PORPHYRINS WITH TWO CARBOXYLIC ACID GROUPS 61 



by precipitation of the insoluble potassium salt and crystallization from 

 formic acid-methyl alcohol {1122). Protoporphyrin crj'stallizes in several 

 forms {2247), but this is due to the presence of impurities in some prepara- 

 tions (885,1121). 



Protoporphyrin in solution is rather unstable, particularly if 

 exposed to light. From solutions in dilute hydrochloric acid, it is 

 extracted with chloroform. Potassium and sodium salts are only 

 slightly soluble. The melting point of its dimethyl ester was found to 

 lie between 225 and 230° C. 



3.3.3. Deuteroporphyrin IX. C2oH6N4(CH3)4(H)2(CH2CH2C02H)2. 



Deuteroporphyrin was first observed by Schumm {2497,2501,2504; 

 2510) in feces after hemorrhage into the gastrointestinal tract or after 

 ingestion of a diet containing blood. Schumm found it to differ from 

 coproporphyrin and called it copratoporphyrin, but Fischer's name 

 deuteroporphyrin was later generally accepted. It is also found in 

 putrefying meat and in blood after prolonged alkaline putrefaction 

 (851). By heating hemin in resorcinol, the two vinyl groups are 

 removed and the deuterohemin thus formed can be readily con- 

 verted to deuteroporphyrin (837,2505). In contradistinction to 

 coproporphyrins, deuteroporphyrin is extracted by chloroform from 

 its solution in 0.2% hydrochloric acid; it forms an insoluble sodium 

 salt. The melting point of its dimethyl ester is 224° (496). Its 

 synthesis and transformation into hemin has been described in 

 Section 2. 



3.3.4. Hematoporphyrin IX. C2oH6N4(CH3)4(CHOHCH3)2(CH2- 

 CH2C02H)2. Although probably not of biological importance, 

 hematoporphyrin has played an important historical role (compare Sec- 

 tion 1). It is formed from hemin by the action of hydrobromic 

 acid in glacial acetic acid (2032-2034)- In this process as well as 

 during the action of concentrated sulfuric acid on hemoglobin or 

 hemin (Hoppe-Seyler), one molecule of water is added to each of 

 the two vinyl groups, transforming them into a-hydroxyethyl groups 

 — CH(0H)CH3. Since two optically active centers are created 

 by this reaction, hematoporphyrin may be a mixture of diastereo- 

 isomeric forms. Its synthesis from deuteroporphyrin IX and trans- 

 formation into protoporphyrin and hemin have been described in 

 Section 2.4. 



The occurrence of hematoporphyrin in nature has so far not been estab- 

 lished; it is not impossible, however, that hematoporphyrin or similar por- 



