HEX08ES 



65:^ 



(a) and (b) will be in dynamic equilibrium with the enol (c). Now if II and 

 OH are again taken on by (a) and (b) this assumption of the elements of water 

 can take place in thrt-c different ways, to regenerate d Icvulose, d-nianiiose and 

 4-glucose. Thus if in the case of (a), Oil is added to carbon atom number one 



OH 



I 

 tins will form tlie group H — C — OH whicli represents a hvdrated aldeiivde "roup 



I . . » 1 



and will lose water to become CHO. 'ihen H going to the second C atom 

 completes the formula of d-mannose. In a similar way (b) can form d-glucose. 

 But if tlie OH went to the second carbon atom this group would tliereby 

 bi'come a hydrated ketone similar to the hydrate of acetone and lose water 



to form = 0, while H going to the end carbon atom woukl coiiiplete tiie formula 



of d-Icvulose. In a manner entirely analogous there is an enol molecule which is 

 common to d-allose, d-latose and d-pseudo fructose (see (d) above). 



It will be noticed that each of these enols is in equilibrium witli a 2-keto- 

 hexose and two aldo-hexoses. Now these 2-keto-hexoses, d-fructose and d-pseudo 

 fructose, in accordance with general ketone behavior, are capable of yielding an- 

 other common enol, /. e., a 2-3 enol (with the double bond between tlie second and 

 third carbon atoms) as represented at (e) and this 2-3 enol (by a process like 

 that just detailed for the 1-2 enols) can' accoimt for the formation of the two 

 3-keto-hexoses whose formulae are given above. The same general principles hold 

 for each of the series of hexoses ( For further elaboration of the theory 

 see Nef's original papers.) A similar use of enol molecules in this connection 

 is made In' Neuberg. 



It remains now to point out that if to a simple aqueous solution of sugar, 

 oxygen be supplied in the form of air or HoO^, no oxidation occurs. But if the 

 solution be alkalinized then the sugar is readily burned. In the absence of 

 oxygen and the presence of alkali somewhat stronger than that foimd most 

 favorable for the reciprocal transformation above detailed, there occur certain 

 irreversible reactions such as the formation of lactic acid and the so-called 

 saccharines. When an alkaline sugar solution is treated with oxygen it yields 

 COo, H„0, and formic, glycollic, glyceric and certain trihydroxy-butyric and 

 hexonic acids, depending on the sugar used. Witliout oxygen, or witii too little 

 oxygen, lactic acid and the saccharinic acids make their appearance (cf. the forma- 

 tion of lactic acid). The explanation of these phenomena rests in tlie conception 

 that alkali increases the dissociation of sugar, and tliat tlie dissociated fragments 

 burn or rearrange depending upon tlie conditions of the experiment. 



In this connection, according to Nef, we are dealing with the alcohol groups 

 of the sugars and may advantageously turn for a moment to the properties of 

 inethvl alcohol. This substance consists imder ordinarv circumstances of a great 



Glucose 

 (1) 



O 



II 

 C— H 



I 

 H— C— OH 



I 

 OH— C— IT 



I 

 H— C— OH 



I 

 H— C— OH 



H— C— OH 



H 



Glucose ion 



(2) 



(— ) 







II 



C— H 



I 

 H— C— 0— 



I 

 OH— C— H 



I 

 H— C— OH 



H— C— OH 



I 

 II— C— OH 



I 

 H 



( + ) 

 — H 



K-glucosate 

 (3) 



O 



II 

 C— H 



I 

 H— r— OK 



I 



OH— C— IT 

 I 

 H— C— OH 



I 

 H— C— OH 



I 



H— C— OH 



I 

 H 



Metliylene 

 particle. 

 (4) 



O 



II 

 C— H 



I 

 — C— 



I 

 no— C— II + KOH 



r 



H— C— OH 



I 

 H— C— OH 



II— C— OH 



I 

 H 



