OCf'TTRRENCE AND STRTTCTTTRE OF RELATED rOMPOTTNDS 



-03 



nol, 1400; chloroform, 1303. Curves for these absorption spectra are in- 

 cluded in Figure 2. 



When crj^stalline vitamin Ai aldehyde reacts with antimony trichloride, it 

 is found that the absorption maximum is at 664 mix, and the E (1%, 

 1 cm.) value amounts to 3400. A number of derivatives were prepared, 

 including the 2:4-dinitrophenylhydrazonc (reddish brown needles, m.p., 

 207-208°C.) and the semicarbazone, m.p., 161-164°C., X(ciici3) = 385 mM, 

 E (1%, 1 cm.) = 1748. Two hydrazones were obtained, one melting at 



2000 





1000 



500 



250 



300 350 400 



WAVE LENGTH IN MXL 



Fig. 2. Absorption spectra of vitamin A aldehyde in various solvents: 



(-•-•-) light petroleum ether; ( ) fyelohexane; (- -) ethanol; ( — ) 



chloroform. *i 



108-109°C. and the second at 135-145°C. However, with pure retinenei, 

 the semicarbazone had a melting point of 193-195°C. and E (1%, 1 cm., 

 385 m.\x) = 2062. The hydrazone obtained from the pure retinene melted 

 at 177°C. and had two maxima, E (1%, 1 cm., 462 m/x) = 1930 and E 

 (1%, 1 cm., 297 m/x) = 334. 



As noted earlier, vitamin A2 aldehyde has been shown to be the same as 

 retinenco. The retinal pigment was first obtained in crystalline form by 

 Salah and Morton. ^^^ Wald,'" who prepared it first from the retinas of 

 frogs, '^^ characterized it as a deepl}^ yellow substance soluble in petroleum 

 ether. '^' According to Morton, Salah, and Stubbs'^^ it has a maximum ab- 

 sorption at 405 m/x in chloroform, and reacts with antimony chloride to 

 give a color with a maximum at 702-706 mju. It has also been prepared 



1" G. Wald, 'Salure, IS4, 60 (1934). 



