Sciencemadness Discussion Board

Drying wet acetic acid.

Furch - 8-10-2006 at 17:07

Greetings all,

I've got a bottle of presumably wet acetic acid, and I need glacial ditto... I assume it has a concentration of about 90% or higher (I haven't titrated it yet).

One way to go about the problem is to perform an azeotropic distillation, but I can't do that.

Now, if I would've had some Ac2O, I could've made AcO from the water in the solution... But I don't have any Ac2O, so I can't do that either.

What I do have, on the other hand, is SOCl2 (thionyl chloride). As we all know, SOCl2 reacts more or less violent with water, forming HCl and SO2, which are poisonous gases... That's not a problem for me however.

The above mentioned method would rid the solution from water, and leave more or less no trace behind, as the products of the reaction are gasses... However before I start to fuck the whole thing up, I would like someone elses thoughts on the subject. So what do you say? Is this a feasible method to rid water from water contaminated acetic acid? My worst fear is that the reaction is too violent, and that it can't be done for that reason...

Thanks in advance!


- Furch

evil_lurker - 8-10-2006 at 17:23

IIRC if you have 10% water contamination you can distill approx 20% of the volume off and get pure glacial... the azeotrope will come off first leaving pure glacial behind.

This only works with high concentrations of acid though.

Magpie - 8-10-2006 at 19:37

Furch...please do not waste SOCl2 on cleaning up acetic acid. If I had SOCl2 I'd probably be having an orgasm right now. You can always buy glacial at the photo shops.

Secondly, I'm sorry Evil Lurker, but there is no azeotrope. Gmehling's 50 odd citations say so. Please see thread "acetic acid/sodium hydroxide" by Hermes T.

Furch, also please see the above thread. I struggled like crazy just to get 92.5% acetic acid from 87% acetic acid using 2 fractional distillations. I did this just to see what was possible with my equipment.

12AX7 - 8-10-2006 at 19:58

I heard the azeotrope was 96% H2O, and that it's certainly possible to get the AcOH out by distillation, but the boiling and vapor (analog of solidus and liquidus respectively) temperatures are so close that it's very impractical.

Tim

S.C. Wack - 8-10-2006 at 23:13

Furch, why not just do it on a small scale and find out? If we tell you not to, that it will never work, will you believe us and never try it?

It is true that azeotropic distillation is used as a good way to get GAA, but the not-water part of the azeotrope is some added component, not acetic acid. There is no need to get into not-SOCl2 here, there are many acetic acid threads. I'm not sure how many exactly we need. It's all been gone over already, see? A Google search of two acetate addition compound patents that I was aware of brought up this thread. I suggest reading leu's patents at espacenet.

YT2095 - 9-10-2006 at 02:17

I`m not certain, but I beleive the addition of P4O10, should lock up the excess water quite nicely.

Nerro - 9-10-2006 at 02:46

Just curious, would anhydrous CuSO4 or MgSO4 do the job?

YT2095 - 9-10-2006 at 03:22

MgSO4.7H2O loses 6 water at roughly 150c the copper salt even lower temp.

so it could be tricky as Ethanoic acid has a BP of 118c.

Nerro - 9-10-2006 at 03:58

I really don't see why... You heat blue CuSO4.5H2O untill it's white, and then you add it to the glacial-to-be AA.

The salt absorbs the present watermolecules and you filter to remove the hydrate...

Furch - 9-10-2006 at 04:30

Hello again, and thanks for all the replies.

The reason I asked was because I wasn't sure on how SOCl2 will react with water... Sure, it fumes when exposed to the humidity of air, but that doesn't say much about how it will react when the two liquids are mixed. I thought maybe you could provide me with that information.

Anyway, I will titrate my wet acetic acid and then perform the SOCl2 + H2O reaction and report the results back to you, partly for the sake of closing this thread (as there seem to be a lot of AA related threads).

Thanks again!


- Furch

scientistfromdarkness - 9-10-2006 at 04:52

use molecular sieve

YT2095 - 9-10-2006 at 05:01

but isn`t copper sulphate somewhat soluble in AA? I know it is a little in EtOH.
it`s something like the second step in TACC synthing IIRC.

gsd - 9-10-2006 at 07:11

Acetic Acid and Water do not form an azeotrope.

The reason why industrially "Azeotropic Distillation " (with Benzene as an entrainer) is used to separate them is their "relative volatility" is very low. Which means to make glacial AA you would need large number of contacting stages - i.e. very tall column and very high reflux ratio -i.e. very high energy input. Hence when an entrainer like benzene is used eventhough it means 2 distillation columns the over-all fixed as well as operating cost is significantly lower.

gsd

[Edited on 9-10-2006 by gsd]

Nicodem - 9-10-2006 at 07:52

Using SOCl2 to dry acetic acid is not only pretty stupid considering how precious SOCl2 is, but is also very difficult. You would first have to measure the H2O concentration to calculate how much SOCl2 you need. If you add too much you will form acetic anhydride as well. Next, you would have to remove SO2 and HCl from the so dried acetic acid, which is nearly impossible by easy means. SO2 may be removed to some extent by vacuum, but HCl will stay in solution. One way would be to use anhydrous AcONa and then distill, but what a waste of time and precious chemicals just to get something so cheap like acetic acid!

Edit:
And consider that you would need almost 700g of SOCl2 to dry just one liter of 90% acetic acid!

[Edited on 9-10-2006 by Nicodem]

unionised - 9-10-2006 at 10:27

What?
Nobody mentioned freezing out the bulk of the acid, pouring off the water/ acid mix then re melting the purified acid. (Of course, you can always distill the wet acid that you pour off).

I'm pretty sure that someone here would gladly swap a litre of GAA for 700 ml of SOCl2.

YT2095 - 9-10-2006 at 10:33

ok, I`ll bite *sigh* What is so special about this SOCl2?

Furch - 9-10-2006 at 11:31

To me SOCl2 isn't that exotic... You see, what I _need_ is GAA, not SOCl2, hence I'm not stupid for that reason. I would've been stupid if I needed AcOH and somehow spent it to acquire SOCl2, which I don't need. Makes sense, eh?

Moving on: I titrated my presumably wet acetic acid, and came to the conclusion that it's still of high enough concentration (18.5 mol/L) to be used for my purposes.

Anyway, thanks for the replies folks... You were great.


- Furch

Sandmeyer - 9-10-2006 at 16:00

Quote:
Originally posted by Furch
To me SOCl2 isn't that exotic... You see, what I _need_ is GAA, not SOCl2, hence I'm not stupid for that reason. I would've been stupid if I needed AcOH and somehow spent it to acquire SOCl2, which I don't need. Makes sense, eh?


Anyone who can obtain thionyl chloride can also get glacial acetic acid, it's strange that you can't, which raises the question how the hell you got your hands on SOCl2 in the first place. One who thinks that this is a good idea shouldn't mess around with large quantities of chemicals as dangerous and nasty as thionyl chloride, esp since operations with it easily get out of control.
Quote:
One way to go about the problem is to perform an azeotropic distillation, but I can't do that.

As we all know, SOCl2 reacts more or less violent with water, forming HCl and SO2, which are poisonous gases... That's not a problem for me however.



Let us hope that you won't hurt any innocent people...

[Edited on 10-10-2006 by Sandmeyer]

[Edited on 10-10-2006 by Sandmeyer]

Furch - 9-10-2006 at 16:57

Hello Sandmeyer.

I got rather offended by your post. Usually I don't bother answering people who actually make an effort trying to insult me (I know, I know, you're going to claim that it wasn't your intent etc.), however this time I will.

First of all... In case you didn't notice, I brought this topic up for discussion before even considering starting to experiment with it. So I have no clue as to where you got the idea that I thought of it as a "good idea".

I don't know where you are situated, but in my country thionyl chloride is a lot less restricted than glacial acetic acid. Trust me, I know. You want to know where I got my SOCl2? I bought it from a chemical supplier. The very same chemical supplier that denied me to purchase glacial acetic acid, on the grounds that it is restricted for individuals to posess it without a special permit from the authorities.

Stop being an ass just because you haven't got your facts straight, Sandmeyer.

Also, stop hurting innocent people.


- Furch

Sandmeyer - 9-10-2006 at 17:17

Sorry if I insulted you, I'm in a pretty bad mood today due to some personal stuff. I just can't belive that you can buy SOCl2 and not acetic acid, it sounds too absurd to be true. If you're gonna work with SOCl2 in appartmant and simillar (not reccomended), be prepared that nearby metal objects can and will rust - it seems inevitable, but trap must be used to prevent this somewhat. Only an asshole will lead these reaction fumes outside - neighbours will definitly notice. It is enough to simply open the flask briefly to stink up the whole room, doing reaction with such amounts is something to avoid, and trap is a must.

[Edited on 10-10-2006 by Sandmeyer]

[Edited on 10-10-2006 by Sandmeyer]

Furch - 9-10-2006 at 17:47

Thanks for the tips, Sandmeyer!

Indeed it is quite odd... I was amazed myself to find AcOH not being OTC here. It's got the same restriction as concentrated sulphuric- and nitric acid...

I work in a more or less well equipped lab with great ventilation... However that's a good point you're making, about the smell and health hazard concerning my neighbours.

Anyway, I've got my GAA now, and I didn't have to use SOCl2 on it, fortunately... Though I might give it a try in the future just for the science of it, on a microscale of course.

You've got my respect, Sandmeyer!


- Furch

bio2 - 9-10-2006 at 19:15

..........One way would be to use anhydrous AcONa and then distill,..............

I can attest to this , however your flask will be severily damaged. Found this out the hard way!


............. but what a waste of time and precious chemicals just to get something so cheap like acetic acid!..............

Last I checked was $5.40/liter by the jug for the RA, ACS, Glacial Acid.

.................. in my country thionyl chloride is a lot less restricted than glacial acetic acid. Trust me, I know..............

Strange laws, I quess, in some countries these days!

................... you can buy SOCl2 and not acetic acid, it sounds too absurd to be true....................

Yes, it does. Even high purity CH3COOH is like water availability in the chemical industry.

day2knight - 9-10-2006 at 19:54

HI all,

I once left a glass of vinegar in a hot room for 2 months. After that time i got some crystals at the bottom.

KingKarloff - 9-10-2006 at 22:31

Quote:
Originally posted by scientistfromdarkness
use molecular sieve


:o

What Molecular sieve will seperate Acetic acid and water?

[Edited on 10-10-2006 by KingKarloff]

[Edited on 10-10-2006 by KingKarloff]

not_important - 9-10-2006 at 23:01

Quote:
Originally posted by bio2


............. but what a waste of time and precious chemicals just to get something so cheap like acetic acid!..............

Last I checked was $5.40/liter by the jug for the RA, ACS, Glacial Acid.

.................. in my country thionyl chloride is a lot less restricted than glacial acetic acid. Trust me, I know..............

Strange laws, I quess, in some countries these days!

................... you can buy SOCl2 and not acetic acid, it sounds too absurd to be true....................

Yes, it does. Even high purity CH3COOH is like water availability in the chemical industry.


Note that in Forensic Investigation of Clandestine Laboratories (Donnell R. Christian) acetic acid is tagged with "No legitimate home or hobby use". Given recent changes in laws in the US, and Iraq becoming a double plus ungood War to win voters with, expect the WoD to heat up and do not be surprised if possesing or attempting to obtain chemicals so flagged will win you a trip to places you'd rather not go.

YT2095 - 10-10-2006 at 03:37

Quote:
Originally posted by not_important

Note that in Forensic Investigation of Clandestine Laboratories (Donnell R. Christian) acetic acid is tagged with "No legitimate home or hobby use".


well that`s just Pathetic! I use mine for my chili sauce (and could prove it), in fact I bought it Specificaly for that purpose.
so That shoots That arg right up the a$$.

damn these "know it all, know not a lot" do gooders:mad:

Magpie - 10-10-2006 at 10:09

Quote:

Note that in Forensic Investigation of Clandestine Laboratories (Donnell R. Christian) acetic acid is tagged with "No legitimate home or hobby use".


I don't see how Christian can say this. Isn't black & white photography a legitimate hobby? Then again if you are being paid by the Feds to publish a study you will say whatever they want you to say.

Nicodem - 10-10-2006 at 10:27

Quote:
Originally posted by Furch
I don't know where you are situated, but in my country thionyl chloride is a lot less restricted than glacial acetic acid. Trust me, I know. You want to know where I got my SOCl2? I bought it from a chemical supplier. The very same chemical supplier that denied me to purchase glacial acetic acid, on the grounds that it is restricted for individuals to posess it without a special permit from the authorities.

You really should have a talk with your supplier, since I'm quite sure he mixed up something. Where I live one needs to sign all kind of stupid forms when ordering SOCl2 and then wait for a couple of months for the papers being processed and the chemical delivered. This is because SOCl2 is put on several lists of regulation due to atmospheric and environmental hazards it posses. Acetic acid is one of the commonest solvents in chemistry and it takes only a couple of days for delivery and no paper work whatsover. Actually, one can even buy it in pharmacies.
Anyway, it is simply stupid to use SOCl2, not only because of the price difference and self poisoning risks, but like I already said, also because it is impossible to get dry acetic acid by it. You would always get a pretty concentrated solution of HCl in acetic acid contaminated also with acetic anhydride and SO2. The anhydride can be removed by distillation, but the HCl not. It would even be way more wise to use phosphorous(V) oxide.

bio2 - 10-10-2006 at 10:40

...."No legitimate home or hobby use".........

LOL, guess this lead acetate is illegitimate then.

Furch - 10-10-2006 at 16:16

Alright folks... Thanks for contributing. This thread is closed for my part.

- Furch

not_important - 10-10-2006 at 18:48

Quote:
Originally posted by Magpie

I don't see how Christian can say this. Isn't black & white photography a legitimate hobby? Then again if you are being paid by the Feds to publish a study you will say whatever they want you to say.


There you have it - a government picks an enemy to overcome, one where emotional response will be easy to elicit in some of the public, then produces documentation as to how evil the enemy is and why it must be fought. Anything contradicting the (forgone) conclusions will be ignored, discredited, or those expressing the views will be described as mislead and out of touch with current situation. Questionable to bogus statistics will be given as the fight 'progresses'.

I have an aquaIntance in the US who does B&W prints, often using older chemistries. It became difficult to get pyrogall but they found a work-around to obtain it. But their local photosupply store stopped carrying acetic acid, only had pre-mixed stuff. When she tried to order GAA, she was informed that she as an individual or small business could not buy it for reasons very much like those in FICL; the supplier didn't want the trouble of tracking to keep the Federal government happy and local or regional laws were even more trouble.

So that is one reason people try to make GAA from vinegar or air oxidation of home brewed ethanol.

bio2 - 13-10-2006 at 01:30

So what is the best way to remove water from Acetic Acid that is near concentrated.

Ullmans mentions urea but no further info or references are given.

Carbamide doesn't form a hydrate but forms an acetyl among many other compounds. Anyone familiar with this?

jack-sparrow - 13-10-2006 at 04:32

Actualy I am distilling 6 kg of little wet acetic acid (1-2 % water). I distill the crude over 6 feet fractionating column filled with glass helices. The water come out first. You distill until the temperature at the still head is not 115 degC. I assume one can make such a distillation column with a PVC pipe filled with broken glass (or glass beads).

Anyway, my column contains approx. 30-40 theoretical plates. I think you need ca. 20 theoretical plates to separates two component with a 15 degC difference.

gsd - 13-10-2006 at 05:16

Quote:
Originally posted by bio2
So what is the best way to remove water from Acetic Acid that is near concentrated.



I think the best way to remove water from 95+ pure AA is to add Acetic Anhydride to it. ( 100 % Acetic Anhydride = 117 % AA)

This may not be feasible for home/hobby chemist due to lack of availability of AAn. However industrially it is the best option.

gsd

jack-sparrow - 13-10-2006 at 08:20

gsd : you are right !

I just proposed the distillation method because that is the one that I use. I am preparing 6 kg of acetic acid-d4 (deuterated) and acetic anhydride-d6 is just too expensive.

Newbies :

DO NOT prepare glacial acetic acid from scratch with pure acetic anhydride (which is a controlled substance) and water because :

1- You start with 2 phases
2- The reaction is exothermic
3- when the reaction starts, the produced aa increase the solubility at the phases interface and cause with the ongoing exotherm a drastic rise in the reaction rate.
4- boom

Use acetic anhydride to remove a LITTLE (5-10 % max) water in acetic acid.

bio2 - 13-10-2006 at 20:42

This is the excerpt from Ullmans I mentioned.

"A way to obtain pure acid is to add urea or potassium acetate to the acid. Then, glacial acetic acid can be distilled."

The Na or K acetate method is well known however the use of urea deosn;t seem well documented. At least I have been unable to find any further information or details of the process.

Urea being readily available infor cheap in a pure state may have some advantages depending on how much water can be feasibily removed.

S.C. Wack - 14-10-2006 at 01:48

*bangs head against wall*

bio2 - 14-10-2006 at 02:17

You may stop banging now, LOL.

Search and yea shall find.

......Abstract of GB312173

"312,173. I. G. Farbenindustrie Akt.- Ges. May 18, 1928, [Convention date]. Right to Patent relinquished. Acetic acid is obtained from its aqueous solutions by first partially concentrating (to about 60 per cent) and then adding a substance, such as urea or other amide, p-toluidine, or an alkali acetate, which forms an addition compound with acetic acid, removing the remaining water by distillation or crystallization, and then decomposing the addition compound by heating to obtain the acid. The preliminary concentration is effected by cooling to -26 C. while stirring, precautions being taken to avoid supercooling, for which purpose ice crystals may be added. The ice crystals are separated, and may be washed or pressed to recover adhering acid. In the examples, (1) acetic acid of 20 per cent is run into acetic acid of 60 per cent, with stirring, at -26 C., the ice crystals being washed with 20 per cent acid; the 60 per cent acid thus obtained is treated with urea and cooled, with stirring, to about 0 C. and below: the addition compound is separated centrifugally at -17 C. and the acid is recovered by heating in a vacuum, the urea being then dissolved in the mother-liquor, concentrated until the solution contains acetic acid of 60 per cent, and used in the next operation; (2) acetic is concentrated to 60 per cent as above, the ice crystals being pressed to recover the adhering acid, leaving a solid block of ice; anhydrous potassium acetate is added to the 60 per cent acid and the mixture is cooled to -24 C. with stirring; potassium acid acetate with 2 molecules of acetic acid separates, and is heated in a vacuum to recover the acid; the mother-liguor contains potassium acetate and 38 per cent acid, and is returned to the process for the production of 60 per cent acid."...........

bio2 - 15-10-2006 at 18:25

OK, here is the jist of it leaving out all the freezing eutectics etc
which are not really necessary as I see it. Think I've found my way to convert the fractionated 80-90% acid that is piling up
into GAA simply. The unreacted portionwhich is now dilute can then be refractionated.

The K Acetate method is similar except less user friendly as requires cooling to -24 to crystallize out the addition compound.

This is my paraphrased excerpt from the pertinent part of the experimental. Starting with 60% minimum acid.

>>>>>>>> 150 parts urea added to 500 parts 60% acetic acid. On cooling to 0deg CO(HN2)2.2CH3COOH precipitates.
271 parts salt are obtained which when distilled in vauum yield 177 parts GAA. .>>>>>>>>>>>>>>>>

Well boys, what do you think??

Magpie - 15-10-2006 at 19:19

It's easy enough to make 60% acetic with H2SO4 or even HCl. I think what you have paraphrased is worth a try. I'm a little concerned with the need for centrifugation to isolate the crystals. I do have a small centrifuge, however. ;)

bio2 - 15-10-2006 at 22:00

Vacuum filtering quickly at 0 deg then placing a rubber glove or plastic bag over the buchner and letting it press down with the pump running at full vacuum for a while should work just fine.

If more drying is needed the crystals can be washed on the filter with a dry solvent that is miscible with water then placed in a vac dessicator with the pump running till they are dry.

Centrifuging would be faster and easier if available.

not_important - 16-10-2006 at 02:04

You may want to use a plastic bottle or jug to make an ice jacket for the Buchner, seeing as the method says -17 C and lower. Good one to run out of doors in winter.

garage chemist - 16-10-2006 at 04:08

In industry they centrifuge a lot of things which can be filtered on a buchner funnel when working in laboratory scale.
Generally, a buchner funnel (or sintered glass filter) can be used nearly always when a centrifuge is called for. You just have to squeeze out the crystals with e.g. the bottom of a beaker in order to remove the mother liquor.
Of course you need a filtering flask and a vacuum source (aspirator works fine).

[Edited on 16-10-2006 by garage chemist]

bio2 - 16-10-2006 at 08:32

....method says -17 C and lower.....

It also says at 0 deg "nice crystals are obtained.. Based on this the eutectic point should not be required with perhaps some yield decrease. Just have to try it who will be the first?
Will be some weeks before I have the time


The eutectic point is -17 which is not obtainable by simple (ice/salt) bath and complicates the whole procedure. The jacket idea is a good one with the ice salt about -5 to -10 is practically obtained.

Magpie - 16-10-2006 at 10:05

My kitchen freezer comes down to -26C when turned up to max cooling. But keeping everything cold once you remove it is another matter.

I have some 60% acetic acid but no urea. And I don't want to have to buy a 50lb bag to get some. So it will be awhile also for me before trying this.

bio2 - 16-10-2006 at 18:19

... I don't want to have to buy a 50lb bag to get some. ........

The agricultural grade might be only $10 for
this much. Then recrystalize it.