44 



CHEMISTRY OF PLANT LIFE 



having carried the process as far as the production of glucodecose 

 (CioH 2 oOio). It usually happens, however, that two stereo- 

 isomers result from the " step-up " by way of the nitrile reaction; 

 thus, arabinose yields a mixture of glucose and mannose, glucose 

 yeilds glucoheptose and mannoheptose, etc. 



The reverse process, or the so-called " degradation " of a sugar 

 into another containing fewer carbon atoms, may be readily 

 accomplished in either one of two ways. In Wohl's process, the 

 aldehyde group of the sugar is first converted into an oxime, by 

 treatment with ammonia; the oxime, on being heated with con- 

 centrated sodium hydroxide solution, splits off water and becomes 

 the corresponding nitrile; this, on further heating, splits off HCN 

 and yields an aldose having one less carbon atom than the original 

 sugar. This process is the exact reverse of the nitrile synthesis, 

 described above. The second method of degradation, suggested 

 by Ruff, makes use of Fenton's method of oxidizing aldehyde 

 sugars to the corresponding monobasic acid, using hydrogen 

 peroxide and ferrous sulfate as the oxidizing mixture; the aldonic 

 acid thus formed is then converted into its calcium salt, which, 

 when further oxidized, splits off its carboxyl group and one of the 

 hydrogens of the adjacent alcoholic group, leaving an aldose having 

 one less carbon atom than the original aldose sugar. 



Enolic Forms. A final avenue for the interconversion of glu- 

 cose, mannose, and fructose into one another, is through the 

 spontaneous transformations which these undergo when dissolved 

 in water containing sodium hydroxide or potassium hydroxide. 

 This change is due to the conversion of the sugar, in the alkaline 

 solution, into an enol } which is identical for all three sugars, and 

 which may subsequently be reconverted into any one of the three 

 isomeric hexoses. The relationships involved are illustrated in 

 the following formulas: 



CHO CHO CH 2 OH CHOH 



C 



H C OH HO C H 



i 



=O 



C-OH 



HO C H 

 H C OH 

 H C OH 

 CH 2 OH 



Glucose 



HO C H HO C H 

 H C OH H C OH 



H C OH 



?H 2 OH 



Mannose 



H C OH 

 CH 2 OH 



Fructose 



H C OH 

 CH 2 OH 



Enolic Form 



