Reaction Scale and Green Chemistry: Microscale or Macroscale, Which Is Greener?

摘要

The different ways microscale and green chemistry allow reducing the deleterious impacts of chemistry on human health and the environment are discussed in terms of their different basic paradigms: green chemistry follows the ecologic paradigm and microscale the risk paradigm. A study of the synthesis of 1-bromobutane at macro- microscale (109.3 10.9 g of the limiting reagent, butan-1-ol) showed that green chemistry mass metrics (AE, atom economy; RME, reaction mass efficiency; MI, mass intensity; E -factor, environmental factor; CEE, carbon efficiency) are unsuitable for evaluating the advantages of micro- versus macroscale. Poorer values of mass metrics at the microscale and the same green star at both scales showed that green metrics do not recognize that microscale improves safety. As so far no metrics have been proposed for evaluating this purpose, a new risk index (scale risk index, SRI) was developed for assessing the improvement of safety on downsizing the scale of synthesis experiments in chemistry teaching laboratories. The performance of SRI to show the benefits of microscale was assessed for syntheses of 1-bromobutane, tetramminecopper(II) sulfate monohydrate, and dibenzalacetone.