Greener Flash Whitepaper

As environmentally responsible chemists we all want to reduce the chemical waste volume we generate in our daily research activities. While the chemicals we use are necessary for what we do, there are ways to minimize not only the volume of organic solvents used but also to replace hazardous chemicals with safer solvents.

The part of the synthesis workflow that is most solvent intensive, of course, is flash chromatography. This technique typically consumes hundreds of milliliters or more per chromatographic run, even for low milligram level purification.

Flash chromatography methods are often developed using thinlayer chromatography (TLC) which may not always supply the desired results. This is because of silica property differences, both physical and chemical, between the TLC plate and column or even the differences in mass transfer kinetics between the
techniques. These differences can result in purifications that either do not provide enough separation, requiring re-purification, or too much separation, with both situations wasting solvent.

Typical solvents used with straight-phase (normal-phase) flash chromatography include hexane or heptane, ethyl acetate, dichloromethane, and methanol. These solvents can be hazardous, especially dichloromethane, which is now proposed to be banned in the US by the EPA1 , but they are also expensive to buy and dispose. In fact, solvent disposal costs can be 5 to 10x higher than their purchase price2. Organic waste also adds CO2 and other pollutants to the atmosphere when they are incinerated3  which is the most common disposal method by chemical waste companies.

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