122 CAROTENOID HYDROCARBONS OF KNOWN CONSTITUTION X 

 CH, CH, CH, CH3 



C CH3 CH3 CH3 CH3 C 



CH CH-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CHCH CH 



CH C-CH3 H3C-C CH 



\v / Dedydrolycopene \ ^ 



\h CH 



Dehydrolycopene contains 15 conjugated double bonds. It can only be 

 crystallised from pyridine, being almost insoluble in most other solvents. The 

 crystals appear dark violet to black in direct light and are slowly discoloured 

 and decomposed on heating in an evacuated tube above 200°, no definite 

 melting point being observed. With a solution of antimony trichloride in 

 chloroform, dehydrolycopene gives a fairly stable blue colouration, the ab- 

 sorption spectrum of which exhibits a sharp band with a maximum at 472 m/i 

 and continuous absorption above 640 m//. 



Solvent: Absorption maxima: 



Carbon disulphide 601 557 520 mn 



Hexane 542 504 476 m// 



Benzene 570 531 493 mfx 



Pyridine 574 535 498 m^ 



Chloroform 567 528 493 m/z 



Apo-2-lycopenal (lycopenal*) C3,H420: 



OHC-CH=CH-C=CHCH=CH-C=CHCH=CHCH = C-CH=CHCH=C-CH=CHCH=C-CH2CH2CH=C-CH, 



II I I I I 



CH3 CH3 CH3 CH3 CH3 CH3 



Lycopenal is obtained by the chromic acid oxidation (3 atoms O) of lyco- 

 pene in a mixture of acetic acid and benzene*-. It crystalUses from a mixture of 

 benzene and ethanol in deep-red plates, melting point 147° (corr.). It is easily 

 soluble in chloroform, carbon disulphide and benzene, but only sparingly in 

 ethanol. It is entirely epiphasic in the partition test. 



Solvent: Absorption maxima: 



,. ' .. Carbon disulphide 569 528.5 493.5 m/t 



Petrol 525.5 490.5 455.5 m^ 



Lycopenal is very easily oxidised in the solid state or in solution. On treat- 

 ment with chromic acid (3 atoms O), 2-methylhept-2-en-6-one and apo-2:i2- 

 lycopene dialdehyde (bixin dialdehyde)*^ are formed. With free hydroxylamine, 

 apo-2-lycopenal gives apo-2-lycopenal oxime wich crystallises from pyridine 

 in lustrous blue- violet prisms, 198° (corr., evacuated capillary). 



The old name for apo-2-lycopenal is lycopenal. 

 References p. 165-iyo. 



