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Author: Subject: Distilling PVC cement
ninhydric1
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[*] posted on 21-11-2018 at 13:08
Distilling PVC cement


PVC cement has two major solvents that I'm after; tetrahydrofuran and cyclohexanone, with acetone and MEK also present. Separating the cyclohexanone and MEK is pretty simple through simple distillation. However, THF and acetone form an azeotrope (~86% acetone, ~14% THF IIRC) that boils slightly below the BP of acetone. Both are, unfortunately, miscible with water. Since I'm after the THF, is there any way to separate the two? Destroying the acetone (without destroying the THF) through some chemical method is viable, if there is one, as acetone is dirt cheap for me.



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JJay
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[*] posted on 21-11-2018 at 13:35


Stirring with a large excess of aqueous saturated sodium bisulfite solution followed by distillation will remove the acetone. You can get rid of sulfur dioxide in the distillate by stirring it with potassium carbonate.

I have not tried this with THF specifically, but I am sure it will work




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ninhydric1
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[*] posted on 21-11-2018 at 19:46


However, Wikipedia states that bisulfite will form adducts with some cyclic ethers (on the page for sodium bisulfite, under the "Reactions" tab), and I'm not sure if THF will also complex with bisulfite.



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[*] posted on 21-11-2018 at 21:08


The authors of this paper seemed to think that forming a bisulfite adduct was a good way to extract their target compound from THF: https://pubs.acs.org/doi/abs/10.1021/op0202235

What would be the structure of a THF-bisulfite adduct?




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ninhydric1
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[*] posted on 21-11-2018 at 21:14


Oh nevermind, I misread the article, my bad. Cyclic ketones not cyclic ethers. I'll do a bisulfite washing tomorrow and another distillation and report back the results.

Are the acetone-bisulfite (and maybe a bit of MEK- bisulfite) adducts soluble in THF or sat. bisulfite? A filtration (if they are insoluble) might make it easier to work with.




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draculic acid69
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[*] posted on 22-11-2018 at 22:40


I tried this on ce and got pure thf using a 4ft 10 mm wide copper tube coming out of a as kettle on a hotplate.going by temp and weight (which were spot on)we were pretty sure the thf was pure.smell also seemed to be ketone free.
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[*] posted on 22-11-2018 at 22:46


Quote: Originally posted by ninhydric1  
Oh nevermind, I misread the article, my bad. Cyclic ketones not cyclic ethers. I'll do a bisulfite washing tomorrow and another distillation and report back the results.

Are the acetone-bisulfite (and maybe a bit of MEK- bisulfite) adducts soluble in THF or sat. bisulfite? A filtration (if they are insoluble) might make it easier to work with.


Acetone-bisulfite adducts seem to be quite soluble in saturated sodium bisulfite solution with no metal ions present except for sodium. I have noticed a precipitate forming in them when they stand for a long time, but I have never investigated to see exactly what it is.




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