Sciencemadness Discussion Board

Best/preferred method for cleaning up toluene paint thinner?

SuperOxide - 25-2-2021 at 08:25

I have some toluene that I want to clean up so I can use it as a solvent as well as in some reactions (eg: mono-nitrotoluene synth). I know that the technical grade toluene (such as what's available from Ace Hardware, where I went) has thiophene impurities present, which is what I'm would like to remove as much as possible.

The two methods I've seen are:

  1. Mixing the toluene with a small portion of chilled H2SO4, which will react with the thiophenes bringing them into the lower aqueous layer (obvious by the yellow color change), then separating the toluene off, and repeating this wash a few times. (Seems like most YT videos have gotten this technique from Dougs Lab).
  2. Distilling the toluene over sulfuric acid, which will cause some tar to form in the distilling flask. (I saw this on Extractions&Ire).


My question is - Which of these would be the best? Or should it be both? I have some toluene that I mixed with chilled H2SO4 a few times, then distilled - Should I just add more H2SO4 over it when I distill it? Or is that pointless if I've done the first method listed above? Or is there a better way that I haven't heard of?

Texium - 25-2-2021 at 08:50

Try method 1 first. The toluene that I have purchased from Ace has been thiophene-free. I even verified by proton NMR, along with several other common solvents that I had available: https://www.sciencemadness.org/whisper/viewthread.php?tid=10...

Could be that I just got a good batch, but it's worth checking before you go to the trouble of distillation. You may already be good to go.

SuperOxide - 25-2-2021 at 09:11

Quote: Originally posted by Texium (zts16)  
Try method 1 first. The toluene that I have purchased from Ace has been thiophene-free. I even verified by proton NMR, along with several other common solvents that I had available: https://www.sciencemadness.org/whisper/viewthread.php?tid=10...

Could be that I just got a good batch, but it's worth checking before you go to the trouble of distillation. You may already be good to go.

Oh nice. And I did get mine from Ace as well, and I did the first method of mixing it with chilled H2SO4, stirring it for like 10 minutes, separate, then repeat (maybe 2 more times I believe). By the third wash, the bottom layer wasn't as yellow, but it did look a little different still (and I did a few more H2SO4 washes on a smaller portion, the color seemed to stay the same).

Perhaps I'll do it again with the same toluene and take some photos, let you be the judge.

unionised - 25-2-2021 at 12:30

Do you have any quantitative idea how much thiophene might be present?

I suspect that a lot of commercial toluene is derived from the same product stream that goes into gasoline; made by catalytic isomerisation and aromatization from petroleum alkanes.

If that's the case the sulphur content will be too low to bother about.

Also, if you use your toluene (with some thiophene) to make nitro-toluene then that reaction will include reaction with nitric/sulphuric acids.
And that will destroy any thiophene anyway.

Fery - 25-2-2021 at 12:49

thiophene was a contaminant in toluene of charcoal origin decades ago

SuperOxide - 25-2-2021 at 16:22

Quote: Originally posted by unionised  
Do you have any quantitative idea how much thiophene might be present?
Not really, no. I'd just like to clean it up as best as I can for some future reactions I plan on doing.
Quote: Originally posted by unionised  
Also, if you use your toluene (with some thiophene) to make nitro-toluene then that reaction will include reaction with nitric/sulphuric acids.
And that will destroy any thiophene anyway.

Right, I just figured that maybe it could impact the yield or throw off the freezing points after the reactions done (since I plan on separating the isomers via their freezing points).

Fyndium - 11-4-2021 at 01:51

I found out that one of brands of paint thinner sold in large plastic canisters consists about 30% of water-soluble stuff. Last time I was in need of nonpolar solvent, I got one and just washed it with few doses of water and brine, and it worked fine.

Later when I got time, I distilled it, and found out that about third of the nonpolar boiled before 110C, and I collected and discarded the lower portions, but eventually ended up just collecting most stuff over 100C, because it seemed to work perfectly for any use toluene would. I don't know what it is. It boiled dry hitting ~113C so the rest was basically pure toluene.

So, my routine to get toluene is to wash it with few doses of water, brine and then fractional distill it. If I want really pure, I collect only the spot on 110C.

zed - 11-4-2021 at 08:44

Seems to me, I recall someone reporting that they purchased Thiophene-Free Toluene, from Sherwin-Williams.

A USA Paint company, if they still exist. I'll check. Many US paint manufacturers have expired.

Yup. Still out there. 1gallon, 5gallon, 55Gallon.

[Edited on 11-4-2021 by zed]

Panache - 16-4-2021 at 20:30

If you have the glass vacuum distill from a stirred vessel with a packed short column or a longer unpacked one. I found this better than atmospheric distillation. At the time I used gc to do the assessment.
I thought the thiophene was added. Careful with adding the sulphuric you don’t want ptsA

[Edited on 17-4-2021 by Panache]

SuperOxide - 30-5-2021 at 09:19

Quote: Originally posted by unionised  
Do you have any quantitative idea how much thiophene might be present?

I suspect that a lot of commercial toluene is derived from the same product stream that goes into gasoline; made by catalytic isomerisation and aromatization from petroleum alkanes.

If that's the case the sulphur content will be too low to bother about.

Also, if you use your toluene (with some thiophene) to make nitro-toluene then that reaction will include reaction with nitric/sulphuric acids.
And that will destroy any thiophene anyway.


I went ahead with the toluene nitration (using the toluene I processed) and it worked out pretty well. But even if it would have worked with the thiophene in it, I'm certain it would have impacted the yield since some the thiophene would have reacted with the thiophene instead of the toluene.

Next time I buy some toluene, I will definitely get it from one of the sources mentioned above (as it's suggested they may be thiophene free as it is), but for the toluene I have now - Any suggestions on how I could test for the presence of thiophene? I don't have an NMR, and from what I understand I can't really use the boiling point to check. I get that I probably can't ever get 100% out, but I'd like to get as much out as I can, if possible.

The crude method I used to check if it was present was I just did the sulfuric acid wash until the water layer stopped turning yellow, but if there's a better method, I'd like to try it.

I realize the toluene is probably "good enough" as it is now, but I just prefer to purify the reagents as much as I can, just to remove some variables if a certain reaction goes wrong.

Texium - 30-5-2021 at 12:01

I'm still skeptical that there was even any significant thiophene in your toluene to begin with. If you have Klean-Strip toluene from Ace, that's the same stuff that I got a clean NMR of. Unless they've switched to a crappier source of toluene within the last few years, it's very unlikely it's any different now. You could send me a small sample (no more than 1 mL needed) and I could get an NMR of it, if you're really interested. Looks like the lab I work in has isatin in stock as well, which is a nice qualitative test for the presence of thiophene, as it will react to form a blue dye. I'll test the KleanStrip toluene that I still have at home with that too. I'm always happy when I can use the resources available to me to confirm or debunk common home chemistry rumors.

SuperOxide - 30-5-2021 at 14:09

Quote: Originally posted by Texium  
I'm still skeptical that there was even any significant thiophene in your toluene to begin with. If you have Klean-Strip toluene from Ace, that's the same stuff that I got a clean NMR of. Unless they've switched to a crappier source of toluene within the last few years, it's very unlikely it's any different now.
Well there was certainly some very yellow substance in the water layer when a small amount of chilled sulfuric acid was mixed into it, which lessened as the wash was repeated twice more. What else could that be? If it was toluene (eg: making pTSA or something) then that same thing would have happened in the further washes with the acid, right? Also since it was chilled, I would think very little amount of pTSA would be created.

I didn't get any photos of it, unfortunately. But I do have some unprocessed toluene out back (I only processed about 1L of the gallon I got). If I do, I'll be sure to take some pictures of it when mixing the chilled acid.
Quote: Originally posted by Texium  
You could send me a small sample (no more than 1 mL needed) and I could get an NMR of it, if you're really interested. Looks like the lab I work in has isatin in stock as well, which is a nice qualitative test for the presence of thiophene, as it will react to form a blue dye. I'll test the KleanStrip toluene that I still have at home with that too. I'm always happy when I can use the resources available to me to confirm or debunk common home chemistry rumors.
Thanks for the offer, but Im not sure it's quite that important. But maybe ill take you up on that in the future for some other compounds of interest :-P

Texium - 30-5-2021 at 14:41

Quote: Originally posted by SuperOxide  
Thanks for the offer, but Im not sure it's quite that important. But maybe ill take you up on that in the future for some other compounds of interest :-P
Well, even if you don't feel it's important, I think it actually would be quite important to see if the most common brand of toluene in the US has changed composition in the last few years. I am genuinely interested in checking it out, so I'd be very happy if you could send me a small vial of the unprocessed toluene and one of the cleaned up stuff.

As far as future "compounds of interest" go, that will largely depend on what they are. I won't take anything illegal or legally gray since they'd be run on public university instruments.

LabDIRECT - 3-6-2021 at 05:18

Just FYI - we have about 20-30L of Aviation/Mil-Spec toluene on hand that we need to get rid of so it's going on sale at Labdirectllc.com - feel free to email me at richard.carboni at labdirectllc.com and we can definitely help out a new customer.