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Author: Subject: Analysis of common OTC and homemade solvents by proton NMR
Texium (zts16)
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[*] posted on 17-11-2018 at 16:53
Analysis of common OTC and homemade solvents by proton NMR


I finally got around to doing something I've been meaning to do for a while- taking samples of several OTC and homemade solvents from my home lab in to my university and seeing how pure they are by proton NMR. These are my results.

All samples were run on a Bruker 400 MHz Avance III NMR spectrometer.

Toluene:
"KleanStrip" brand toluene, over two years old. The sample was taken directly from the original can and diluted with deuterated chloroform. I promise there is a solvent peak on there, it's just really small, because the sample was very concentrated.

Toluene.png - 136kB
The aromatic peaks and the methyl peak of toluene show in the expected locations and ratio. A small water peak can be seen as well. When this is integrated and compared to the toluene peaks, it appears to indicate that the toluene contains approximately 1% water. Otherwise, it looks to be quite clean.

Acetone:
"Crown" brand acetone, purchased a few months ago. The sample was taken directly from the original can and diluted with deuterated chloroform.

Acetone.png - 114kB
This one turned out beautifully: acetone's singlet is the only significant peak. I'm very surprised that there is no water visible.

Diethyl ether:
Fractionally distilled from "Johnsen's" brand starting fluid, which also contains heptanes and some lubricant. A 400 mm Vigreux column was used in the distillation. The ether has been stored in a glass bottle in my freezer since then. The sample was taken from the bottle and diluted with deuterated chloroform.

Et2O.png - 163kB
Diethyl ether's CH2 and CH3 peaks show up right where they're supposed to be, and in a perfect 2:3 ratio for integrals. A peak that could be acetone is visible, but I think this is most likely because I prepared this sample right after the acetone one, and though I used a new pipette, I reused the same bulb, so I think it is merely contamination of the sample. The more troublesome peaks are the spurious ones in the aliphatic region. These are likely due to heptanes that distilled over with the ether. Fortunately, heptanes should not interfere in any reactions that ether would be used as a solvent for. More importantly though, there is no water visible, so drying it for Grignards etc should be relatively easy.

Benzene:
Home made, by decarboxylation of sodium benzoate (food grade from eBay), followed by a second simple distillation. This prep was carried out almost two years ago, and the benzene has been stored in a glass bottle at ambient temperature since then. The sample was taken from the bottle and diluted with deuterated chloroform.

Benzene.png - 117kB

Benzene C13.png - 134kB
For this one I ran a C13 NMR as well, because I saw that on the proton spectrum, although it first appeared to be a single peak as expected, it is actually two very close peaks of different heights. I wasn't sure whether this was just some kind of weird issue with the machine, or if it was an impurity. I'm leaning towards an issue with the machine, because the C13 spectrum looks very clean. A small water peak is visible in the proton spectrum, which integrates to about 1%. Honestly this one looks much better than I had expected it to, considering the nasty orange goop that it was distilled from!

Dichloromethane:
Distilled from "KleanStrip" brand sprayable paint stripper, followed by repeated water washes to remove methanol, drying over calcium chloride, and redistilling. This purification was carried out about a year ago, and the DCM has been stored in a glass bottle in my freezer since then. The sample was taken from the bottle and diluted with deuterated acetone. In retrospect, I'm not sure why I didn't just use chloroform, since their signals really aren't that close.

DCM.png - 125kB
It appears to be pretty pure. I'm not sure what the small spurious peaks on either side of the DCM peak are, or if they are indeed anything at all. There is a very small methanol signature, though it is not visible in the posted picture. It integrates for <0.1%. I'm impressed that the separation from methanol was this efficient.

Chloroform:
Home made using the haloform reaction over a year ago. It has been stored unstabilized at ambient temperature since then in an amber glass bottle. The sample was taken from the bottle and diluted with deuterated methanol.

Chloroform.png - 145kB
This one was rather disappointing. A large acetone peak is visible, which comes out to about 13% by integration when the 6:1 proton ratio is accounted for. Washing the chloroform a few times with water, drying, and redistilling should probably remove the majority of the acetone.


Overall, I'm quite impressed by the relative purity of these solvents. With the exception of the chloroform, these all seem perfectly suitable for most reactions. I attached a good reference for NMR solvent shifts. I've also included a compressed folder containing all of the unprocessed spectra in case anyone else with NMR software would like to take a closer look.

Attachment: NMR Chemical Shifts of Trace Impurities.pdf (661kB)
This file has been downloaded 43 times

Attachment: Solvents NMR Data.zip (3.5MB)
This file has been downloaded 42 times




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UC235
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[*] posted on 17-11-2018 at 17:01


Very interesting. Was the chloroform washed or distilled in any way or just collected from the bottom of the reaction mix? I'd be unsurprised to see so much acetone in a crude product, especially if the bleach wasn't used in particularly large excess. That is somewhat troubling if this is post-drying and distillation though. Acetone forms a high-boiling azeotrope with chloroform that might complicate its removal.

Sulfuric acid is always an option.
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morganbw
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[*] posted on 17-11-2018 at 17:08


Good info.
Thanks
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Texium (zts16)
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[*] posted on 17-11-2018 at 17:18


Quote: Originally posted by UC235  
Very interesting. Was the chloroform washed or distilled in any way or just collected from the bottom of the reaction mix? I'd be unsurprised to see so much acetone in a crude product, especially if the bleach wasn't used in particularly large excess. That is somewhat troubling if this is post-drying and distillation though.
It was post-drying over calcium chloride and distillation. I'm surprised too. I had assumed that most of the unreacted acetone would have gone into the aqueous phase, but I suppose it could have been salty enough to prevent that, and some washes with pure water prior to drying and distillation would be more effective at removing it.

I made the chloroform a long time ago though, and can't recall the exact ratios of hypochlorite and acetone used. It would have been made with 10% NaOCl pool chlorinator as the hypochlorite source, and the same brand of acetone that I analyzed above.




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monolithic
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[*] posted on 17-11-2018 at 18:16


Thank you for taking the time to write this, very useful to know. A few years ago I managed to find a website with a small database of purity (based on NMR samples) for common OTC solvents. I think it was related to a fire department -- I can't remember. Either way, I lost the link. :(

Edit: Found it! Choose from the drop-down menu at the top of the page: http://ilrc.ucf.edu/sample_detail.php?sample_id=2

[Edited on 18-11-2018 by monolithic]
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Mr. Rogers
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[*] posted on 17-11-2018 at 18:31


This is wonderful. The acetone doesn't surprise me and I'd bet most of the store brands would appear similar.
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[*] posted on 17-11-2018 at 19:06


I must say that I'm surprised there is no trace of denatonium benzoate in the acetone.




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Mr. Rogers
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[*] posted on 17-11-2018 at 19:15


Quote: Originally posted by ScienceHideout  
I must say that I'm surprised there is no trace of denatonium benzoate in the acetone.


I've only ever seen this in acetone marketed for nail polish remover - at least they seem to be the only acetone that lists denatonium benzoate on the label.

The HW store acetone usually just lists acetone, in contrast to the other various solvents that are a hydrocarbon witches brew.

[Edited on 18-11-2018 by Mr. Rogers]
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JJay
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[*] posted on 17-11-2018 at 19:22


Would a trace of denatonium benzoate show up? The concentration is surely very low.




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[*] posted on 17-11-2018 at 19:26


Quote: Originally posted by JJay  
Would a trace of denatonium benzoate show up? The concentration is surely very low.


It's usually something like %0.0006 denatonium benzoate in SDA 40B ethanol.
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[*] posted on 18-11-2018 at 02:04


well the benzene looks cool, very pure indeed. orange goop you lost.
i will try making benzene from PET, maybe my professor will let me analize it at university





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12thealchemist
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[*] posted on 18-11-2018 at 02:18


Fascinating and reassuring results! Many thanks for taking the time to carry these out; it's worth knowing roughly how pure one's solvents are. I may be from across the pond, but still very useful information.



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[*] posted on 18-11-2018 at 02:49


Very nice, it confirms acetone is dry of the shelf.
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