viii: The Chemistry Column
The lazier the greener? Claire Gormley
If you ever carried out a chemistry practical in school, you are likely to remember the big, brown bottles reserved for waste materials, and the strict instructions from your teacher not to pour anything down the sink. An estimated fifty to eighty per cent of the materials left over after a chemical reaction are solvents that can be harmful to the environment, and must be disposed of by special means (Lim, 2015). Solvents are used to dissolve the solid chemicals that are needed to create the desired end product. When chemicals dissolve, the rate at which they mix and collide— making and breaking bonds in the process —increases, thereby speeding up the overall reaction. Apart from this initial dissolving step, these solvents are not usually involved in the reaction process; at the end, they're just there. This is the way that chemistry has been done for decades— but it is changing. Known as 'Lazy Man's chemistry' (a term coined by Tomislav Friščič, a leading scientist in the field at McGill University)— or, more recently, as 'Chemistry 2.0' —mechanochemistry is paving the way for a greener, safer, solvent-free
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approach (Lim, 2015; Friščič, Mottillo, and Titi, 2020). The solvent-free approach comes in many flavours, but, at its core, mechanochemistry is a reaction between two or more chemicals in their solid state over a few days or weeks. Although the process takes much longer than the solvent-based approach— Chemistry 1.0, if you will —in the end, most or all of the reactants are completely used up, and the only thing left is the desired product (Lim, 2015). Currently, the most popular methods for achieving this involve using shaker or planetary mills, which are both available commercially (Friščič, Mottillo, and Titi, 2020). Alternative methods make use of different additives to augment, direct, or enable reactivity between the chemicals. These additives include a small amount of liquid proportional to the reaction weight (Liquidassisted Grinding, LAG), a metal catalyst such as copper, adding certain wavelengths of light (known as Photo-Mechanochemistry, or Mechanochemical Photocatalytic Reactions), and many others (Friščič, Mottillo, and Titi, 2020).
