Synthesis of substituted porphyrins

✍ Scribed by D.O. Cheng; Eugene LeGoff

• Publisher: Elsevier Science
• Year: 1977
• Tongue: French
• Weight: 257 KB
• Volume: 18
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)93077-1

✦ Synopsis

We have found that octasubstituted porphyrins having no substituents in the meso positions can be prepared in high yields by acid catalyzed condensation of formaldehyde with a variety of 3,4-disubstituted pyrroles. This improved procedure circumvents the need to prepare aldehyde, aminomethyl, or hydroxymethyl pyrrole precursors and gives higher yields than previously reported procedures involving formaldehyde and 3,4_dimethylpyrrole and 3,4-diphenylpyrrole.'

The reactions are carried out by refluxing for several hours an ethanolic solution of a 3,4-disubstituted pyrrole with an excess of formaldehyde and a strong acid such as hydrobromic or hydrochloric acids. The reactions mixtures are allowed to stand exposed to the air for periods of a few days to several weeks. Slow oxidation in this way gives somewhat better yields than procedures involving bubbling air through the reaction mixture.