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tpp synthesis.docx - Bryanna Tanase John Torres Geoffrey...

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Bryanna Tanase John Torres Geoffrey Gray Preparation of meso -tetraphenylporphyrin and metalloporphyrin
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Introduction Porphyrins are brightly colored cyclic compounds consisting of four pyrrole rings linked together through methene (-H=C) bridges 2 . Pyrrole is a compound made up of a cyclopentadiene ring with a nitrogen atom inserted into it 2 . The four pyrrole rings are usually surrounded by a metal atom. Porphyrins, are aromatic compounds because they have a Huckle number of pi electrons (4n+2) 2 . Tetraphenylporphyrin, for example, is aromatic because it has 46 pi electrons, this is a Huckle number of pi electrons where n=11. The aromaticity and alternating single double bonds of porphyrins is what gives them a bright color 2 . An example of a pyrrole molecule and porphyrin are shown below in Figure 1. Porphyrins are made by reacting pyrrole with benzaldehyde 1 . Figure 1: Pyrrole and porphyrin 2
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Porphyrins are a part of many vital processes in nature and biological systems including electron transfer, oxygen transport, conduction of energy for photosynthesis, and conversion of carbon dioxide into fuel 2 . Metalloporphyrins are porphyrin derivatives in which a metal ion is inserted into the middle of the ring 1 , and they also have important roles as intermediates in the catalytic cycles of heme proteins as well as photosynthesis 2 . Some of the most well known metalloporphyrins include heme (iron atom inserted ) which is a part of the molecule hemoglobin found in red blood cells 3 , and chlorophyll (magnesium atom inserted) which is the photosynthetic pigment found in the chloroplasts of plants 3 . An image of the heme molecule is provided below in Figure 2. Figure 2: heme structure 2 The reaction that produces Tetraphenylporphyrin in this experiment is between benzaldehyde and pyrrole with acidic acid as a solvent and heat which is used to promote the reaction. The nucleophile in this reaction is pyrrole because it donates a pair of electrons from its
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pi system to benzaldehyde to form a new bond in between the two compounds. The electrophile in this reaction is benzaldehyde because it receives a pair of electrons from pyrrole in order to create a new covalent bond. The objective for this experiment is to synthesize meso-tetraphenylporphyrin from the reaction of four moles of pyrrole and four moles of benzaldehyde. In the first step of the reaction, a molecule of pyrrole attacks benzaldehyde using one of its five bonds, which causes the electrons that are part of benzaldehyde’s carbonado Group to be pushed up and attack the hydrogen atom from acetic acid, forming the compound 2-(hydroxy(phenyl)methyl)-2,3-dihydro- 1 H -pyrrol-3-ylium and leaving behind an acetate anion. The acetate then deprotonates the  aforementioned compound which creates phenyl(1 H -pyrrol-2-yl)methanol. The alcohol on this 
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