104 CHEMISTRY OF PLANT LIFE 



transient pure yellow color. Chlorophyll b is dark green, is some- 

 what less soluble than the other form, and when saponified by 

 potash gives a transient brilliant red. 



Amorphous and Crystalline Chlorophyll. When the chloro- 

 phyll of plants is extracted by alcohol and the alcoholic extract 

 evaporated nearly to dryness, beautiful dark green crystals are 

 obtained. Willstatter has shown, however, that in these crys- 

 tallized forms the ethyl group (from the ethyl alcohol used) has 

 replaced the phytyl group (see below) which is present in the pig- 

 ments as they exist in the plant tissues; and that, when 

 extracted by other solvents than alcohol, the pigments may 

 be obtained in the amorphous forms in which they exist in 

 the plant. 



This change from amorphous to crystalline compounds may be 

 understood from the preliminary statement that the chlorophylls 

 are esters of tri-basic acids, in which one acid hydrogen is replaced 

 by the methyl (CHs) group and a second by the phytyl (C2oHs9, 

 from phytol, or phytyl alcohol, C2oHs9OH) group. When treated 

 with ethyl alcohol (C2HsOH) for the purpose of extracting the 

 pigments, the ethyl (C2Hs) group replaces the phytyl group, thus 

 yielding a methyl-ethyl ester, and these esters are the crystalline 

 forms of the chlorophylls. This replacement is made possible 

 through the action on the original pigment in the tissues of an 

 enzyme, chlorophyllase, which is also present in the tissues, which 

 splits off the phytyl group, forming phytyl alcohol, and leaving a 

 free COOH group in the pigment, with which the alcohol used 

 in the extraction forms the ethyl ester (see Chapter IX for a dis- 

 cussion of the formation and hydrolysis of esters). 



While the chlorophylls are tri-basic acids, only two of the 

 acid COOH groups actually function in ester-formation. The 

 third acid group seems not to exist as a free acid group; but in 

 chlorophyll a, it is in what is known as the " lactam " arrangement, 

 represented by the CONH group, and in chlorophyll 6, it is 

 probably in the " lactone " arrangement, represented by the 

 COO group; the two bonds in each case being attached to 

 different structural units in the molecule (see page 106). 



The change from amorphous to crystalline forms may be repre- 

 sented by the following formulas, in which the R represents the 

 whole of the complex group to which the acid ester groups are 

 united: 



