Atom economy, expanding boundaries to incorporate upstream reactions

In this work, we address one of the overall shortcomings of atom economy and the limited scope of the boundaries chosen. While atom economy is not the only measure of a process' sustainability, it is a valid comparison from a materials usage view. With this in mind, many publications in green chemistry focus on atom economy as a method for estimating the environmental impacts of a reaction scheme to reach a desired product. The choice of which reactions are considered in the atom economy analysis, or the system boundaries, plays as great of an importance as it does in performing life cycle assessments. Most applications of atom economy begin their analysis with manufactured intermediates and follow a short chain of reactions to the final products. This ignores any upstream processing that was done to create the intermediates and may skew results to incorrectly favor one of the proposed reaction schemes. Here, we develop a simple expression for atom economy that aggregates overall reaction stoichiometries for a chain of reactions leading from raw materials to the final products. We find that by expanding the boundaries to incorporate upstream manufacturing of raw materials, the overall atom economy changes substantially. In order to fully utilize atom economy, system boundaries must encompass upstream reactions in order to prevent sub-optimal materials usage. In this paper, we calculate the overall atom economy of two reaction schemes for synthesizing 1,3-propanediol. This system was chosen as a case study to highlight the choice of system boundaries. By implementing the aforementioned equation to include the upstream processing reactions it is found that the atom economy of each process is no longer 100% as had been reported previously.