202 THE CARBOHYDRATES. 



CH 3 



zol, C NHk , from glucose by the action of ammonium-zinc hydroxide 

 II >CH 



CH N^ 



at ordinary temperatures. This formation can be conceived as follows: 

 First methyl glyoxal is formed from the sugar, and then from this, or 

 from the sugar, formaldehyde is produced, which reacts with the methyl 

 glyoxal with the formation of methylimidazole according to the following 

 equation : 



CH 3 CO NH 3 H x H 3 C.C NH X 



| ' + + >CH= || >CH+3H 2 O 



COH NH 3 W CH N^ 



Methylglyoxal Formaldehyde Methylimidazole 



A genetic relationship of the carbohydrates to histidine and the purine 

 bodies is thus made probable by the imidazole formation. 



As the sugars are derivatives of polyhydric alcohols, they also form 

 esters, among which the benzoyl ester is of special interest because it is 

 used in the detection and isolation of the sugars and also of other car- 

 bohydrates. The nucleic acids probably also belong to the acid esters 

 of the sugars, and thus may be considered as complex phosphoric acid 

 esters, and perhaps the chondroitin sulphuric acid and the glucothionic 

 acid are sulphuric acid esters. The nature of these two groups of 

 sulphuric acid esters is not yet thoroughly understood. 



The sugars can also combine with other bodies and with each other, 

 forming ether-like combinations. By the action of hydrochloric acid 

 as catalyst, as shown by FISCHER and collaborators, the sugars split off 

 water and unite with other bodies, producing lactone-like combinations, 

 which have bein called glucosides (see pages 61 and 200). These glucosides, 

 which are generally compounds with aromatic groups, occur widely dis- 

 tributed in the vegetable kingdom. The more complex carbohydrates 

 may be considered, according to FISCHER, as glucosides of the sugars. 

 Thus maltose, for example, is the glucOside and lactose the galactoside 

 of glucose. The glucosides can be split into their components by chem- 

 ical agents, boiling with dilute mineral acids, as well as by the action 

 of enzymes. The complex sugars hereby yield simple sugars and the other 

 glucosides yield compounds which belong either to the aromatic or the 

 aliphatic series besides the sugar. A long-known example of a decom- 

 position of this kind is the splitting of amygdalin by the enzyme emulsin 

 (see page 60). 



With phenylhydrazine or substituted phenylhydrazines, the sugars 

 first yield -hydrazones with the elimination of water, and then on the fur- 

 ther action of hydrazine on warming in an acetic-acid solution we obtain 

 osazones. 



