Greenness of chemical reactions – limitations of mass metrics

Abstract

The influence of reaction conditions (yield, excess of stoichiometric reagent, molecular weights of reagents, and mass of auxiliary materials and solvents) on the values of several green chemistry mass metrics (E-factor, mass intensity, atom utilization, relative mass efficiency, and element efficiency), for reactions with 1:1 and 1:3 stoichiometries, has been analyzed, as well as relationships between the metrics. The theoretical behavior of these, when visualized by three-dimensional graphic representations, e.g. surfaces of metric = f(yield, excess), together with the experimental values, facilitates the management of its improvement – changes in conditions in successive experiments should follow the directions shown by the graph. The study shows that there are practical limitations to the greenness increase due to the complex nature of the chemistry but confirms that it is worthwhile to pay more attention to the effort of obtaining quantitative details of the laboratory syntheses to acquire information to assess greenness.

Keywords:

• Green metrics
• green synthesis
• reaction greenness improvement
• green chemistry education

Acknowledgements

The authors wish to thank the pre-service teachers Olga M.S. Martins and M. Salomé Fernandes for their support in the laboratory work. M.G.T.C.R. work has been supported by Fundação para a Ciência e a Tecnologia through grant no. PEst-C/EQB/LA0006/2011.