Sciencemadness Discussion Board - Acidic Al2O3 for chromatography,a request for advice.

Acidic Al2O3 for chromatography,a request for advice.

Admagistr - 26-11-2021 at 17:11

I bought 1 kg of this oxide cheaply, it's labelled as acidic and the label doesn't indicate its exact chemical composition or its purity. Does anyone know it? I want to use them for inorganic synthesis, and I don't know if he's right for that? Thanks!

Dr.Bob - 28-11-2021 at 17:52

There are specs available for how neutral alumina is treated to make it either basic or acidic. Just google "how to make acidic alumina" or something like that to find it. Mostly it is washing it with acid or base solutions, which alter the effective "pH" of the solid.

But these treatments are designed for chromatography. Basic alumina has weaker atraction to amines, typically, so it is good for separating amines, as they don't stick to it like glue. Same way, acid alumina is good for chromatographing organic carboxylic acids and other acids with simple ethyl acetate and hexanes. But for chemstry, you may be able to use it as is, or maybe to adjust the pH for some reactions, but simpler to just find neutral alumina Al2O3 if you are really unsure.

Admagistr - 28-11-2021 at 18:14

Quote: Originally posted by Dr.Bob

There are specs available for how neutral alumina is treated to make it either basic or acidic. Just google "how to make acidic alumina" or something like that to find it. Mostly it is washing it with acid or base solutions, which alter the effective "pH" of the solid.

But these treatments are designed for chromatography. Basic alumina has weaker atraction to amines, typically, so it is good for separating amines, as they don't stick to it like glue. Same way, acid alumina is good for chromatographing organic carboxylic acids and other acids with simple ethyl acetate and hexanes. But for chemstry, you may be able to use it as is, or maybe to adjust the pH for some reactions, but simpler to just find neutral alumina Al2O3 if you are really unsure.

Thank you very much Dr.Bob, this information is good enough for me. It's best to ask someone who's had practice with it, like you. Encyclopedia/Google is a second possibility, but sometimes incorrect information appears there...The last time I discovered quite a bit of nonsense on the English version of Wikipedia, when I was read "expert" posts about gems...