42 A. S. HOLT 



whether in the crystalline state or in polar or nonpolar solvents, gives 

 no evidence, in its infrared absorption spectra, of the formation of an 

 enol. From methanolic solutions exposed to air, several products of 

 allomerization of chlorophyll a were separated chromatographically. 

 Comparison of visible absorption spectra, acid numbers, and other 

 properties of these products and their pheophorbides with those of 

 compounds characterized earlier by Fischer (7) shows them to be 

 phyllins of (/) purpurin-7-triester, {2) purpurin-7-lactone ether, (5) 

 10-o\y-pheophorbide a, and (4) purpurin 18. The infrared spectra 

 of the phyllins of {2) and {4) in CCI4 are difficult to reconcile with the 

 known chemical structural formulas, and are markedly changed 

 upon removal of magnesium. The phyllins of {1) and (5) readily 

 form the "Krasnovskii reaction" intermediate; all four products are 

 bleached by FeCla in methanol solution. 



Discussion 



Linschitz: A study of the allomerization reaction has recently been made in 

 our laboratory by Mr. Sol Oilman, who has obtained data on the nature of the 

 different allomerization products which nicely supplement Dr. Holt's very 

 thorough infrared study. In particular, the results indicate, in agreement with 

 Dr. Holt's proposals (and earlier work as well) that his Fraction-2 is a chlorophyll 

 oxidation product with a lactone structure in ring-5 (A), while Fraction-3 is a simi- 

 lar product but ivilhout the lactone oxygen (B). 



/ // 



N— C N— C 



% // \ V -^ V 



C— C /C C— C .0 



EtO-C 

 (HO)/V / 



10 



/ 



, 0— C EtO-C— C 



COOMe V (HO) I Wq 



COOMe 



A ("Fraction = 2" Holt) B ("Fraction = 3!' Holt) 



(a = ethoxy, a = hydroxy) (/3 = ethoxy, /3' = hydroxy) 



In Oilman's work, methods were developed for preparing each of these four 

 derivatives separately in good purity and yield. For example a' can be made by 

 exposing the enolate of chlorophyll to air, in pyridine solution, /3' by allomerizing 

 chlorophyll in alcohol with ammonium acetate, and /3 by the oxidation of chloro- 

 phyll with quinone, in air-free alcohol. The structures were established by con- 

 verting to previously known compounds, by chemical analysis, and by spectral 

 and chromatographic data. The derivatives a, a', and 0' constitute about 90% 

 of the various products obtained when chlorophyll is allomerized in the usual way, 



