60 III. PORPHYRIN CHEMISTRY 



Mesoporphyrin dimethyl ester is obtained in 60% yield, if hemin is 

 heated with hydrazine hydrate in pyridine and the mixture is then 

 heated with methyl alcoholic hydrogen chloride. Mesohemin can be 

 prepared from hemin in a similar way with still better yield (817). 

 Finally formic acid and colloidal palladium can be used for the prepa- 

 ration of mesoporphyrin from hemin (535,867,2749).* The melting 

 point of the dimethyl ester is 216° C. The sodium salt of mesopor- 

 phyrin is insoluble in aqueous alkali and this property is used for the 

 purification. Mesoporphyrin IX occurs naturally in human feces 

 (3170). 



3.3.2. Protoporphyrin IX. C2oH6N4(CH3)4(C2H3)2(CH2CH2C02H)2. 



Hoppe-Seyler recognized that reduced hemoglobin yielded porphyrin 

 much more readily on treatment with acids than oxyhemoglobin. 

 While Laidlaw (163.2) prepared protoporphyrin from blood after 

 bacterial reduction, but failed to recognize the difference of this por- 

 phyrin from hematoporphyrin, it was not until Schumm and his 

 co-workers (209 8, 2 100, 2 1^9 3, 2 If9 6) had carried out their spectroscopic 

 investigation that the diflFerence between these two compounds was 

 recognized. Meanwhile porphyrins differing in a similar way from 

 hematoporphyrin were found in the intestine in occult gastrointestinal 

 hemorrhage (Snapper's porphyrin) (2583), in putrefying blood 

 (Kjimmerer's porphyrin) (8 40,14-4^8, 14-4-9) and in birds' egg shells 

 (ooporphyrin) (841,842). Following Fischer and Schneller's crystal- 

 lization of Kammerer's porphyrin (875), Fischer established their 

 identity and renamed the porphyrin protoporphyrin (847) on account 

 of its close relationship to hemoglobin. 



For the preparation of protoporphyrin it is essential to avoid the attack 

 of strong acids or strongly reducing substances on the vinyl side chains. 

 Several workers {867,1282,1763,2102) have made use of the easier removal 

 of iron from reduced hemoglobin by acids for the purpose of preparing 

 protoporphyrin, the most recent modification being that of Grinstein and 

 Watson (1057). By similar methods the iron can be removed from pyridine 

 hemochromogen (81)7, 1121,2104) • Other methods of preparation include 

 the action of formic acid and iron powder on hemin (866) and the action of 

 stannous chloride on hematin prepared from blood with oxalic acid in acetone 

 (1121). A good method is the reduction of hematin in acid solution by sodium 

 amalgam (Schumm, 2406,2502). 



The crude porphyrin is purified by crystallization from pyridine-petroleum 

 ether (Wo7, 1115, 1121), by chromatography of the dimethyl ester solution 

 in chloroform-petroleum ether on alumina or calcium carbonate (1057), or 



*Also from protoporphyrin H95a). 



