CAROTENOLS AND OXYCAROTENOLft OP THE C40 SERIES 583 



ISIyxoxanthophyll can be ciystallized from acetone in violet needles which 

 melt at 182°C. It is markedly levo-rotatory ([ajcd = ~'255°C.)et}ianoi. 

 The pigment dissolves readily in pyridine and ethanol, but it is somewhat 

 less soluble in chloroform and acetone. It is insoluble in petroleum ether, 

 diethjd ether, and benzene. Myxoxanthophyll tetraacetate, C48H64OU, 

 forms glistening violet leaflets which melt at 131 J32°C\ 



{17) Rhodoviolascin and Related Pigments 



As early as 1873, Lankester first investigated the nature of the pigment in 

 purple bacteria. '*-" However, it was not until the studies of Karrer and his 

 associates'*^ that the composition of these pigments was clarified. The 

 most interesting chromogen identified was rhodoviolascin, which was pre- 

 pared both from Rhodovibrio species and from Thiocystis (sulfur bac- 

 teria). ^'^'^^'"'^^ Rhodoviolascin has an empirical formula of C42H60O2. 

 On catalj'tic hydrogenation it takes up 13 moles of hydrogen. According 

 to the absorption spectrum, it is apparent that all double bonds are in con- 

 jugation with each other. Neither of the original ionone rings is intact. 

 Moreover, it is the only known carotenoid containing methoxy groups. 

 There are two such groups in rhodoviolascin. There are no ketone groups, 

 and consequently the pigment does not react wuth hydroxylamine. 



CH30 



Rhodoviolascin 



When rhodoviolascin was subjected to stepwise degradation with per- 

 manganate, Karrer and Koenig^*^ were able to identify at least six products. 

 Bixin dialdehyde was one of the compounds isolated and identified. 



Rhodoviolascin separates from benzene in dark red, glistening crystals 

 which are spindle-shaped and which melt at 218°C. It is very difficultly 

 soluble in petroleum ether, ligroin, or methanol, but it dissolves somewhat 

 better in hot benzene. Its behavior is epiphasic. 



a. Rhodopin, C40H58O. Karrer and Solmssen^'^ were the first to iso- 

 late rhodopin from the "purple" bacterium, Rhodovibrio. ^^'^•^^^~^^^ It pre- 

 sumably contains 12 double bonds, all of which are conjugated, and a single 



'«'''• E. R. Lankester, Quart. J. ^ficroscop. Set., n.s., 13, 408-425 (1873); 16, 27-40 

 (1876). 



3" P. Karrer and U. Solmssen, Helv. Chim. Acta, 18, 1306-1315 (1935). 



»»* P. Karrer and U. Solmssen, Helv. Chim. Acta, 19, 3-5 (1936). 



^ P. Karrer, U. Solmssen, and H. Koenig. Helv. Chim. Acta, 21, 454-455 (1938). 



^^ P. Karrer and H. Koenig, Helv. Chim. Acta, 23, 460-463 (1940). 



