BILANES, BILENES, AND RELATED SUBSTANCES 



LS7 



about —2 (474).* Lacking tertiary nitrogens they form no complex 

 salts. They are easily autoxidizable. On condensation with p-i\'\- 

 methylaminobenzaklehyde they are converted into red pigments. 

 The nature of this "Ehrlich aldehyde reaction" is not yet under- 

 stood (861, p. 716). 



TABLE VIII 



Urobilinogens and Urobilins 



Mesohilane 



Tetrahydro- 

 mesobilane 



Mesobilene-(b) 



Tetrahydro- 

 mesohilene-(b) 



M K M p P M M E 



H Ht H H« M Ht H 



,MEMP PMME, 



H Hi H Hg H H« H 



ME M P P_M M E 



H H« H H Hj H 

 jjM E M F P M M E_jj 



H H2 H H H« H 



? 



Mesobilirubinogen (leuco 

 compound of mesobili- 

 rubin and bilirubin) 

 "Urobilinogen" (normally 

 smaller part of uro- and 

 stercobilinogen) 



"Stercobilinogen" (nor- 

 mally larger part of 

 uro- and stercobilino- 

 gen) 



"Urobilin-IXa" (normally 

 smaller part of uro- and 

 stercobilin) 



"Stercobilin" (normally 

 larger part of uro- and 

 stercobilin, levorota- 

 tory) 



rf-Urobilin (dextrorota- 

 tory) 



The autoxidation of bilanes leads to the corresponding bilenes-(b), 

 urobilinoid pigments. The correct formula for mesobilene-(b) was 

 suggested by Lemberg (1677,1678) on the basis of the fact that 

 ferric chloride oxidation yielded bilatriene but not biladiene-(a,c) 

 (rubin), which contains methylene in the b position, and also on the 

 basis of their similarity to pyrromethenes. The structure was finally 

 established by the synthesis of mesobilene-(b) ("urobilin IXa") by 

 Siedel (2550) from formylneobilirubinic acid and isoneobilirubinic 

 acid (Fig. 23). 



Ferric chloride oxidizes mesobilene-(b) to mesobilierythrin, meso- 

 bili violin, and mesobiliverdin (1677,1680,1690), while nitric acid 



*This association of pyrrole with proton must be distinguished from the dissocia- 

 tion of pyrrole as proton donor with a pK value of 16 {cf. Chapter III, Section 3.2.). 



