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Extrusion: an efficient technique for the manufacture of organic compounds and materials
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Introduction: Herein, we describe a sustainable route to the solvent-free continuous large-scale manufacture of high quality chemical products by employing twin screw extrusion (TSE).
Methods: Mechanochemistry is a rapidly developing synthetic method typically involving the grinding of solid reagents together under solvent-free or low-solvent conditions. Recently, mechanochemical synthesis has been scaled up from gram to multi-kghr-1 quantities by employing an established process - TSE (Figure 1).
Figure 1: Laboratory sized Twin Screw Extruder and a colour change observed upon carrying the Knoevenagel condensation.
Results and Discussion: We have demonstrated that TSE is very efficient for synthesising Metal Organic Frameworks (MOFs), including HKUST-1, ZIF-8 and Al(fumarate)(OH) as well as Deep Eutectic Solvents (DESs). These materials, which are of similar or enhanced quality to those commercially available commercially, were prepared on a 1 kghr-1 scale. Extrusion allows the preparation of these materials within 2 minutes, and in the case of DESs, thermal degradation, which is known to occur in the conventional preparation of these materials, was avoided. This is a step change in the preparation of DESs and in turn ionic liquids which are a similar family of materials.
A variety of condensation reactions have been investigated and the effect of the wettability of a solid reagent was investigated and found to have a significant effect on the reactive process taking place. Within this work, examples of chemoselectivity were observed in the absence of a catalyst which is typically required in solution. Furthermore, multicomponent reactions and telescoping reactions (subsequential reactions taking place in one process) have been optimised.
The synthesis and subsequent amorphisation of APIs, such as paracetamol, has also been demonstrated employing TSE. This was carried out at relatively low temperatures, in the presence of citric acid (an innocuous excipient used in the pharmaceutical industry). |
