3 ^-CAROTENE 131 



carotene is precipitated with ethanol. Spirits of wine are added in small portions 

 every 2 to 5 minutes. At first only colourless materials separate. As soon as the first 

 carotene crystals are formed, the colourless materials are separated by rapid 

 filtration. The mother liquors are diluted with the remainder of the alcohol (about 

 3_6 volumes of the original carotene solution are required) and allowed to stand 

 for 20 hours at -10°. After this time the crude carotene is filtered off, dissolved in 

 carbon disulphide, precipitated with ethanol, extracted with a little warm petroleum 

 ether to remove remaining impurities, and finally recrystallised from a large volume 

 of petroleum ether. 



In order to obtain the pure /3-isomer from crude carotene, the latter is chromato- 

 graphed from petroleum ether on calcium hydroxide'^ Karrer and Walker'^ 

 obtained 17 g of pure /S-carotene and 2.5 g of pure a-carotene from 35 g of crude 

 carotene. 



In contrast to Willstatter and Escher'^, Kuhn and Lederer'* submit the 

 shredded carrots to a preliminary extraction with methanol. 



Chemical Constitution 

 CH, CH, CH, CH, 



C CH, CH, CH3 CH3 C 



/\ I I I I /\ 



CH2 C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CHj 



CH2 C-CH3 HsC-C CH2 



\^ / /5-Carotene ' \ / 



CHa CH2 



In 1907, Willstatter and Mieg" established the correct molecular formula 

 C40H56 for carotene. Zechmeister, von Cholnoky and Vrabely'^^ showed that 

 carotene contains 11 double bonds which can be saturated by hydrogenation. 

 The formula of perhydrocarotene, C40H78 proves the presence of 2 ring systems. 

 According to Pummerer and Rebmann'^^ carotene absorbs 11 molecules of 

 iodine chloride, thus confirming the presence of 11 carbon-carbon double bonds. 



Karrer and co-workers'* oxidised jS-carotene with permanganate and with 

 ozone and obtained a:a-dimethylglutaric acid, a:a-dimethylsuccinic acid, 

 dimethylmalonic acid and geronic acid (a :a-dimethyl-6-acetylvaleric acid), 

 the latter being a particularly characteristic degradation product. All these 

 compounds are also formed by the oxidation of /5-ionone, in comparable yield. 

 Thus by the oxidation of pure /^-carotene, Karrer and More obtained geronic 

 acid in 16 % yield, while ^-ionone afforded the acid in 19.4 % yield. It was 

 thus concluded that jS-carotene contains two j8-ionone groupings. 



CH, CH, 



C 



/\ 

 CHg C 



I II 



\V 



CH2 



|3-ionone group 

 References p. 165-iyo. 



