Sciencemadness Discussion Board

Why is [stabilized] toluidine usually sold with glacial acetic acid?

SuperOxide - 30-5-2022 at 13:12

Im making some ortho-toluidine, which I have done once before over a year ago, and one thing I remembered is how quickly it degraded. I vacuum distilled it, stored it in an amber bottle that was purged with nitrogen. But despite these steps the toluidine still degraded much quicker than I had expected.
In one of Benigniums replies he mentioned that the toluidine could be stored as the salt which he theorized may be more stable. However I just caught up with him about it and it turns out that even that degrades (he said its now a grey powder).

I looked into how o-toluidine is sold from main suppliers (Sigma Aldrich, for example) and they sell it as a 0.6 M in glacial acetic acid, contains thiourea as stabilizer (PubChem page, which makes sense. I have the thiourea, but I was wondering what the purpose of the GAA was? I couldn't find a decent description for its purpose. There are a lot of Google results about determining the amount of blood glucose using the mixture, but not much about why the GAA is used.

If anyone has any insight then it would be greatly appreciated. Regardless, I do plan on running a little test. I'll vacuum distill some of the toluidine, then have a control, a mixture with oT+thiourea, and oT+GAA+thiourea, and see how quickly they degrade compared to the control (probably just by looking at the color, lol)

P.S. Sorry for the 2nd post about toluidine in 2 days, hope I don't catch any flack for that >_<

clearly_not_atara - 30-5-2022 at 15:22

The key difference between a salt powder and a solution in GAA is that it excludes oxygen somewhat decently.

SuperOxide - 30-5-2022 at 15:40

Quote: Originally posted by clearly_not_atara  
The key difference between a salt powder and a solution in GAA is that it excludes oxygen somewhat decently.

No, sorry, I think I may have stated that incorrectly. The GAA/thiourea is for the freebase o-toluidine. Not for the o-toluidine HCl.

o-Toluidine solution, 0.6 M in glacial acetic acid, contains thiourea as stabilizer

I was just saying that I was trying to say that the HCl didn't seem to be as stable as I wanted.

However, I may have found the answer. I think the GAA solution isn't meant for synthesis, but for specific use in the colorimetric determination of glucose (I think...).
So if that's the case, then I don't need the GAA, just the thiourea. I'm not sure how much thiourea is needed to stabilize a given amount of oT.

[Edited on 30-5-2022 by SuperOxide]

[Edited on 31-5-2022 by SuperOxide]

numos - 30-5-2022 at 21:24

I think you mostly figured it out but maybe this will help anyway.

It's not usually sold in acetic acid, this solution specifically is "for use in the colorimetric determination of glucose." This is a specialty solution sold at a high price for a specific purpose and does not seem useful for synthesis. This compound for use as a reagent in synthesis is dirt cheap and sold neat: https://www.sigmaaldrich.com/US/en/product/aldrich/466190

o-toluidine, just like aniline and most other amines, oxidizes in air and degrades/darkens over time. These compounds are generally distillated right before use to ensure a clean product. The HCl salts of most amines are more stable, partly because they are generally solids that can be crystallized, and crystals degrade slower. I would not bother with the thiourea, this seems like some sort of radical/peroxide trap... maybe to prevent amine oxidation, but I think you will still get degradation and now you have a smelly mess. Just distill it right before you use it, the "degradation" is often superficial and may only affect the purity by a couple %.


[Edited on 5-31-2022 by numos]

SuperOxide - 31-5-2022 at 08:39

Quote: Originally posted by numos  
It's not usually sold in acetic acid, this solution specifically is "for use in the colorimetric determination of glucose." This is a specialty solution sold at a high price for a specific purpose and does not seem useful for synthesis. This compound for use as a reagent in synthesis is dirt cheap and sold neat: https://www.sigmaaldrich.com/US/en/product/aldrich/466190
I did see this as well, but when I looked into "o-toluidine stabilized" and found the thiourea (which I just got today) I guess I got my hopes up that it was an adequate stabilizer.

Quote: Originally posted by numos  
o-toluidine, just like aniline and most other amines, oxidizes in air and degrades/darkens over time. These compounds are generally distillated right before use to ensure a clean product. The HCl salts of most amines are more stable, partly because they are generally solids that can be crystallized, and crystals degrade slower. I would not bother with the thiourea, this seems like some sort of radical/peroxide trap... maybe to prevent amine oxidation, but I think you will still get degradation and now you have a smelly mess. Just distill it right before you use it, the "degradation" is often superficial and may only affect the purity by a couple %.

Yeah, when I used it before it had degraded more and more each time, but I never really noticed any issues with it. I guess its just irritating when everything else is decently pure then you have this nasty poopy smelling liquid that's now even dark brown or black.
I know I can distill it, but that's a vacuum distillation that I was hoping to avoid having to do.