462 



CHLOROPHYLL 



CHAP. 16 



Table 16.11 



Oxygen Absorption by Chlorophyll Derivatives 

 (Fischer and Riedmeier, 1933) 



(A) Substitution Effect in Ethanol. 



If the absorption of oxj^gen is localized in position 10, as assumed by 

 Fischer, the necessity of magnesium for this reaction is another illustration 

 of the influence of magnesium on the properties of the cyclopentanone 

 ring, mentioned several times above. 



While it seems definite that allomerization consists of an oxidation 

 of the CH — group in position 10, it is less certain whether the allomer- 

 ized product is a "chlorophyll peroxide" or an "hydroxjxhlorophjdl." 

 The chemical structure and spectrum of allomerized chlorophyll certainly 

 deserve closer study, since it is the simplest oxidation product of chloro- 

 phyll. It would also be important to know whether this oxidation can 

 be conducted in a reversible way; so far, allomerization has usuall}^ been 

 treated as an irreversible change (although StoU and Wiedemann, 1932, 

 asserted that the allomerization of compounds of the 6-series can be 

 reversed by mild reductants). 



Allomerization can be delayed or prevented by small quantities of 

 acid (Willstatter and Stoll) or b}' the presence of reducing substances 

 (StoU and Wiedemann). Allomerized chlorophyll still reacts with cold 

 alkaU under the conditions of the phase test, but gives green chlorins 

 directlj^ without the intermediate formation of a "brown phase." In 

 preparation for a later discussion (pages 465 and 493), it may be useful 



