222 CAROTINOIDS AND RELATED PIGMENTS 



Kohl (1902b), using a Zeiss spectroscope, obtained the measure- 

 ments shown in Table 16, using various solvents with different re- 

 fractive indices. The data also show the bands of solid carotin, 

 obtained by depositing a very thin layer of carotin crystals on one 

 side of a glass slide. 



Lycopin. This red isomer of carotin forms yellow solutions in hot 

 ether, chloroform, alcohol, benzene and petroleum ether. These solu- 

 tions have a somewhat brown tone in comparison with similar solu- 

 tions of carotin. Even saturated solutions of lycopin in these sol- 

 vents, with the possible exception of chloroform, contains much less 

 pigment than the corresponding solutions of carotin. This probably 

 accounts for their yellow color. Solutions of lycopin in carbon disul- 

 fide are characterized by their bluish-red color which persists even in 

 great dilution, while solutions of carotin in this solvent change to a 

 yellowish red color on great dilution. The effect of the addition of 

 mineral acids to alcoholic solutions of lycopin has not been investi- 

 gated. Lycopin, however, because of its great oxidizability reacts 

 toward ferric chloride like the other carotinoids. The relation of 

 lycopin toward adsorbents remains to be studied. 



Lycopin shows its hydrocarbon nature by exhibiting the same rela- 

 tive solubility properties as carotin when examined by the phase 

 test between petroleum ether and dilute alcohol, on the one hand, and 

 between dilute alcohol and carbon disulfide on the other hand. In 

 each case the pigment is found quantitatively in the petroleum ether 

 or carbon disulfide. 



TABLE 16. VISIBLE ABSORPTION SPECTRA OF CAROTIN IN VARIOUS SOLVENTS WITH 

 DIFFERENT REFRACTIVE INDEX (KOHL, 1902b) 



Refractive Position 0} bands 



Solvent Index Band I Band II Band III 



Alcohol ................. 1.358 (ave.) 490-475 455-445 430-418 



Ether .................... 1.357 490-475 455-445 430-418 



Acetone .................. 1.365 500-478 460-450 430-420 



Chloroform .............. 1.449 505-480 465-450 435-420 



Carbon tetrachloride ..... 1.460 507-480 466-452 435-420 



Carbon disulfide ......... 1.628 510-485 470-458 437-425 



Solid carotin ............ ? 550-530 495-480 460-450 



One of the most characteristic properties of lycopin solutions which 

 is especially serviceable for the identification of the pigment is the 

 position of the absorption bands. The relation of the lycopin spec- 

 trum in carbon disulfide to that of the other carotinoids in the same 

 solvent is shown in Figure 1, taken from the paper of Monteverde 



