[shrikantvarma]

when to use hexane/ ethyl acetate & MDC/methanol mixture for column chromatography,i seen maximum elution in column chromatography with hexane/ethyl acetate why MDC/methanol is not use generally for elution purpose??

[jchan123]

Both solvent systems are commonly used for chromatography purposes.  Typically, the DCM/MeOH combination is used to purify more polar compounds.  Keep in mind, you will start to dissolve silica when your MeOH content is increased to a certain level.

[ardbeg]

methanol dilution of silica seems like a myth to me.  i have run columns on horrible stuff in 50:50 MeOH/EtOAc and only tiny tiny amounts of silica made it through the column into my product.  and if you do get any in there, just dissolve the compound in minimal DCM, filter it off, and youre fine.  never found it to be a problem.

[jchan123]

Hey ardbeg,

You are correct in the sense that only smalls amounts (even using 1:1 DCM/MeOH mixture) are ever dissolved.  When it does happen, its sometimes difficult to detect.  For instance 1H and 13C NMR will not be able to detect the silica present. 

[pacifyer]

I hate methanol, because it is poison, and you cannot smell it. It is especially bad for your eyes...

[Med90]

usually, dichloromethane and methanol combination is used for more polar compounds. Using ethylacetate and hexane, you may have problem with precipitation which results in poor separation.

[shrikantvarma]

when i prepared column in MDC i observe column breaks it not remain uniform, how to overcome this problem??

[Med90]

putting enough solvent and applying gentle pressure from top should work to prevent breaks..