REFERENCES 165 



Pro-y-carotene is a naturally occurring stereoisomer of y-carotene. According 

 to Zechmeister and Schroeder^^^ 6 or 7 of the double bonds have a trans, 

 and 4 or 5 a cis configuration. By the fusion of pro-y-carotene crystals, by 

 heating solutions of the pigment, or by treatment with concentrated hydro- 

 chloric acid or iodine, a mixture of stereoisomers is obtained which contains 

 y-carotene. 



Pro-y-carotene crystallises from a mixture of benzene and methanol in 

 glistening redplates,m.p. 118-119° (corr.) (cf. Zechmeister and Schroeder)^^^^ 

 It is easily soluble in benzene, petroleum ether and other organic solvents, with 

 the exception of alcohols. 



Solvent: Absorption maxima 



Carbon disulphide 493.5 460.5 m/x 



Benzene 477 447.5 m/j. 



Chloroform 473 (444) m/i 



Ethanol (465) (437) m/x 



Petroleum ether 464 (435) mfi 



Pro-y-carotene is adsorbed a little more weakly than y-carotene on calcium 

 hydroxide from petroleum ether solution. 



REFERENCES 



1. Hartsen, Chem. Centr. 1S73, 204; Compt. rend 76 (1873) 385; Courchet, Ann. Sci. nat. 

 (7) 7 (1888) 320, 356. 



2. MiLLARDET, Bull. Soc. Sci. Nuncy (2) / (1875) p. 21. 



3. C. A. ScHUNCK, Proc. Roy. Soc. (London) 72 (1903) 165 (cf. Zopf, Biol. Zentralbl. 15 

 (1895) 417. 



4. R. WiLLSTATTER and H. H. Escher, Z. physiol. Chem. 64 (1910) 47. 



5. P. Karrer and co-workers, Helv. chim. Acta 11 (1928) 751; 12 (1929) 285; 11 (1928) 

 1201; 13 (1930) 1084; 14 (1931) 435- 



6. R; Kuhn and C. Grundmann, Ber. 65 (1932) 898, 1880. 



7. R. WiLLSTATTER and H. H. Escher, Z. physiol. Chem. 64 (1910) 47- 



8. R. Kuhn and C. Grundmann, Ber. 65 (1932) 1880. 



9. L. Zechmeister and L. v. Cholnoky, Ber. 63 (1930) 422. 



10. R. WiLLSTATTER and H. H. Escher, Z. physiol. Chem. 64 (1910) 47. 



11. P. Karrer and R. Widmer, Helv. Chim. Acta 11 (1928) 751. 



12. R. Pummerer, L. Rebmann and W. Reindel, Ber. 62 (1929) 141 1. 



13. P. Karrer and W. E. Bachmann, Helv. Chim. Acta 12 (1929) 285. 



14. P. Karrer, A. Helfenstein, B. Pieper and A. Wettstein, Helv. Chim. Acta 14 



(1931) 435- 



15. P. Karrer, A. Helfenstein, H. Wehrli and A. Wettstein, Helv. Chim. Acta 13 

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16. P. Karrer, A. Helfenstein, H. Wehrli and A. Wettstein, Helv. Chim. Acta 13 



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17. P. Karrer, A. Helfenstein and R. Widmer, Helv. Chim. Acta 11 (1928) 1201. 



18. P. Karrer, A. Helfenstein, B. Pieper and A. Wettstein, Helv. Chim. Acta 14 



(1931) 435- 



19. R. Kuhn and A. Winterstein, Ber. 65 (1932) 1873. 



