lo FUCOXANTHIN 311 



QoHeoOe- The nature of the oxygen atoms in fucoxanthin has not yet been clari- 

 fied. The results obtained by Karrer and co-workers*^ indicated 4-5 hydro xyl 

 groups, whereas the results of Kuhn and Winterstein^^ indicated 6. On 

 catalytic hydrogenation 10 mols of hydrogen are absorbed*^ ; but the analysis 

 of the perhydrocompound gave values in agreement with the formula C^oHygOg*". 

 On vigorous oxidation with permanganate, four mols of acetic acid are 

 obtained. From these results the number of side-chain methyl groups can be 

 deduced. From the oxidation products of the pigment with alkaline per- 

 manganate, a : a-dimethylmalonic acid can be isolated (Karrer and co- 

 workers^i). The fact that no a : a-dimethylsuccinic acid or a:a-dimethylglutaric 

 acid are formed indicates that the two ends of the fucoxanthin molecule are 

 highly substituted by hydroxyl groups (cf. p. 201). 



These results do not, however, lead to any definite constitution for the 

 pigment. 



Heilbron and Phipers*" proposed the following formula for fucoxanthin. 



CH3 CH3 CH3 CH3 



C CH3 CH3 CH3 CH3 C 



/\ \ \ \ \ /\ 



CHa CO-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-CO CHj 



HOCH CH-OH HO-CH HCOH 



\y\ Fucoxanthin(?) /\/ 



CHg CH3 CH3 CHj, 



The proposed constitution is not, however, in accord with all the properties 

 of fucoxanthin. The chromophoric system of the proposed structure corresponds 

 to that of j3-carotenone (cf . p. 141) and the absorption maxima would be expected 

 to be located at considerably longer wavelengths than those observed. Further- 

 more, a diketone of this type should be reduced by zinc and acetic acid to a 

 dihydro-derivative, as in the caseof j8-carotenone. Fucoxanthin does not undergo 

 such a reaction. The proposed formulation of the pigment is thus unacceptable. 



Properties 



Crystalline form: Fucoxanthin crystallises from methanol in brown-red 

 prisms with a blue lustre. The crystals contain 3 molecules of methanol of cry- 

 stallisation. From dilute ethanol or acetone, the pigment is obtained in deep 

 red hexagonal plates containing 2 molecules of water. From a mixture of ether 

 and petroleum ether, the pigment crystallises in needles without solvent of 

 crystallisation. 



Melting point: 159.5-160.5° (corr., Wilstatter and Page^^), 166-168° 

 (uncoir.)*". 

 References p. 341-343. 



