Metrics of Green Chemistry and Sustainability: Past, Present, and Future

Abstract

The first green chemistry metricsthe E factor (kgs waste/kg product) and atom economy (mol wt of product/sum of mol wts of starting materials)were introduced in the early 1990s and were actually green chemistry avant la lettre. In the last two decades, these two metrics have been adopted worldwide by both academia and industry. The E factor has been refined to distinguish between simple and complete E factors, for example, and to define the system boundaries. Other mass-based metrics such as process mass intensity (PMI) and reaction mass efficiency (RME) have been proposed. However, mass-based metrics need to be augmented by metrics which measure the environmental impact of waste, such as life cycle assessment (LCA), and metrics for assessing the economic viability of products and processes. The application of such metrics in measuring the sustainability of processes for the manufacture of pharmaceuticals and other fine chemicals is discussed in detail. Mass-based metrics alone are not sufficient to measure the greenness and sustainability of processes for the conversion of renewable biomass vs fossil-based feedstocks. Various metrics for use in assessing sustainability of the manufacture of basic chemicals from renewable biomass are discussed. The development of a sustainable biobased production of chemicals meshes well with the concept of a circular economy, based on resource efficiency and waste minimization by design, to replace traditional linear, take−make−use−dispose economies.

The Hydrophobic Effect Applied to Organic Synthesis: Recent Synthetic Chemistry “in Water”

“…[2] Likewise, the waste water streamsc ontaminated by miscible solvents further exacerbatet his major environmental problem. [3] Unfortunately,m odern organic synthesis sees water mainly as the workup medium, rather than the reaction medium. But imagine if reactions could be run under mild conditions with the same or better levels of efficiency and selectivity in water;t hen the need for organic solvents as the medium and the associated even larger volumes of water used for reaction processing are both obviated.…”

A Common, Facile and Eco‐Friendly Method for the Reduction of Nitroarenes, Selective Reduction of Poly‐Nitroarenes and Deoxygenation of N‐Oxide Containing Heteroarenes Using Elemental Sulfur

“…Next, we evaluated the green chemistry credentials for our protocol using E‐ factor (see details in Supporting information for calculations) . In general, the protocol presented good E ‐factor values from 3.26–7.85 for reduction of nitroarenes, from 1.98–3.01 for the deoxygenation of benzofuroxans and from 1.60–2.38 for the phenazine N , N ' ‐dioxides.…”

Chemoenzymatic Halocyclization of γ,δ‐Unsaturated Carboxylic Acids and Alcohols

“…In the current contribution, we have expanded the scope of Ci VCPO as a biocatalyst for organic synthesis. A semiquantitative comparison of the proposed chemoenzymatic halolactonization and haloetherification reaction with established protocols demonstrates its potential environmental benefits (Table ). The mass intensities of the chemical and chemoenzymatic reactions are comparable.…”