Mechanochemistry – A Powerful and “Green” Tool for Synthesis BY ANDREW SASSER '23 Cover Image: This scientist is using a mortar and pestle to grind different reagents and facilitate a mechanochemical reaction. Unlike most synthetic reactions, mechanochemical reactions do not require any solvent Source: Flickr.com
Introduction Over the past two centuries, the field of synthetic chemistry has experienced remarkable growth. Prior to the 19th century, scientists accepted the doctrine of vitalism, which suggested that living organisms were fueled by a “vital force” separate from the physical and natural world, and that organic compounds could not be synthesized from inorganic reagents. However, following Friedrich Wohler’s 1828 synthesis of the organic molecule urea from the inorganic molecule ammonia, the field of synthetic chemistry exploded, with chemists producing compounds such as the anti-cancer drug Taxol and the pesticide Strychnine from simple organic and inorganic reagents (Museum of Organic Chemistry, 2011). Modern synthetic techniques, however, still have some significant drawbacks. For one, synthetic schemes can be highly inefficient. On average, the synthesis of fine chemicals produces 5-50
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kilograms(kg) of by-product per kg of product, and the synthesis of pharmaceuticals can generate over 100 kg of waste product per kg. Second, most syntheses use toxic solvents, which often comprise the largest amount of “auxiliary waste.” (Li and Trost, 2008). Third, reactions can also require a large amount of energy, especially if heating is necessary. As a result of these inefficiencies, the field of “Green Chemistry” has been developed to maximize atom economy – the ratio of the mass of the atoms in the product to that of the reagents – and thus promote efficiency (Chen et. al, 2015). In an effort to minimize waste products, some chemists have turned towards solventless reactions to promote higher product recovery. One class of solventless reactions, referred to as mechanochemistry, uses mechanical force to promote chemical reactions. This paper will demonstrate how mechanochemical reactions have not only reduced energy requirements and improved atom economy but have also DARTMOUTH UNDERGRADUATE JOURNAL OF SCIENCE
