4 ZEAXANTHIN 185 



Optical activity: According to several workers, zeaxanthin, like ^-carotene, 

 is optically inactive. Recently, however, Zechmeister and co-workers^^ reported 

 that their zeaxanthin preparations have a rotation of [aj^^ = — 40-50° in 

 chloroform. Perhydrocarotene obtained by the reduction of perhydrozeaxanthin 

 dibromide, is optically inactive in contrast to the corresponding products from 

 xanthophyll. 



Partition test: Zeaxanthin exhibits entirely hypophasic character on parti- 

 tion between methanol and petroleum ether. 



Chromatographic behaviour: Zeaxanthin is easily adsorbed on calcium car- 

 bonate or zinc carbonate from benzene solution. 



Detection and estimations: Zeaxanthin can be separated from other phyto- 

 xanthins b}^ adsorption on zinc carbonate. It can be identified by its absorption 

 maxima, in conjunction with the partition test. According to Kuhn and 

 Brockmann the pigment can be determined colorimetrically, using a solution 

 of azobenzene in ethanol as a standard*". 



Physiological behaviour: Zeaxanthin exhibits no vitamin A activity, but it 

 yields an active product on treatment with phosphorous tribromide*^. 



Colour reactions: Zeaxanthin dissolves in concentrated sulphuric acid with 

 a fairly stable deep blue colouration. On treating a solution of the pigment in 

 chloroform with antimony trichloride a blue colouration is produced which has 

 been examined spectroscopically*^. 



Derivatives 



Perhydrozeaxanthin C4oH7g02.' Colourless, viscous oil*^-* which is leavo- 

 rotatory in contrast to perhydroxanthophyll. [aj^ = — 24.5^*^-* 



Zeaxanthinhalogenides: Karrer and co-workers** replaced the two hydroxyl 

 groups in perhydrozeaxanthin by bromine, thus obtaining 3:3'-dibromo- 

 perhydrozeaxanthin. On treating a solution of zeaxanthin with bromine, 8 

 mols of the halogen are absorbed. 



Zeaxanthin monomethyl ether €4^115802: This compound is formed on treating 

 zeaxanthin with the potassium derivatives of tertiary am.yl alcohol and methyl 

 iodide*^. It crystallises from methanol in needles, m.p. 153°. 



Zeaxanthin dimethyl ether C42H5QO2: This compound is obtained as by-product 

 in the preparation of the monomethyl ether*^. It crystallises from petroleum ether 

 in dark red needles, m.p. 176°. It is very sparingly soluble in methanol and ethanol. 



Zeaxanthin diacetate C44H60O4: Karrer and Solmssen obtained this ester by 

 treating a solution of zeaxanthin in pyridine with acetic anhydride*®. The diacetate 

 crystallises from a mixture of benzene and methanol. M.p. 154-155°. 



According to P. Karrer and co-workers, Helv. chim. Acta 15 (1932) 492, perhydro- 

 zeaxanthin is optically inactive. 



References p 214— 2iy. 



