At the end of the 1990s, the American chemist, Paul T. Anastas, Professor at Yale and Director of the Green Chemistry Institute, proposed 12 basic principles for developing chemistry techniques more respectful of the environment, christened “Green Chemistry”.

One of the key Green Chemistry indicators, the E factor, defined by Professor R. A. Sheldon, is the ratio between the tonnage of waste and the tonnage of the desired molecule: the lower this ratio, the less polluting the production process.