The synthesis of meso-substituted porphyrins: reaction conditions and substituent effects
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The purpose of this study is to gain a better understanding of the parameters governing the synthesis of meso-substituted porphyrins. As a result of doing so, we anticipate that better reaction conditions can be developed, which will afford porphyrins in higher yields. Porphyrins are a large class of deeply colored red or purple, fluorescent crystalline pigments, of natural or synthetic origin, having in common a substituted aromatic macrocyclic ring consisting of four pyrrole-type residues, linked together by four methine bridging groups. The structure of porphyrin has been known since the early 1900's, but discrepancies exist on how the formation of porphyrin actually occurs. Several methods have been developed for the porphyrin reaction under various conditions. Three of the most common methods for the synthesis of meso-substituted porphyrins are: the Rothemund Method, the Adler Method, and the Lindsey Method. The conditions for these reactions vary from the harsh conditions where the reaction is completed in 15 minutes to 1 hour. Although each of these methods has their advantages, a convenient procedure for the large-scale synthesis of meso-substituted porphyrins has yet to be developed. Therefore, the demands required by commercial enterprise to prepare new molecules and materials in sufficient quantities as to make their use practical have still not been met. As a result, this led to the investigation of the 2-step, 1-pot synthesis and the proposal of a 2-step, 2-pot synthesis of porphyrins whereby the porphyrinogen intermediate is isolated and oxidized to porphyrin under non-reversible conditions.