Porphyrins are useful molecular compounds in biological systems and for synthetic applications based on their catalytic, optical, and magnetic properties. Synthesis of porphyrins under common methods requires large amounts of environmentally toxic solvents and only a small amount of product is yielded. However, the alternative method via mechanochemistry allows the cyclization step in the porphyrin synthesis process to be solventless (Hamilton,T.D. et al. Faraday Discuss, 2014, 170, 56-69). Equimolar amounts of pyrrole and aldehyde in the presence of an acid catalyst are combined using ball-mill grinding technique. The mixture of reduced-porphyrin precursors is oxidized and purified to obtain yields of tetra-meso-substituted porphyrin similar to or better than those obtained via solvent-based synthesis. Mechanochemically synthesized tetra-substituted porphyrins have been characterized using UV- Vis spectroscopy and 1H-Nuclear Magnetic Resonance. In addition to the previously reported tetra-aryl-substituted porphyrins, a series of tetra-alkyl-substituted porphyrins and very sterically-hindered porphyrins have been synthesized mechanochemically. The addition of Montmorrilonite K10 clay (Plamont et al. Chem. Eur. J. 2013, 19, 11293-11300) as a catalyst for the mechanochemical synthesis was explored, and results will be presented. This study shows the application of mechanochemistry makes it possible to synthesize and isolate a wide range of porphyrins products that are difficult to obtain from solvent-based synthesis.

Expanding the scope of mechanochemical porphyrin synthesis

251st National Meeting (2016)

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