58 



III. PORPHYRIN CHEMISTRY 



Corwin and co-workers have discovered a possible source of error in such 

 syntheses {493-4-9o). The condensation of a pyrrole a-aldehyde with an 

 a-unsubstituted pyrrole often does not proceed as simply as indicated in 

 step 1 of Figure 5. A tripyrrylmethane is formed first and this may after- 

 ward break down to symmetrical as well as to unsymmetrical py rromethene : 



pyrromethene A 

 H M 



.^, 



M 



H. 



symmetrical pyrromethene A' 



Fig. 6. Pyrromethene synthesis, according to Corwin ct ah (/t!).J-J,'.t')). 



Corwin and Krieble (490) confirmed, however, the structure of pyrro- 

 methene A and of deuteroporphyrin IX in spite of some divergent findings 

 on the melting point of pyrromethene A. A similar re-examination of the 

 structure of coproporphyrin III, which is based on evidence of the same 

 type, should be undertaken. Evidence on the unsymmetrical structure of 

 natural bile pigments derived from hemoglobin had also strongly supported 

 the unsymmetrical structure of hemin and the porphyrins derived from it 

 (c/. Chapter IV). 



3. INDIVIDUAL PORPHYRINS 



3.1. Porphin, C2oH6N4(H)8 



Porphin was first prepared by Fischer and Gleim (818), by boiling 

 pyrrole-a-aldehyde with formic acid and alcohol, later by Rothemund 

 {2352,2353) by condensation of pyrrole with formaldehyde. The 



