OF THE CARBOHYDRATES 65 



By appropriate methods it is possible to convert sugars into others 

 containing more carbon atoms and vice versa. Thus the aldoses 

 combine directly, with Hydrocyanic Acid with the formation of Nitriles, 

 in accordance with the equation: 



C 5 Hn0 5 .CHO + HCN = C 6 HuO 6 CH(OH).CN 



These nitriles^on hydrolysis, yield acids containing one carbon atom 



more than the original carbohydrates, thus: 



C5HnO 5 .CH(OH).CN + 2H 2 O = C 5 H U O 5 CH(OH)COOH + NH 3 



Reduction of these acids, by means of sodium amalgam, yields the 

 corresponding aldose with one carbon atom more than the original 

 sugar. In this way glucose has been prepared from arabinose, and 

 seven- and even nine-atom sugars have also been prepared, by successive 

 steps, starting with glucose. 



The conversion of a sugar containing more, into one containing fewer 

 carbon atoms may be accomplished by converting the sugar by gentle 

 oxidation into the corresponding (monobasic) acid, and then subjecting 

 the calcium salt of this acid to further oxidation, with the result that 

 the carboxyl-group is decomposed into carbon dioxide and water, and 

 a sugar containing one less carbon atom than the original sugar is 

 formed : 



CHO COOH 



I i 



CH(OH) CH(OH) A COH 



I I if I 



CH(OH) CH(OH) CH(OH) 



I I t/l 



CH(OH) CH(OH) - CH(OH) + CO 2 + H 2 O 



I I .1 



CH(OH) CH(OH) CH(OH) 



i I ! 



CH 2 (OH) CH 2 (OH) CH 2 (OH) 



Aldo-hexose Aldonic acid Aldo-pentose 



This reaction is of very great interest to the biochemist because the 

 conversion of a carboxyl- group into CO 2 and H 2 is known to be readily 

 accomplished by bacterial action and probably also by animal tissues. 

 TJie possibility is thus indicated that pentoses in the tissues may be 

 derivable from glucose, a possibility, the significance of which will be 

 apparent at a later stage. 



Not only is it possible to convert a hexose into a pentose and vice 

 versa, but it is also possible to convert one hexose into another. It was 

 found by Lobry de Bruyn that in the presence of alkalies, glucose, 

 mannose or levulose in aqueous solution yields a mixture of the three 

 sugars. More concentrated alkali brings about more pronounced 

 decomposition, as is evidenced by the formation of lactic acid and other 

 hydroxy-acids in Moore's test for carbohydrates. The production of 

 lactic acid from glucose by the action of alkalies is a phenomenon of 

 5 



