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Author: Subject: Separation of toluene and isobutanol
Mixe
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[*] posted on 29-11-2021 at 11:27


But I'm a bit confused about the sulphuric acid. I've read up ferociously but the information points everywhere: protonated and dehydrated alcohol = ester = even more soluble in toluene = even more problems, but then there's the question of temperature, and if the end product is isobutylene, etc etc ...

As for the solubility in water, would increased temperature favor the washout of isobutanol from toluene to water? If I boil a mixture of water and the mixed solvent?
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DraconicAcid
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[*] posted on 30-11-2021 at 11:42


The acid reacts with the alcohol to give isobutylene, which will evaporate and be lost during the distillation.



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[*] posted on 1-12-2021 at 14:46


Quote: Originally posted by Mixe  
But I'm a bit confused about the sulphuric acid. I've read up ferociously but the information points everywhere: protonated and dehydrated alcohol = ester = even more soluble in toluene = even more problems, but then there's the question of temperature, and if the end product is isobutylene, etc etc ...


It would be easy enough to test with a test tube and less than a minute of shaking...basifying the aqueous layer either releases the alcohol or doesn't (I'd heat to boiling w/NaOH and see what the vapor smells like, after washing w/bisulfite in the first place)...isobutylsulfuric acid would be the product, and I suspect that it's more soluble in the acid.(ethylsulfuric acid is insoluble in ether for instance) (if CaCl2 reacts with the alcohol other than salting it out of aq. solution, it does so in the anhydrous form)

Perhaps some cheap substance can be found which preferentially absorbs a large amount of the more polar cpds...no doubt y'all will get testing and report back...my entry for the grand prize: oxidizer, NaOH, bisulfite.

[Edited on 2-12-2021 by S.C. Wack]




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[*] posted on 2-12-2021 at 02:43


Yes, I will get right into this and report back. I just have to produce some conc H2SO4 first... In my country, its a listed chemical, and the level of control is unbelievable. At this time, for me, the only available source is finding older car batteries and doing the kind of messy work-up from there.
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[*] posted on 2-12-2021 at 12:03


I wouldn't use sulfuric acid from the start, just go for water and CaCl2, maybe you can reflux with sulfuric acid when CaCl2 doesn't work.
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[*] posted on 4-12-2021 at 08:50


It's entirely possible that the alcohol is just as soluble in other mineral acids. Either way, and also before treatment with dry CaCl2 for a length of time, the acetone has to be removed first.

Heating with sulfuric acid would sulfonate toluene and condense acetone long before dehydrating the alcohol; that operation is performed at 160-200C.




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[*] posted on 25-12-2021 at 10:46


Quote: Originally posted by S.C. Wack  
It's entirely possible that the alcohol is just as soluble in other mineral acids. Either way, and also before treatment with dry CaCl2 for a length of time, the acetone has to be removed first.

Heating with sulfuric acid would sulfonate toluene and condense acetone long before dehydrating the alcohol; that operation is performed at 160-200C.


Ok, so what is your practical advice in this case? Of course the aceton is distilled off first, thats easy. Yes, adding sulphuric acid would sulfonate the toluene, I can see that, but that brings us full circle around to the beginning: how to separate isobutanol and toluene? Or if the isobutanol is unchanged by adding sulphuric acid but the toluene is sulfonated, would that be a step closer to separation?

Could one, for example, add sulphoric acid to the mix of isobutanol and toluene, crystallize the toluenesulphonic acid, filter the crystals out, then boil them in water and distill off the hydralized pure toluene?




[Edited on 20212121/12/25 by DocX]
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[*] posted on 25-12-2021 at 13:20


Even if you could hydrolyse the pTsOH efficiently, you would need about a gram of sulfuric acid for every gram of toluene.

I would still first try to extract the alcohol with water and remove the last bit with CaCl2. You can salt the isobutanol from the water with CaCl2 as well.

[Edited on 25-12-2021 by Tsjerk]
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[*] posted on 26-12-2021 at 09:27


Quote: Originally posted by Tsjerk  
Even if you could hydrolyse the pTsOH efficiently, you would need about a gram of sulfuric acid for every gram of toluene.

I would still first try to extract the alcohol with water and remove the last bit with CaCl2. You can salt the isobutanol from the water with CaCl2 as well.

[Edited on 25-12-2021 by Tsjerk]


Yes yes, that is suggested a kazillion times in this thread, and naturally that will be steps 1-4, and fairly obviously so. But if you really really want clean toluene, I'm wondering about that last, definitive step.
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[*] posted on 26-12-2021 at 13:52


I understood you wrong because you suggested adding sulfuric acid to the mix, not to the purified toluene.
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[*] posted on 26-12-2021 at 20:01


If you want the last definitive step for removing all isobutanol from toluene, reflux it over sodium metal before distilling.



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[*] posted on 27-12-2021 at 08:36


A cheap, albeit not greatly effective method, would be to get the reflux a large amount of this mixture with a large amount of anhydrous copper sulfate. This would dehydrate the isobutanol to isobutene, which should escape the solution as the toluene refluxes. https://pubs.acs.org/doi/10.1021/jo01293a030 This won't get rid of it all, but since copper sulfate is so cheap, you can buy it by the kilo for a few bucks, it could be a good starting point in removing the isobutanol, then do some of the more expensive methods listed above



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[*] posted on 27-12-2021 at 13:06


Quote: Originally posted by DraconicAcid  
If you want the last definitive step for removing all isobutanol from toluene, reflux it over sodium metal before distilling.


Now this is interesting! For a n00b like me, what reaction does this provoke?
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[*] posted on 27-12-2021 at 13:46


Quote: Originally posted by DocX  
Quote: Originally posted by DraconicAcid  
If you want the last definitive step for removing all isobutanol from toluene, reflux it over sodium metal before distilling.


Now this is interesting! For a n00b like me, what reaction does this provoke?


The alcohol will be converted to sodium alkoxide, which is non-volatile. Also very good for removing the last traces of water and oxygen.




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[*] posted on 27-12-2021 at 14:49


Quote: Originally posted by DraconicAcid  
Quote: Originally posted by DocX  
Quote: Originally posted by DraconicAcid  
If you want the last definitive step for removing all isobutanol from toluene, reflux it over sodium metal before distilling.


Now this is interesting! For a n00b like me, what reaction does this provoke?


The alcohol will be converted to sodium alkoxide, which is non-volatile. Also very good for removing the last traces of water and oxygen.


Yes, I was able to conclude that by UsingThe Damn Search Engine. Sorry for blurting out questions and thank you for your patient reply. What I haven't been able to really understand from my search results is if the sodium will react in any way with the toluene, and if the reaction with the 5-10% of isobutanol will be violent and risky?
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[*] posted on 27-12-2021 at 15:31


Sodium will not react with toluene or other hydrocarbons (apart from alkynes, possibly)- when I as a grad student, most of our solvents (benzene, toluene, ethers, alkanes) were purified by refluxing over sodium (with a bit of benzophenone) under nitrogen for an hour or two before distillation. The benzophenone was there as an indicator- if it formed the blue radical anion with sodium, you knew it was very dry.

I don't think the reaction with 5-10% isobutanol would be very violent, but I'd dry it with something else first, just be be safe.




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[*] posted on 30-12-2021 at 00:16


This was perfect! Thank you so much. If I pull that off, I have a relatively cheap and readily accessible true OTC source of toluene.
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[*] posted on 8-5-2022 at 04:13


I have the same problem as Mixe, toluene is only available as a toluene-acetone-isobutanol mix in the ratio 70-80/15-20/5-10% respectively.

Acetone is completely miscible with water so that'll be easy, just a sep funnel and some water washings. Any remaining acetone (bp=56 C) will be gone long before anything else starts distilling over. I looked up the boiling points (in C of course) of any possible azeotropes as well as the pure substances:

110.6 Toluene
108.4 Isobutanol
101.2 Toluene/Isobutanol azeotrope 55.5% toluene
100.0 Water
89.7 Isobutanol/water heterogeneous azeotrope 30% water
85.0 Toluene/Water heterogeneous azeotrope, 20.2% water.

The obvious solution is to, as stated before in the thread, just fractionally distill off IBA/toluene followed by only toluene, sacrificing the required amount of toluene to form the 44.4/55.5 IBA/Toluene azeotrope. There is a 9.4 C difference between the azeotrope and toluene.


BUT, if a small amount of water was added instead, would said water all be consumed by forming Toluene/water vapor first, with negligible isobutanol following due to the water vapor "preferring" to form a vapor mix with toluene? The difference in BP isn't big (4.7 C), but if the water runs out....This is as you might've guessed, both a "fundamentals" and a practical question for me, but it's been gnawing at my mind lately and I don't know how to formulate in order to "just google" such a complex question.


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[*] posted on 8-5-2022 at 05:33


Esterify the iBuOH with a high boiling carboxylic acid, e.g. benzoic acid, and use a Dean Stark to remove toluene/water azeotrope. You will get isobutyl benzoate, b.p. 241 (Practical Organic Chemistry, Mann and Saunders, p. 546), so easily separable from toluene by cranking up the heat once you don’t collect anymore water/toluene/iBuOH azeotrope
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[*] posted on 8-5-2022 at 06:52


@Jome: unless you have a very efficient column you would end up distilling a mixture of water/toluene and water/isobutanol, as the 5 degree difference is very small.

So getting clean isobutanol out of the mixture will be hard, but the different azeotropes do make it possible to end up with clean toluene.
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[*] posted on 9-5-2022 at 11:16


I would do some test distillations first and then collect fractions for every 10% of the volume or every few degree change and just see if any are pure. It will not be trivial to separate them completely, but it should be possible to get at least a few fractions of distillate that are mostly one component, then they can be pooled and redistilled again to get nearly pure material. Then I would try to remove the last traces of alcohol or water. Trying to remove bulk water or alcohol with sodium would make a big mess or fire, most likely, but should be easy after one or two distillations. And certainly trapping the isobutyl alcohol as an ester might work, but you might add some acetyl chloride and distill off the isobutyl acetate at 118, which is above the toluene. It might be useful for something.
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