106 CHEMISTRY OF PLANT LIFE 



/COO C 2 oH 3 9 /COO C 2 oH 39 



MgC 3 iH 29 N 3 ^-COO - CH 3 MgC 32 H 28 2 N4- C00 ' CH 3 



NH-CO Chlorophyll 6 



Chlorophyll a 



The chlorophylls are unstable compounds, readily acted upon 

 by acids or alkalies, and by the enzyme chlorophyllase, which 

 splits off the phytyl alcohol group. The progressive action of 

 acids and of alkalies in breaking down the molecule, and the prod- 

 ucts of its oxidation and reduction, have served to establish the 

 chemical composition of the compound in each case. Because 

 of the importance of these pigments in the whole metabolic proc- 

 esses of the plant, it seems to be desirable to consider the nature 

 of these reactions in some detail, as follows : 



Decomposition of the Chlorophylls by Alkalies. The first 

 action of dilute alkalies on the chlorophylls is to split off, by 

 hydrolysis, the alcoholic groups of the esters, producing the crys- 

 talline tri-basic acids, or chlorophyllins a and b. Each of these 

 chlorophyllins exists in two forms, the normal and the iso, in which 

 the attachment of the COOH groups to the other groups in the 

 molecule is in different positions. Hence, chlorophyll a yields 

 chlorophyllin a and isochlorophyllin a, and chlorophyll b yields 

 chlorophyllin b and isochlorophyllin b, all four of which are tri- 

 basic acids. 



These compounds, when heated with alkalies, split off carbon 

 dioxide in successive stages, losing one COOH group at each step, 

 thus yielding a series of simpler compounds of the following types: 

 First, di-basic acids; second, monobasic acids; and finally, 

 cetiophyllin, a compound in which no COOH group is present. 

 In all of these compounds, derived from chlorophylls by the action 

 of alkalies, the Mg remains in the molecule, and all the Mg-con- 

 taining derivatives from the chlorophylls are known as " phyllins." 

 At the stage at which only one COOH group remains in the 

 molecule, only one group arrangement is possible, and the 

 derivatives from chlorophyllin a and isochlorophyllin 6, and those 

 from chlorophyllin b and isochlorophyllin a, are identical. At 

 the final stage, the derivatives from all four forms are identical. 

 This may be graphically illustrated by the following diagram indi- 

 cating the progressive decomposition of the two chlorophylls 

 under the action of alkalies: 



