THE CHEMISTRY OF THE SUGARS 87 



nature and which have a practical as well as a scientific import- 

 ance, and it is unnecessary, therefore, to extend it further. 



All these aldoses and ketoses have certain general reactions 

 by which they can be readily identified :— 



1. They are readily reduced by nasoent hydrogen to the 

 corresponding alcohols, the aldehyde and ketone group being 

 attacked, thus : — 



CH^OH CH^OH CH2OH CH^OH 



(CHOH)4+H2 = (CHOH), (CHOH), (CH0H)3 



I I 1 +H, = I 



CHO CHgOH CO CHOH 



] I 



CH3OH CHjOH 



2. Dilute nitric acid oxidises aldoses to oxycarboxyhc acids, 

 thus : — 



CH20H(CHOH)4CHO + = CH20H(CH0H)4C02H 



With ketoses the chain is broken on oxidation : — 



CH20H(CHOH)3COCH20H + 30 = 



C02H{CHOH)2C02H + COaHCH^OH 



Tartaric acid Glycolllo add 



3. Phenyl-hydrazine converts both aldoses and ketoses into 

 hydrazones and finally into osazones by the following impor- 

 tant reactions : — 



Aldose — 



i. -CHOHCH^O+Hj^NNHCeHs 



Aldose group Phenyl-hydrazine 



— -CHOHCH=N-NHC8H5 -f H^O 



Hydrazone 



ii. -CH0HCH=N-NHCeH5 + CeHsNHNH^ 



^ -COCH=N-NHC8H5 + CeH^NHj-l- NH, 



O^bonyl compound 



