5 ASTACENE AND ASTAXANTHIN 239 



workers^^ prepared astacene dipalmitate from astacene and palmitic acid 

 chloride. The ester crystalHses from petroleum ether in almost rectangular red 

 leaflets, m.p. 121°. Astacin dipalmitate exhibits epiphasic properties. 



Properties and Derivatives of Astaxanthin 



Crystalline form: Astaxanthim crystallises from pyridine in lustrous plates. 



Melting point: 216° (with decomposition). 



Solubility: Only few data are recorded in the literature regarding the 

 solubility of astaxanthin. The pigment is readily soluble in pyridine, from which 

 it can be crystallised on addition of water. 



Spectral properties (cf. Fig. 15, p. 354) : In contrast to astacene, astaxanthin 

 exhibits an absorption curve in which three definite maxima can be recognised^^. 

 In pyridine, these maxima are located at 476, 493 and 513 m^^^. 



Optical activity: Astaxanthin is optically inactive^*. 



Partition test: Astaxanthin exhibits entirely hypophasic properties. 



Chromatographic behaviour: Kuhn and co-workers chromatographed asta- 

 xanthin on cane sugar from a mixture of benzene and petroleum ether (1:4). 

 Benzene was employed for elution. 



Colour reactions: The alkali salts of the pigment have a characteristic deep- 

 blue colour which is only shown, however, if air is excluded. On admission of 

 oxygen, there is an immediate colour change to red and dehydrogenation to 

 astacene occurs. 



Detection and estimation: Astaxanthin can be readily identified by the 

 colour reactions described above. 



Astaxanthin diacetate C44H5gOg^^ : 



CHo CHo CHo CHo 



C CH3 CH3 CHo CH3 C 



/\ I I I I /\ 



CH2 C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CH^ 



I II II L 



CH3COOCH C-CHj HjC-C CH-ooc-ce3 



\^ / . Astaxanthin diacetate \^ / 



CO CO 



The diacetate is obtained by treating astaxanthin dissolved in pyridine 

 with acetic anhydride. The ester crystallises from a mixture of pyridine and 

 water in rugged, deep blue-black needles, m.p. 203-205° (Berl-Block, in vacuum, 

 uncorr.). The ester is very little enolised in the cold. In the partition test, it is 

 References p. 253—255. 



