6 CAPSANTHIN 243 



spectral properties: 



Solvent Absorption maxima 



Carbon disulphide 542 503 m^ 



Petrol 505 475 m^ 



Benzene 520 486 m// 



(cf. Fig. 14, p. 353) 



Solutions of the pigment in ethanol are deep red. Solutions in petrol are 

 lemon to orange-yellow. 



Colour reactions: On treating a solution of the pigment in chloroform with 

 concentrated sulphuric acid, the latter assumes a deep blue colouration. On 

 treating an ethereal solution of the pigment with concentrated aqueous hydro- 

 chloric acid, no colour change is observed. Capsanthin gives a deep blue 

 colouration with antimony trichloride in chloroform. Numerous other colour 

 reactions have been described by Zechmeister^*. 



Optical activity: [aj^a = +36° (in chloroform). 



Partition test: On partition between petroleum ether and 90% methanol, 

 capsanthin is found quantitatively in the lower layer. 



Chromatographic behaviour: Capsanthin is well adsorbed on calcium carbo- 

 nate or zinc carbonate from carbon disulphide or from a mixture of benzene; 

 and ether (1:1). It is found above violaxanthin on the chromatogram column. 

 Elution is effected by means of methyl or ethyl alcohol or by means of an_ 

 ether-methanol mixture (5:1)*. 



Detection and estimation: For a micro-method for the identification of 

 capsanthin, compare Zechmeister^*. The simplest method of identifying the 

 pigment is the determination of the absorption spectrum. According to Zech- 

 MEiSTER^* the following reaction is characteristic of the pigment. A layer of 

 30% methanolic potassium hydroxide is formed under a solution of capsanthin 

 in petroleum ether, and the mixture is allowed to stand undisturbed for one 

 day. At the end of this period, deep red needles are formed. 



Physiological properties: According to B. v. Euler, H. v. Euler and 

 Karrer^^ capsanthin has no vitamin A activity. 



Chemical behaviour: Capsanthin is not acidic in character but there are cer- 

 tain indications that the pigment is at least partly enolised. Thus, when the 

 pigment is chromatographed on calcium carbonate from benzene, two zones 

 are regularly observed^®. The same behaviour was observed by Karrer and 



Concerning the observation of L. Zechmeister and L. v. Cholnoky that the pigment 

 forms two zones in the chromatogram on calcium carbonate, cf. the section on cis-irans- 

 isomerism, p. 248. 



References p. 253-25$. 



