652 DIABETES 



H H 



CH3— c = + n on ^ ciia— c— OH 



ok 



This hydrate possesses ioiiizable hydrogen in its OH groups, and in the presence 

 of a metallic liydroxide, MOH, can accordingly form a salt (comparable to an 



H 



alcoholate) ; tiius: CHj — C— OH, 



and this salt being highly dissociable falls apart into MOH and a "methylene 

 enoV (in this case hj'droxyethylidene) : 



H 



1 * I 



CH3— C— OH ^ CH3— C— OH + MOH. 



I 1 



OM 



(Herein lies the point of departure of Nef's view from the foregoing.) This 

 methylene enol then rearranges to form the "olefine dienol" CHo = CHOH (in this 

 case vinyl alcohol). Ketones, on the other hand, form the oletine dienol directly 

 without forming the methylene enol. In the case of KOH and acetone (dimethyl 

 ketone) there is the same formation of the hydrate followed by salt formation and 

 the loss of KOH, but the latter does not all come from one C atom as it does 

 when split out of aldehydes, thus: 



OH OK 



1 I II 



CH3— C— CH3 + KOH ^ CH3— C— CH3 + ILO <^ GH3— C— CH2 



OH OH OH 



( hydrate of acetone ) 



In a manner entirely analogous to what occurs in the simple aldehydes and 

 ketones, the two aldohexoses, glucose and mannose, and the ketohaxose levuloso, 

 can form one and tlie same enol molecule. And vice versa this enol molecnli may 

 open its double bond in two ways as shoAvn below ( (a), (b) and (c) ) and the 

 dissociated molecules. 



