Solvents are critical components in chemical production. They can be used to promote chemistry, dissolve reactants, modify solute properties, remove impurities/byproducts, isolate products, etc.

How Solvents Relate to Green Chemistry

The extensive use of solvents, however, may increase environmental burden and health risks because many organic solvents are flammable, volatile, and even toxic. An analysis report by the American Chemical Society Green Chemistry Institute Pharmaceutical Roundtable (the Roundtable) suggests that typically >70% of pharmaceutical wastes are solvent-related (i.e., solvent and water consumption). Therefore, solvent choice is a key factor when trying to conduct green chemistry.

The selection of solvents should follow the principles of green chemistry to minimize waste and improve safety. The directly related principles are

  • Safer Solvents and Auxiliaries
  • Inherently Safer Chemistry for Accident Prevention
  • Eliminate and Minimize Hazards and Pollution


Selection Guide

Prat et al. published CHEM21 selection guide based on health, safety, and environmental criteria, which includes not only classical solvents, but also emerging solvents, such as bio-derived solvents.

Solvents are defined as

  • Recommended: solvents to be tested first in a screening exercise, if of course there is no chemical incompatibility in the process conditions.
  • Problematic: these solvents can be used in the lab, but their implementation in the pilot plant or at the production scale will require specific measures, or significant energy consumption
  • Hazardous: the constraints on scale-up are very strong. The substitution of these solvents during process development is a priority
  • Highly Hazardous: solvents to be avoided, even in the laboratory 


Full lists of solvent selection guide are shown below.

CHEM 21 solvent guide of classical solvents

Family Solvent Ranking
Water Water Recommended
Alcohols MeOH Recommended
EtOH Recommended
i-PrOH Recommended
n-BuOH Recommended
t-BuOHc Recommended
Benzyl alcohol Problematic
Ethylene glycol Recommended
Ketones Acetone Recommended
MEK Recommended
MIBK Recommended
Cyclohexanone Problematic
Esters Methyl acetate Problematic
Ethyl acetate Recommended
i-PrOAc Recommended
n-BuOAc Recommended
Ethers Diethyl ether Highly Hazardous
Diisopropyl ether Hazardous
MTBE Hazardous
THF Problematic
Me-THF Problematic
1,4-Dioxane Hazardous
Anisole Recommended
DME Hazardous
Hydrocarbons Pentane Hazardous
Hexane Hazardous
Heptane Problematic
Cyclohexane Problematic
Me-cyclohexane Problematic
Benzene Highly Hazardous
Toluene Problematic
Xylenes Problematic
Halogenated DCM Hazardous
Chloroform Highly Hazardous
CCl4 Highly Hazardous
DCE Highly Hazardous
Chlorobenzene Problematic
Aprotic polar Acetonitrile Problematic
DMF Hazardous
DMAc Hazardous
NMP Hazardous
DMPU Problematic
DMSOc Problematic
Sulfolanec Hazardous
HMPA Highly Hazardous
Nitromethane Highly Hazardous
Miscellaneous Methoxy-ethanol Hazardous
Carbon disulfide Highly Hazardous
Acids Formic acid Problematic
Acetic acid Problematic
Ac2O Problematic
Amines Pyridine Hazardous
TEA Hazardous


CHEM 21 solvent guide of emerging solvents 

Family Solvent Ranking
Alcohols i-Butanol Recommended
i-Amyl alcohol Recommended
1,3-Propane diol Problematic
Glycerol Problematic
Esters i-Butyl acetate Recommended
i-Amyl acetate Recommended
Glycol diacetate Recommended
γ-Valerolactone Problematic
Diethyl succinate Problematic
Ethers TAME Recommended
CPME Problematic
ETBE Problematic
Hydro-carbons D-Limonene Problematic
Turpentine Problematic
p-Cymene Problematic
Aprotic polar Dimethyl carbonatec Recommended
Ethylene carbonated Problematic
Propylene carbonate Problematic
Cyrene Problematic
Miscella-neous Ethyl lactate Problematic
Lactic acid Problematic
TH-furfuryl alcohol Hazardous


Selection Tool

The guide above provides a quick selection of green solvents. We have to recognize, however, that some solvents offer unique properties that are vital for some classes of reaction and therefore, the need from a solvent may vary. 

This interactive tool - Solvent Selection Tool, created by the Roundtable, allows you to select greener and safer solvents from 272 solvents in the database based on the Principal Component Analysis (PCA) of the solvent's 70 physical properties.

After filtering by Functional Groups, Physical Properties, Engineering, International Conference on Harmonization (ICH), Safety, Health and Environment (SHE) based on the process needs, solvent shortlist will be available.

Looking forward, more comprehensive selection guide may be developed and employed as the promotion of green solvents is a trend due to the development of green chemistry, and the increasing regulation as well.



  1. American Chemical Society
  2. Prat, D., Wells, A., Hayler, J., Sneddon, H., McElroy, C.R., Abou-Shehada, S. and Dunn, P.J., 2015. CHEM21 selection guide of classical-and less classical-solvents. Green Chemistry, 18(1), pp.288-296.
  3. Diorazio, L.J., Hose, D.R. and Adlington, N.K., 2016. Toward a more holistic framework for solvent selection. Organic Process Research & Development, 20(4), pp.760-773.

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By Olica Xu


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