Synthesis of Tetraphenylporphin: A Convenient Undergraduate Organic Laboratory Experiment Porphyrins are a class of biologically important water-soluble, nitrogen-containing pigments exemplified by, among others, the chlorophylls and hemoglobins. The parent ring structure of the parphyrins is that of the modified tetrapyrrole, porphin. There are no porphyrin-related syntheses in the current organic laboratory texts-even though these materials are intriguing to the typical student.' The present, easy to perform experiment should help ta rectify that situation. Individual instructors may wish to pursue this area further and, for example, incorporate various metals into the porphin framework.2
QI + ,,,, CHrC",CO1X hen*
meso-tetmphenylporphii
H
pyrrble
benraldehyde
Freshly distilled3 pyrrole (5.6 ml, 0.08 mole) and 8 nil (0.08 male) of reagent grade benzaldehyde are added to 300 ml of refluxingreagent grade propionicacid. Take c a r e t o n e i t h e r breathe n o r get any of t h e liquid reagents on t h e skin. Pyrrole may a c t a s a poison to t h e nervous system. If the experimental setup cannot be set in a fume hood, be sure to add a noxiowgas trap to the tap ofthe reflux condenser. After refluxing for 30 min, the solution is cooled to roam temperature and filtered (the filter cake should be washed thoroughly with methanol). The resultant lustrous purple crystals of mesotetraphe'nylporphin4are more than 97% pure. An interesting note is made on these materials in Lehman, J. W., "Operational Organic Chemistry," Allyn and Bacon, Inc., Boston, 1981, p. 116. Falk, J. E., "Porphorins and Metalloporphyrins", Elseview Publishers, Amsterdam London and New York, 1964. Vacuum distillation is preferred although the results of the experiment are still acceptable even if the pyrrole is purified by simple distillation. Adler, A. D., et al., J. Org. Chem.,32,476 (1967). Craig L. Hill Richard E. Bozak California State University Hayward Hayward, CA 94542
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Journal of Chemical Education
University of California. Berkeley Berkeley. CA 94720
