24 TORULARHODIN 331 



weaker than that of j3-carotene. Since growth-promoting properties are generally- 

 associated with the presence of an unsubstituted jS-ionone ring, it appears 

 probable that such a ring is present in torularhodin. On the basis of these facts, 

 the following possible structural formula, which is in agreement with the 

 analytical data, the number of double bonds and the absorption spectrum, 

 can be deduced. 



C CH3 • CI13 CH3 CH3 



/\ I I II 



CH2 C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-CH COOH 



CH2 C"CH3 H3C'C CH 



\/ Torularhodin( ?) \ Z' 



CH2 CH 



In accordance with its acidic nature, torularhodin forms salts with alkalis. 

 The salts exhibit the same optical properties as the free pigments, showing that 

 salt formation does not result in any structural changes. The pigment is entirely 

 indifferent to hydro xylamine in boiling ethanol and towards boiling alcoholic 

 potassium hydroxide. Torularhodin is reduced by zinc dust and acetic acid 

 in pyridine. This reaction is of considerable interest, as it has previously only 

 been observed with carotenoids containing systems of conjugated double bonds 

 terminated by two carbonyl or carboxyl groups (e.g. bixin, crocetin, rhodo- 

 xanthin, j3-carotenone etc.). Torularhodin is rapidly reduced under the same 

 conditions to give a light yellow product exhibiting the following absorption 

 maxima. 



Solvent: Absorption maxima: 



Carbon disulphide 482 453 m^ 



Petroleum ether 453 m/j, 



This compound shows an acidic reaction and is more hypophasic than 

 torularhodin on partition between methanol and petroleum ether. The displace- 

 ment of the absorption bands towards the violet relative to the parent pigment 

 is extraordinarily large for a dihydroderivative. 



Properties 



Crystalline form: Torularhodin crystallises in fine red needles on slowly 

 evaporating a methanol-ether solution. From a mixture of benzene and 

 methanol, the compound is obtained as a violet-black crystalline powder. 



Melting point: 201-203° (with decomposition, uncorr., in vacuum) 



References p. 341-343. 



