moment.)
So far the only definitive statement made on this idea is from harristotle who revived this zombie thread. He claims poor yield but I am not really sure why this should be.
I am not really sure I understand the logic of his suggestion that the reaction happen in solution. My understanding is that distilling acetic acid
from a water solution is problematic and also gives low yields. Please correct me if I am misunderstanding something. Adding water to the reaction
vessel would, at face value, seem to be a step away from obtaining an anhydrous product.
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