136 CAROTENOID HYDROCARBONS OF KNOWN CONSTITUTION X 



by means of ether containing about 5 % methanol. jS-Carotene is only very 

 weakly adsorbed on zinc carbonate and calcium carbonate, and is washed 

 through during the development of a chromatogram on these adsorbents. 



Behaviour towards oxygen: On standing in air, carotene absorbs oxygen 

 with increasing rate with the formation of colourless products®^. According 

 to VON EuLER etc.^°° the autoxidation of very pure preparations only begins 

 after several days' contact with air, formaldehyde being formed^*'^. On shaking 

 a solution of j3-carotene in carbon tetrachloride in oxygen, a little glyoxal is 

 formed^°2. 



Detection and estimation: j3-carotene can be separated from the other caro- 

 tenoid hydrocarbons by chromatographic adsorption on calcium hydroxide 

 from petroleum ether. It is identified by its absorption maxima. According to 

 KuHN and Brockmann^"^ an alcoholic solution of azobenzene can be used as 

 standard for colourimetric determinations. 



Physiological behaviour: /3-Carotene possesses high vitamin A potency 

 which has been studied in detail by von Euler, Karrer and co-workers^"* 

 (cf. p. II). 



Derivatives 



^-Dihydrocarotene C40H58; 



CH, CH, CH3 CH3 



C CH3 CH3 CH3 CH3 C 



/\ II II /\ 



CH2 C-CH2CH=C-CH=CHCH=C-CH=CHCH=CH-C=CHCH=CH-C=CH-CH2-C CH^ 



CHj C-CH3 HgC-C CHj 



\ / /5-Dihydrocarotene \ y^ 



CHj CH2 



)3-Dihydrocarotene is formed together with other products by the reduction 

 of jS-carotene with aluminium amalgam^"^. Pure j8-dihydrocarotene was isolated 

 by Karrer and Ruegger^"^ using the refined chromatographic method of 

 separation. The constitution shown above was derived by these authors. 



Dihydrocarotene crystallises from petroleum ether in salmon-red plates, 

 m.p. 182°. It is vitamin A-inactive even in high doses. 



Solvent: Absorption maxima 



Carbon disulphide 461 432 m/j, 



(cf. Fig. 30, p. 360 and Fig. 31, p. 361) 



Perhydrocarotene C40H78 : 



Perhydrocarotene is obtained by the hydrogenation of jS-carotene in the 

 presence of colloidal platinum as catalyst^ "''. Perhydrocarotene is a very 

 viscous, distillable oil. It is very soluble in cyclohexane, easily soluble in ben- 

 References p. 165-ijo. 



