18 



VITAMINS A AND CAROTENES 



which are highly labile and rearrange in the presence of traces of acids to 

 monofuranoxides. These changes may be illustrated as follows: 



CHa 



CHo 



CHa 



C 



/ \ I 

 H2C C— CH=CH— C 



I II 



H2C C CH3 



\ / 



c 

 H2 



CH3 



I 



C— CH=CH— C 



CH3 CHj 

 \ / 



c 



CH2 



CH3— C CH2 



\ / 



c 

 H2 



i8-Carotene (skeleton) + monoperphthalic acid 



i 

 CH3 CH3 CH3 CHj 



\ / \ / 



C CH3 CH3 c 



/ \ I 



H2C C— CH=CH— C 



\ 



o 

 / 



H2C C— CH3 CH3— c 



CH3 



I 



C— CH=CH— C 



\ / 



c 

 H2 



CHj CH3 



c 



CH2 

 CH2 



H2C 

 H2C 



\ 



c 

 H2 



o 



XXI /3-Carotene monoepoxide 

 H+ 



CH3 

 \ 

 =CH CH3 CH3 



II I / 



CH— C C— CH=CH— C 



CH3 



CH, 



CH, 



CH3 — C CHj 



\ / 

 C 

 H2 



XXII /3-Carotene monofurarioxide (mutatochrome) 



Similarly jS-carotene forms a diepoxide (XXIII) which rearranges on one 

 side to give luteochrome (XXIV, /3-carotene monoepoxide monofuranoxide) 

 or on both sides to give aurochrome (XXV, ;Q-carotenc difuranoxide). 

 a-Carotene does not form a diepoxide. When /S-carotene is carefully treated 



" P. Karrer, Fortschr. Chem. org. Naturstoffe 5, 1 (1948). 



