ANTIGENS AS BIOCATALYSTS 21 



However, in the case of unsymmetrical reactants different reaction 

 products are obtained by acid and base catalysis shown below (Ham- 

 mett and Getder, 1943). 



H H 



CeHa— C = + CH3— C— CH2CH3 ^^^^ CeHs— C = CH— C— CH2CH3 



II II 



o o 



Benzaldehyde Methyl ethyl ketone Ethyl styryl ketone 



No solvent, 

 reagents saturated 

 with HCl gas 



CH3C — C — CH3 



II II 

 O CH 

 I 

 CeHs 



Methyl ^-methyl styryl ketone 



f. Hydrolysis of Esters. Carboxyliq ester hydrolysis reactions are 

 slow reversible reactions catalyzed by both hydroxyl and hydrogen 

 ions. The alkaline hydrolysis of an ester is a reaction between the ester 

 molecules and hydroxyl ions, while in the acid catalyzed reaction a 

 molecule of water may form a part of the transition state complex. 



Base Catalyzed Hydrolysis. In this hydrolysis the carbon-oxygen bond 

 that breaks is between the carbonyl carbon and oxygen and not the 

 alkyl carhon and oxygen. This is based on the following observations 

 (Hammett, 1940, p. 354). 



(a) Using amyl acetate in water containing labeled oxygen (O^^), 

 Polanyi and Szabo (1934) showed that oxygen of the alcohol formed 

 by the alkaline hydrolysis of the ester is the original ester oxygen and 

 did not come from the water. 



(b) Alkaline hydrolysis of an ester containing an optically active 

 alkyl group does not yield an inverted carbinol as should be expected 

 if the bond between the oxygen and the asymmetric carbon of the alkyl 

 group had been ruptured. 



(c) No rearrangement takes place during the hydrolysis if the 

 alcohol part of the ester consists of an a-, ^S-unsaturated alcohol, thus 

 eliminating the carbonium type reaction. 



