The “E-factor” is a metric of how environmentally friendly, or harmful, a chemical process is. Specifically, the “E-factor” is the ratio of kilograms of waste generated per kilogram of product synthesized. Thus the lower the E-factor, the more environmentally benign a process should be. Of course, this is only a single metric, and other factors, like the toxicity of the waste produced, should also be taken into account. In pharmaceutical companies, the E-factor for the synthesis of drug products is typically in the range of about 25 to 100.