Porphyrins are useful molecules, not only as model compounds for biological systems, but also for their demonstrated catalytic, optical, and magnetic propertities. Currently, the protocols for synthesizing and purifying porphyrins require a large amount of solvents which are toxic to the environment, and still yield only a small amount of product. However, it is possible to eliminate the solvent used for the cyclization step of porphyrin synthesis via mechanochemistry. Using the method of ball-mill grinding an equimolar amount of pyrrole and an aldehyde in the presence of an acid catalyst followed by oxidation of the intermediate yields an amount of tetraphenylporphyrin similar to amounts obtained through traditional synthesis. UV-Vis spectroscopy and <sup>1</sup>H Nuclear Magnetic Resonance spectroscopy have been used to confirm the yields and purity of synthesized porphyrins. Through the use of mechanochemical synthetic protocol, it was possible to isolate yields and characterize a series of tetra-aryl and tetra-alkyl-substituted porphyrins, including some that are usually difficult to obtain from in-solvent synthesis. This study shows that applying mechanochemistry can provide access to porphyrins in yields as good as or better than those obtained in solution-without need for solvent in the cyclization step.

Series of meso-tetrasubstituted porphyrins synthesized using mechanochemistry

249th National Meeting (2015)

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