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Author: Subject: Extraction of diethyl ether — impurities?
thors.lab
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[*] posted on 2-1-2020 at 13:04
Extraction of diethyl ether — impurities?


Hi,

I've just performed the extraction of diethyl ether from Johnsen's premium starter fluid (no. 6732). Here's the SDS.

I started noticing some distillate coming over at 15-20ºC. This was highly suspicious to me as there's nothing as far as I know in there that would come over at that temperature. I brushed it off as being inaccuracy in my crappy little ethanol thermometer at its lower range. It was clearly over 15ºC outside and the thermometer was measuring 15ºC before the distillation. I also could not easily quickly swap out the receiving flask as I had a cooling bath set up below it.

At the end of the distillation I collected 136mL of fluid. At 7.2oz, this would correspond to a 63% concentration of diethyl ether if the yield was 100%! Clearly this was way too high. The datasheet lists the highest concentration of ether at 50%, and I obviously couldn't have gotten 100% yield.

Can anybody take a look at the datasheet and see if I'm missing something? The only thing I can think of that could account for that much mass is the heptane, but we did not reach even near the BP of heptane (maxed out at 34ºC).

Thanks,

Thor




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DraconicAcid
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[*] posted on 2-1-2020 at 13:44


The "sweetened petroleum gases" may contain things like butanes or pentanes, which would distill over at a low temperature.



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thors.lab
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[*] posted on 2-1-2020 at 15:25


Quote: Originally posted by DraconicAcid  
The "sweetened petroleum gases" may contain things like butanes or pentanes, which would distill over at a low temperature.


Alright thanks, I'll redistill and be more selective about which range I'm collecting.




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DraconicAcid
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[*] posted on 2-1-2020 at 15:36


What are you using the ether for? It's possible that they won't interfere with your planned reaction.



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thors.lab
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[*] posted on 4-1-2020 at 21:17


Quote: Originally posted by DraconicAcid  
What are you using the ether for? It's possible that they won't interfere with your planned reaction.


I will be using it to extract p-aminophenol from an aqueous solution.




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[*] posted on 17-1-2020 at 19:24


I've done this distillation and noticed the same thing. I think DraconicAcid is right about lighter hydrocarbons being present. Even with a 10 cm Vigreux column, the difference in boiling points between the hydrocarbons and Et2O wasn't large enough to give good separation. For your planned extraction it shouldn't be a problem. Just be careful to keep the stuff away from sources of ignition, as light hydrocarbons will make the already highly volatile Et2O solution have an even higher vapor pressure.
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[*] posted on 21-1-2020 at 09:50


Quote: Originally posted by thors.lab  
I started noticing some distillate coming over at 15-20ºC.


Acetaldehyde. I too have found that my alleged 35% diethyl ether starting fluid that I bought from the local home improvement store actually contains at least 50% diethyl ether, with the rest being propane and/or butane (at least 30%), while the rest might be acetaldehyde and possibly some other impurities. I was unable to properly identify any hexane or heptane, and while it's possible there might be pentane, I was unable to confirm it.
As to where could the acetaldehyde come from, I think it's a side product from the manufacturing process. From the limited information I was able to find, the industrial route for diethyl ether involves dehydrating ethanol over a hot catalyst, like alumina, and this process has better separation than the sulfuric acid route (Barbet process). Unfortunately, I was unable to find any information about acetaldehyde as side product in this manufacturing process, best I could find is this and a little here. I suspect that the manufacturers might be using a lower quality dehydration catalyst, which might be generating more acetaldehyde as side-product and they don't bother to remove it since it's not worth it, I mean it's very volatile and very flammable, might actually help.
While in my case I didn't see any significant temperature anomalies during distillation, after distillation I decided to test the freshly distilled ether by adding some sodium metal. Immediately, small but constant bubbling began, and after a while a precipitate appeared that eventually turned orange. Removing all the acetaldehyde with KOH and Na metal took many weeks, and even so there are still traces left.

You should test your distillate and see if there are any ketones present.

[Edited on 21-1-2020 by Mabus]




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[*] posted on 22-1-2020 at 13:07


Wouldn't it be possible to remove acetaldehyde via its bisulfite adduct?

For better fractionation, I usually use water or oil bath of known temperature and a Hempel column filled with glass or ceramic Rashig rings. It works much better for e.g. ethanol where even tall Vigreux column fall short.
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