[uglepik]

Hi guys,

I'm running TLCs of some primary amines and I'm not sure what to add to the eluant to make them run better. I've been playing around with bases such as DIPEA/DIEA and TEA but as both up them show up prominently when I stain with KMnO4 I would like something else. What do you guys add when running amines?

(my eluants are chloroform-based and have polarities around that of neat chloroform with 5-15% methanol)

[fledarmus]

I usually use TEA. It is volatile, so if your primary amine isn't, you might try drying your plate over a heat gun before you stain it.

[uglepik]

I have tried drying the plate, but even with pretty long drying it still turns yellow when stained with KMnO4.

[nox]

Why not try a ninhydrin stain? I don't think I've observed tertiary amines light up on the TLC when stained, certainly not TEA.

[Dan]

I have tried drying the plate, but even with pretty long drying it still turns yellow when stained with KMnO4.

Dry it for longer. I regularly stain TEA-doped silica plates with KMnO₄, but you need to get it really hot with decent heat gun, then let it cool off for a minute before staining.

If your heat gun doesn't have the power required, then heat it up as much as possible and put it under vacuum for a while.

[uglepik]

Nox> I have played around with ninhydrin stains, but the results haven't really been to my liking. Haven't tried much I must say.

Dan> My heat gun is absolutely bad ass ;-) You are probably right that I should heat it for longer. I have tried heating for several minutes at around 100 oC, but apparently I need more. What temperature and heating time do you use (more or less)?

[Dan]

What temperature and heating time do you use (more or less)?

It's a Bosch PHG 600-3, and I heat at full power for probably around 30 seconds. According to the specs that's 600^oC, so much hotter than you're using.

A tip - make your plate a bit wider than required, and after heating put a drop of permanganate dip on a clear area to see if it's TEA-free. Heat more if necessary.

[uglepik]

What temperature and heating time do you use (more or less)?

It's a Bosch PHG 600-3, and I heat at full power for probably around 30 seconds. According to the specs that's 600^oC, so much hotter than you're using.

A tip - make your plate a bit wider than required, and after heating put a drop of permanganate dip on a clear area to see if it's TEA-free. Heat more if necessary.

Okay, that's pretty rough!!! Don't you char your products (and the silica plate) at this temperature? Anyway, I'll try it out. The wide plate tip seems to be a good idea. Thanks!

[Dan]

Don't you char your products (and the silica plate) at this temperature?

The products do sometimes char a bit, I normally stop heating when that happens. I doesn't really matter - you are about to chew it up with permangante anyway.

I've never managed to char the silica.