Tetraphenylporphyrin

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Tetraphenylporphyrin
Lewis structure for meso-tetraphenylporphyrin
Identifiers
CAS number 917-23-7 YesY
ChEMBL CHEMBL436524 N
Properties
Molecular formula C44H30N4
Molar mass 614.74 g/mol
Appearance dark purple solid
Density 1.27 g/cm3
Solubility in water insoluble in water
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Tetraphenylporphyrin, abbreviated TPP or H2TPP, is a synthetic heterocyclic compound that resembles naturally occurring porphyrins. Porphyrins are dyes and cofactors found in hemoglobin and cytochromes and are related to chlorophyll and vitamin B12. The study of naturally occurring porphyrins is complicated by their low symmetry and the presence of polar substituents. Tetraphenylporphyrin is hydrophobic, symmetrically substituted, and easily synthesized. The compound is a dark purple solid that dissolves in nonpolar organic solvents such as chloroform and benzene.

Synthesis and structure[edit]

Tetraphenylporphyrin was first synthesized in 1935 by Rothemund, who caused benzaldehyde and pyrrole to react in a sealed bomb at 150 °C for 24 h.[1] Adler and Longo modified the Rothemund method by allowing benzaldehyde and pyrrole to react for 30 min in refluxing propionic acid (141 °C) open to the air:[2]

8 C4H4NH + 8 C6H5CHO + 3 O2 → 2 (C6H5C)4(C4H2N)2(C4H2NH)2 + 14 H2O

Despite low yields, the synthesis of H2TPP is a common experiment in university teaching labs.[3][4]

The conjugate base of the porphyrin, TPP2-, belongs to the symmetry group D4h while its hydrogenated counterpart H2(TPP) is D2h.[5] Unlike natural porphyrins, H2TPP is substituted at the oxidatively sensitive "meso" carbon positions, and hence the compound is sometimes called meso-tetraphenylporphyrin. Another synthetic porphyrin, octaethylporphyrin (H2OEP) does have a substitution pattern that is biomimetic. Many derivatives of TPP and OEP are known, including those prepared from substituted benzaldehydes. One of the first functional analogues of myoglobin was the ferrous derivative of the "picket fence porphyrin," which is structurally related to Fe(TPP), being derived via the condensation 2-nitrobenzaldehyde and pyrrole.

A picket-fence porphyrin complex of Fe, with axial coordination sites occupied by methylimidazole (green) and dioxygen (R = amide groups).[6]

Sulfonated derivatives of TPP are also well known to give water-soluble derivatives, e.g. tetraphenylporphine sulfonate:

4 SO3 + (C6H5C)4(C4H2N)2(C4H2NH)2

→ (HO3SC6H4C)4(C4H2N)2(C4H2NH)2 + 4 H2O

Complexes[edit]

Complexation can be thought of as proceeding via the conversion of H2TPP to TPP2-, with 4-fold symmetry. The metal insertion process proceeds via several step, not via the dianion. The resulting complexes are symmetrical with simple NMR or EPR spectra.[citation needed] For example, Cu(TPP) has D4h symmetry. The corresponding iron complexes are more complex owing to variable oxidation states and coordination numbers. Well-studied derivatives include the ferric compounds, e.g. Fe(TPP)Cl and the oxide [Fe(TPP)]2O, and ferrous compounds, e.g. Fe(TPP)CO(L) (L = imidazole, pyridine).

Optical properties[edit]

Optical properties of tetraphenylporphyrin in toluene

Tetraphenylporphyrin has a strong absorption band with maximum at 419 nm (so called Soret band) and four weak bands with maxima at 515, 550, 593 and 649 nm (so called Q-bands). It shows red fluorescence with maxima at 649 and 717 nm. The quantum yield is 11%.[7]

Applications[edit]

H2TPP is a photosensitizer for the production of singlet oxygen.[8]

References[edit]

  1. ^ P. Rothemund (1936). "A New Porphyrin Synthesis. The Synthesis of Porphin.". J. Am. Chem. Soc. 58 (4): 625–627. doi:10.1021/ja01295a027. 
  2. ^ A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J. Assour and L. Korsakoff (1967). "A simplified synthesis for meso-tetraphenylporphine". J. Org. Chem. 32 (2): 476–476. doi:10.1021/jo01288a053. 
  3. ^ Falvo, RaeAnne E.; Mink, Larry M.; Marsh, Diane F. "Microscale Synthesis and 1H NMR Analysis of Tetraphenylporphyrins". J. Chem. Educ. 1999 (76): 237. doi:10.1021/ed076p237. 
  4. ^ Girolami, G. S.; Rauchfuss, T. B.; Angelici, R. J., Synthesis and Technique in Inorganic Chemistry, University Science Books: Mill Valley, CA, 1999.ISBN 0935702482
  5. ^ Moghadam; et al. (January 2012). "C o mputing Group Theory and Character Table of Non Rigid Tetraphenylporphyrin H2 (Tpp) and Metalloporphyrin Mii (Tpp)". Glo ba l Journal of Science Frontier Research Chemistry 12 (1). 
  6. ^ S. J. Lippard, J. M. Berg “Principles of Bioinorganic Chemistry” University Science Books: Mill Valley, CA; 1994. ISBN 0-935702-73-3.
  7. ^ J. B. Kim, J. J. Leonard and F. R. Longo (1972). "A mechanistic study of the synthesis and spectral properties of meso-tetraphenylporphyrin.". J. Am. Chem. Soc. 94 (11): 3986–3992. doi:10.1021/ja00766a056. 
  8. ^ Karl-Heinz Pfoertner "Photochemistry" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a19_573