Sciencemadness Discussion Board

Help with azeotrope

sumatra - 14-9-2018 at 11:51

So I bought a laquer-thinner from the hardware store and decided to fractionally distill it. The contents are 55-60% butanol (it says just butanol so I assume its 1-butanol), 16-20% o-xylene and 16-20% methoxypropanol. I started my fractional distillation and liquid started coming over at 80 C. I assume its a xylene-methoxypropanol azeotrope, but I couldn't find any info.
Update: next fraction started distilling at 117 C, I think its a mixture of xylene and butanol (azeotrope boils at 117 and has a toluene-ish odour).



[Edited on 14-9-2018 by sumatra]

[Edited on 14-9-2018 by sumatra]

macckone - 14-9-2018 at 13:32

Tertbutyl alcohol boils at 83C.
Methoxypropanol boils at 120C.
Xylene boils at 137C.
N-Butanol boils at 117.7C
2-Butanol boils at 100C.

The p-xylene - N-butanol azetrope boils at 115-116 depending on source for the data. m-xylene is similar.

This mix is going to be every hard to separate by distillation alone.

I suspect your first fraction is some azeotrope of tertbutyl alcohol.

sumatra - 16-9-2018 at 06:49

Is thеre any accessible test reaction for the tertbutyl alcohol? I know it solidifies at close to room temperature and Ill try it out, although I doubt it'll solidify as an azeotrope.
I still believe that the 80C distillate is an azeotropic mixture of tertbutyl alcohol and o-xylene, I'll attempt breaking the azeotrope by adding water. tertbutyl alcohol and water azeotrope boils at just below 80C, so with careful heat control and with several repetitions I think I may get rid of the xylene.


[Edited on 16-9-2018 by sumatra]

fusso - 16-9-2018 at 07:03

Lucas test?

UC235 - 16-9-2018 at 07:51

I'm pretty sure n-butanol is used as a thinner so it would make sense for it to be here. A good whiff should give it away if it's tert-butanol. tBuOH has a minty-camphoraceous smell. nBuOH is widely disliked among labs that use it.

sumatra - 16-9-2018 at 08:56

Quote: Originally posted by UC235  
I'm pretty sure n-butanol is used as a thinner so it would make sense for it to be here. A good whiff should give it away if it's tert-butanol. tBuOH has a minty-camphoraceous smell. nBuOH is widely disliked among labs that use it.

Oh, well that's good to know. Thank you. No, it does not have a such an odour, it does have an alcoholic odour and a bit of a toluene-ish tinge to it. As far as I know the o-xylene n-butanol azeotrope does not boil at 80 C.

12thealchemist - 16-9-2018 at 09:01

Would the Komarowsky reaction be worth considering here? That, or some other test to distinguish between different alcohol isomers?
www.youtube.com/watch?v=3blWSH7dcE0 (NurdRage video to exemplify)

Elrik - 16-9-2018 at 09:32

n-Butanol [75%] & o-xylene azeotrope boils at 116.8°C, just 1° below n-butanol

Azeotropic Data - Advances in Chemistry [1973]

fusso - 16-9-2018 at 10:19

Quote: Originally posted by UC235  
nBuOH is widely disliked among labs that use it.
Why?

UC235 - 16-9-2018 at 11:03

Quote: Originally posted by fusso  
Quote: Originally posted by UC235  
nBuOH is widely disliked among labs that use it.
Why?


Traces of butyraldehyde make it smell terrible. I've seen it described as alcoholic smelling, tinge of overripe bananas and puke.

sumatra - 29-9-2018 at 09:44

Sorry for not keeping you updated, I'm a med student so I don't have that much time on my hands. I just tested the mixture and it deffinetly does NOT have any tert. butanol.
I came up with this: Since the xylene is imiscible with water, but the methoxypropanol and the butanol are, if I add water to the lacquer-thinner it will hold on to the alcohol and methoxyropanol but the xylene will separate out of the mixture. The lower layer will then be distilled and I should be able to separate the butanol from the methoxypropanol.
I'll update the thread as soon as I find the time to test out my theory, but I'd love to hear your thoughts about it.

[Edited on 29-9-2018 by sumatra]

macckone - 29-9-2018 at 20:57

The solubility of n-butanol in water is low. It will prefer the xylene layer as it is much more soluble in xylene.

sumatra - 29-9-2018 at 21:44

Quote: Originally posted by macckone  
The solubility of n-butanol in water is low. It will prefer the xylene layer as it is much more soluble in xylene.

I was wondering about that, it would make the separation easier though, I will distill the xylene too

sumatra - 30-9-2018 at 01:13

UPDATE: I added water to the lacquer-thinner and obviously 2 layers formed, a lower aqueous layer which was milky-white and a relatively small upper xylene layer. I then proceeded to test the two layers.
First a added 10 ml of water to an eprouvette followed by 10 ml of the thinner, I then mixed them vigorously and allowed the layers to separate. Then I used a syringe to remove only the upper xylene layer which was 2 ml. On the bottle it says that the xylene content is 16-20 %, which means that these 2 ml are in the theoretical percentage, I however proceeded to test both layers with acidified KMnO4 solution. The aqueous layer formed a lot of MnO2 and the upper xylene layer was just faintly coloured. This leads me to think that the butanol prefers staying mixed with the water but a small amount does dissolve in the xylene.
I also tried testing using acidified dichromate, but it turns out that my concentrated sulfuric acid is contaminated and it gave a false positive.
As soon as I find the time I'll distill both layers and update the thread.

sumatra - 30-9-2018 at 07:45

UPDATE:
I ran the distillation of both layers and got interesting results.

Aqueous layer distillation:
The first distillate came over at 78 C and has a sweet alcoholic odour to it, it decolours acidified KMnO4 and I think I faintly smell a puke-ish odour (I'm not sure at all, maybe the alcohol is 2-butanol which oxidizes to a ketone and in turn to propanol and methanol, but I doubt it). I collected this up to 92 C, after which I changed the receiving flask. The temp. steadily rose to 101 C and little distillate came over, after reaching 100 C a lot more distillate started coming over (probably water). This second distillate I collected for quite some time but the temperature didn't rise so I stopped the distillation, the distillate also has a sweet alcoholic odour, although its rather faint (probably because of the water dilution).

Xylene layer distillation:
First distillate again came over at 78 C, but that was the only thing which came over. It still has the same xylene-ish odour to it and the boiling flask had no residue whatsoever. The glassware had some water droplets from the previous run, but I doubt it made a difference.

Okay, so I'm still perplexed. The first 78 C distillate should be the butanol, but the BP is quite low and the xylene one is even more strange. Maybe both compounds formed some kind of azeotrope with the methoxypropanol, but I couldn't find any information online. Suggestions?

Cactuar - 30-9-2018 at 15:21

How does your fractional distillation set up look like? How long is the column and what is it packed with?
Are you sure your thermometer is accurate?
Try diluting an aliquot of the aqueous phase and see if you can get the n-BuOH to separate. They're probably miscible right now because of the PGME.
Try adding NaCl to an aliquot of the aqueos phase and see if you can get the n-BuOH and PGME to separate from the water.

macckone - 30-9-2018 at 22:50

Something is not what you think it is.
The formulation could have changed but the label and MSDS were not updated.
t-butanol is miscible with water.
methoxypropanol would not make n-butanol soluble to the extent described at the ratio listed.

sumatra - 30-9-2018 at 23:45

Quote: Originally posted by Cactuar  
How does your fractional distillation set up look like? How long is the column and what is it packed with?
Are you sure your thermometer is accurate?
Try diluting an aliquot of the aqueous phase and see if you can get the n-BuOH to separate. They're probably miscible right now because of the PGME.
Try adding NaCl to an aliquot of the aqueos phase and see if you can get the n-BuOH and PGME to separate from the water.

I actually did get a third layer while I was diluting yesterday, however I didn't pay much attention to it. I tried to repeat the same thing today, however no third layer formed, I added NaCl, but the result was the same.
I use a Vigreux distillation column 20 cm, yes the thermometer is accurate, I've used it for a lot of reactions which would have failed if it wasn't.

sumatra - 30-9-2018 at 23:54

Quote: Originally posted by macckone  
Something is not what you think it is.
The formulation could have changed but the label and MSDS were not updated.
t-butanol is miscible with water.
methoxypropanol would not make n-butanol soluble to the extent described at the ratio listed.

I tried finding the exact contents of the thinner but the company hasn't listed them.
I think its not t-butanol because I got a positive result when testing with acidified dichromate, unless the methoxypropanol reacts with it.
I've also heard that at higher temp it can decompose to methanol and acetone, but I doubt I've reached such a temp. I did do the iodoform test and got a negative result (or so it seems, the iodine cleared up upon addition of NaOH, but I got no CHI3).
I've been thinking of reacting the butanol with HCl, seperating the chlorobutanol and reacting it with NaOH, but its too much of a hassle, I would mainly use the butanol for esterification, but I think it would work just as good if I use the thinner.

macckone - 1-10-2018 at 06:09

Something else that would be miscible with water and would cause the n-butanol to mix is ethanol or isopropanol. It is also possible that there is some ethylene glycol in there.
Without knowing what the mystery ingredients are, it is going to be hard to separate.

sumatra - 1-10-2018 at 07:48

Quote: Originally posted by macckone  
Something else that would be miscible with water and would cause the n-butanol to mix is ethanol or isopropanol. It is also possible that there is some ethylene glycol in there.
Without knowing what the mystery ingredients are, it is going to be hard to separate.

I will try a variety if solvents and post the results. I am atill thinking of trying the distilles water and salt one more time but in difftent concentrations this time. Will update ASAP.

sumatra - 1-10-2018 at 08:10

Quick update:
A small list of chemicals that MAY be present based on the distillate that comes over at 78 C:
N-butyraldehyde(75 C), ethyl acetate, n-butylamjne, 1-chlorobutane, ethanol, methyl propionate, isopropanol is 82 C and IMO its either this or ethanol.

macckone - 1-10-2018 at 18:48

isopropanol or ethanol would make sense.
both would cause the n-butanol to become miscible.
trying to separate crud isn't always worth it.

sumatra - 7-10-2018 at 11:58

UPDATE:
So I thought that if I distill out the ethanol/isopropanol it would then be easier to separate the liquids with water. Well the lacquer thinner started boiling at the usual 78 C and the temperature increased a bit, but the distillate didn't stop coming over, it slowly reached 90 when I stoppes distilling. Interesting part is that xylene came over too, and its quite a big amount. I added water to the distillate just to test it out, a milky colour appears and then dissapears upon swirling of the flask, something else to note is that after adding water the mixture warms up a bit. Any thoughts?

[Edited on 7-10-2018 by sumatra]