18 



IMMUNO-CATALYSIS 



the base-catalyzed reaction the hydrogen of the hydroxy! group 

 attached to the carbon (*) Hnked to the ether-oxygen is first reversibly 

 removed by the catalyst base. Then an acid reacts at a much slower 

 rate with the anion formed to produce the symmetrical form. 



+ HA 



H Ol 



HO— C lOI 



HO— C C— CH2OH 



H OH 



H 01 



\' 



«x/ - 

 HO— C 10— H + A 



"xl I 



HO— C C-CH2OH 



\/^H 



H^%H 



As can be seen, both an acid and a base are needed to catalyze the 

 mutarotation. In this reaction there is an addition as well as the removal 

 of a hydrogen ion. In either case, the conversion of the carbonyl form 

 of glucose to the ring form may take place in either configuration of 

 the carbonyl carbon, and this is responsible for the change to an 

 equilibrium mixture of a- and /3-glucose, with a change of rotation to 

 that of the mixture (Hammett, 1940, p. 337). 



b. Acid Catalyzed Enolization. Enolization in Concentrated 

 Aqueous Acid. As an example of enolization in concentrated aqueous 

 acids again the primary reactions involve the formation of the conjugate 

 acid of the ketone which in turn loses its H+ to a molecule of water as 

 a base. Hammett (1940, p. 276), believes that in strong acid this 

 molecule of water forms part of the complex in the transition state of 

 the enolization of acetophenone. 



