154 CAROTENOID HYDROCARBONS OF KNOWN CONSTITUTION X 

 Melting point: 187-188° (corr.)i52_ 



Solubility: a-Carotene is considerably more soluble than the /^-isomer. It is 

 very soluble in carbon disulphide and chloroform, easily soluble in benzene and 

 ether, sparingly soluble in petroleum ether and almost insoluble in alcohols. 

 100 Ml of hexane at 0° dissolve 294 mg of a-carotene^^^. 



Spectral properties: 



Solvent: Absorption ynaxiina: 



Carbon disulphide . , 509 477 m/i 



Petrol 478 447.5 m^ 



Chloroform 485 454 m/i 



Hexane 475 445 420 395 m^ 



(cf. Fig. 7, p. 350 and Fig. 31, p. 361) 



For quantitative extinction measurements, see Hausser and Smakula^^*. 

 For Raman spectra, see von Euler and Hellstrom^^^. 



Colour reactions: a-Carotene in chloroform solution gives a blue colouration with 

 concentrated sulphuric acid. On adding antimony trichloride to a chloroform 

 solution, a deep blue colouration is produced with an absorption maximum near 

 542 m/i (Karrer and WalkerI^^j 



Optical activity: The specific rotation in benzene is +385° (643.85 m/^ cadmium 

 hne) (KuHN and Lederer^^'). The rotatory dispersion was determined by Karrer 

 and Walker152 • 



[a]j8 = 315° (±7°) [a]45 = +385° (±5°) 



Partition test: a-Carotene exhibits entirely epiphasic properties on partition 

 between petroleum ether and 90 % methanol. 



Chromatographic properties: a-Carotene is adsorbed less strongly than 

 j8-carotene on calcium hydroxide from petroleum ether solution, and is found 

 below /3-carotene on the column. (Karrer and Walker^^^). It can be eluted by 

 means of ether containing about 5 % methanol. 



Behaviour toivards oxygen: The oxidation of a-carotene in light is autocata- 

 lytic (BaurIS'). 



Detection and estimation: The separation of a-carotene from other caro- 

 tenoid hydrocarbons is effected by chromatographic adsorption on calcium 

 hydroxide. Its presence can be established by the determination of the ab- 

 sorption maxima. For the colorimetric estimation of the pigment, Kuhn and 

 Brockmann^^^ recommend an alcoholic solution of azobenzene as a standard. 



Physiological behaviour: a-Carotene exhibits strong vitamin A activity^^^. 

 References p. 165-ijo. 



