Chromatography
[Chromatography Decision Tree](https://“Green Chromatography” Decision Tree)
For flash chromatrography and HPLC, try a 3:1 (v/v) solution of ethyl acetate/ethanol as an alternative to dichloromethane (DCM). DCM is a greenhouse gas with a high carbon footprint. Chlorinated solvents also have negative acute and chronic health effects on humans.
Taygerly et al. green solvent alternatives guide. To see more clearly, please right click → open in new tab
Reverse Phase Chromatography
Try C18 ISCO columns
- They use less glass and because they have a shorter run time than multiple injection prep HPLCs, there is less solvent waste
- No need to use DCM to purify polar compounds
- columns are reusable
Silica Gel Chromatography
Don’t assume the solubility of mixed solvents is linear. Molecules can be much more in a mixture than in either of the individual solvents. So it may be advantageous to use solvent mixtures to run at higher concentrations rather than diluting out. This allows for better work-up efficiency and allow for purification by evaporation crystallization.
Silica columns can be reused. The ACS Green Chemistry Roundtable suggest the following protocol:
*Using TLC as a guide, flush column with polar eluent to flush remaining material from column. Pre-columns/loading columns can be used as a way to minimize baseline material remaining on the column.
*Re-equilibrate with desired gradient mixture or flush with air to remove solvent for later use.
*Air pockets may form that will alter performance due to inconsistent packing of the stationary phase.
As discusssed above, use 3:1 (v/v) solution of ethyl acetate/ethanol as an alternative to dichloromethane (DCM). See general chromatography section above for more details.
Extractions
Consider potassium carbonate instead of sodium chloride as a salting out additive (providing your molecule is not base-sensitive). Potassium carbonate has a higher ionic strength, so less will be needed to salt out your product.
Switch out HCl (aq) with acetic acid (aq) for low molecular weight amines.
Dipolar Aprotic Solvent Extraction
- Extract with less polar solvents first to minimize DMF/DMSO on your product
Recrystallization
The solubility of wet and dry solvents is different and this can be used to your advantage.
For example, you may be able to do your extraction work-up in water wet solvents and then azeotropically dry your sample to crystallize our your product.
- Works well for methly ethyl ketone
Ion Exchange
Other
For Green Analytical Chemistry, including analytical chromatography, please see this section here.
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