520 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Chlorophyll a differs from chlorophyll b in containing a lactam group, 

 which is suggested as existing between the third COOH group and an NH 2 

 group, termed the y group. Chlorophyll b does not apparently contain a 

 lactam group. They are represented by the furmulae : 



M g C 31 H 29 N 3 - COOCH 3 . MgC 32 H 28 2 N 4 COO CH 8 



-co y 



NH y 



Chlorophyll a Chlorophyll b. 



Both chlorophyll a and chlorophyll b are very unstable compounds, being 

 decomposed by acid, alkali and the enzyme chlorophyllase, which is present in 

 the plant together with the chlorophylls. 



Action of Chlorophyllase. Crystalline Chlorophyll. 



Chlorophyllase acts upon chlorophyll a and chlorophyll b in methyl or 

 ethyl alcoholic solution. The action takes place during a slow extraction of 

 the chlorophyll from the leaf with dilute alcohol. The effect of the enzyme 

 is to hydrolyse the ester partially ; it removes the phytol and at the same 

 time the COOH group is esterified with the methyl or ethyl alcohol. In the 

 case of methyl alcohol the change is 



chlorophyll a > methyl chlorophyllide a chlorophyllide a 

 (methyl phytyl chlorophyllide a) (methyl-methyl chlorophyllide a) (methyl chlorophyllide a) 



chlorophyll b > methyl chlorophyllide b > chlorophyllide b 

 (methyl phytyl chlorophyllide b) (methyl-methyl chlorophyliide b) (methyl chlorophyllide b) 



These compounds crystallise very readily on evaporation of the solution. 

 Crystallised chlorophyll is a mixture of ethylchlorophyllide a and ethylchloro- 

 phyllide b. 



Action of Alkali. Decomposition of the Chlorophylls. 



By the action of alkali upon chlorophyll the ester groupings are hydrolysed. 

 At the same time a rearrangement occurs in the molecule of both chlorophyll 

 a and chlorophyll b. Two products are obtained from each, namely, the tribasic 

 acids, chlorophyllin a and isochlorophyllin a, chlorophyllin b and isochloro- 

 phyllin b. 



In the case of chlorophyll a the action of alkali is also to open the lactam 

 ring and the formation of another lactam ring with either the a COOH group 

 and the y NH 2 group or the y COOH group and the 8 NH 2 group. 



The chlorophyllins on heating with alkali lose carbon dioxide yielding 

 dibasic acids. On heating these dibasic acids to a higher temperature carbon 

 dioxide is again split off and monobasic acids are formed. If these mono- 

 carboxylic acids be heated with soda lime, they lose carbon dioxide and yield 

 the corresponding hydrocarbon, aetiophyllin. These changes are represented 

 as follows : 



