[splitsec86]

I am curious to know the answer to this, although it has no bearing to my research work.

So I notice that before I conduct flash chromatography, I start with white silica. After I finish, and I flush the column out with polar solvents, often I see the silica has turned a different colour (i.e. brown, yellow, orange). Its understandable that if there was still organic material there, that would be the reason for the residual colour, but i would assume that, after flushing the column out thoroughly, most if not all, material would have come out which should leave the same white coloured silica I started with. I'm curious to know what could have caused the colour change on the silica.

[Furanone]

Is there possibly a pH change during this flushing process?

[hypervalent_iodine]

I am curious to know the answer to this, although it has no bearing to my research work.

So I notice that before I conduct flash chromatography, I start with white silica. After I finish, and I flush the column out with polar solvents, often I see the silica has turned a different colour (i.e. brown, yellow, orange). Its understandable that if there was still organic material there, that would be the reason for the residual colour, but i would assume that, after flushing the column out thoroughly, most if not all, material would have come out which should leave the same white coloured silica I started with. I'm curious to know what could have caused the colour change on the silica.

Why would you assume that? What are you flushing with?

[splitsec86]

I flush out the column with ethyl acetate or with 90:10 dichloromethane/methanol

[hypervalent_iodine]

I flush out the column with ethyl acetate or with 90:10 dichloromethane/methanol

In that case, it is quite likely that not everything has come off. If you flush with higher concentrations or straight methanol, it should remove anything left. Though, if you're having to do that to remove the compound you're after, I would suggest looking into other purification methods.

[atije]

So I notice that before I conduct flash chromatography, I start with white silica. After I finish, and I flush the column out with polar solvents, often I see the silica has turned a different colour (i.e. brown, yellow, orange). Its understandable that if there was still organic material there, that would be the reason for the residual colour, but i would assume that, after flushing the column out thoroughly, most if not all, material would have come out which should leave the same white coloured silica I started with. I'm curious to know what could have caused the colour change on the silica.

I don't consider ethyl acetate or DCM:MeOH (90:10) polar :-) In most of the reactions I run, some discoloration appears (brown/yellow), and this almost always sticks to the top of the silica, even in relatively polar eluents. I most of the time have no idea what these compounds are and they don't disturb anything. I would also flush with methanol or ethanol:water mixtures if you really, really want it to come off...