Synthesis of meso-TPP Revisited: Its “Green-Oriented” Optimization Under Controlled Microwave Heating

Abstract

A practical and proecological improvement for synthesis of meso-tetraphenylporphyrin (meso-TPP) under microwave irradiation is described. A cyclocondensation reaction of benzaldehyde and pyrrole followed by oxidation of the porphyrinogen formed as an intermediate in a small amount of propionic acid at 120 °C (under controlled microwave heating) resulted in conversion to meso-TPP in a reasonable yield (ca. 30%) in preparative-scale experiments (300–500 mg). The influence of many parameters such as the concentration of reagents, catalyst, solvent, temperature, reaction time, and oxidant on the reaction yield was studied. The environmental motive in this improvement is reduction of solvent volume (ca. 250 times). Also, some toxic reagents were eliminated from the procedure.

Keywords:

• Green chemistry
• microwave-assisted synthesis
• optimization
• porphyrins

ACKNOWLEDGMENT

This work was supported by the Ministry of Science and Higher Education, Grant N N204 218535 (2008–2011).

Notes

^a Concentration is given in millimoles [mmol] per 1 mL of the solvent (in all tables and in Experimental Section).

^b The reaction conditions in which the greatest yields of meso TPP were obtained are marked in gray (in all tables).

^c Under the reaction conditions described in the literature.^{[ 8 ]}