3 ^-CAROTENE 135 



Properties 



Crystalline form: Dark violet hexagonal prisms from benzene-methanol. Red, 

 rhombic, almost quadratic plates from petroleum ether. 



Melting point: 181-182° (corr.)^^; 181-182° (uncorr., Karrer and co- 

 workers^"); 183° (corr., evacuated capillary, Kuhn and Brockmann^^) ; 187.5° 

 (Miller92)_ 



Solubility: j8-Carotene is less soluble than the a-isomer, so that the latter is 

 concentrated in the mother liquors during the crystallisation of carotene. 

 ^-Carotene is easily soluble in carbon disulphide, benzene and chloroform, and 

 fairly easily soluble in ether and petroleum ether. 100 ml of w-hexane dissolve 

 109 mg of ^-carotene at 0°. The pigment is almost insoluble in ethanol and 

 methanol. 



Spectral properties: 



Solvent: Absorption maxima: 



Carbon disulphide 520 485 450 m/z 



Chloroform 497 466 m/x 



Petrol 483.5 452 426 m/x 



Hexane 477 450 425 m^ 



(cf. Fig. 6, p. 350 and Fig. 31, p. 361) 



Quantitative extinction measurements: Hausser and Smakula'^. 

 Raman spectrum: von Euler and Hellstrom^*. 



Colour reactions: On dissolving 1-2 mg of ^-carotene in 2 ml of chloroform and 

 adding concentrated sulphuric acid, the acid layer is coloured blue. On dissolving 

 the pigment in chloroform and adding one drop of fuming nitric acid, an immediate 

 blue colouration is first produced which then turns green and finally dirty yellow. 

 On dissolving 1-2 mg of /3-carotene in chloroform and adding a solution of antimony 

 trichloride in chloroform a dark blue colouration is produced which has an ab- 

 sorption maximum at 590 m/z. a-Carotene behaves differently; cf. von Euler, 

 Karrer and Rybdom®^. 



Hydrogen chloride in ether or methanol solution produces no colouration. 

 (For further data, see Zechmeister^^)^ 



Optical activity: j3-Carotene has a symmetrical structure and is optically 

 inactive. 



Partition test: On partition between petroleum ether and 90% aqueous 

 methanol, the concentration of j3-carotene in the former is 660 times as great 

 as in the latter (Kuhn and Brockmann^'). 



Chromatographic properties: ^-Carotene is fairly strongly adsorbed on cal- 

 cium hydroxide from petroleum ether solution. It is found below y-carotene 

 and above a-carotene on the chromatographic column^^. Elution can be effected 



References p. 165-ijo. 



