22 IMMUNO-CATALYSIS 



The hydrolysis of the esters derived from tertiary butyl alcohol 

 forms an exception to the above mechanism in that the alkyl-oxygen 

 linkage rather than the acyl-oxygen linkage is ruptured, as shown 

 below. 



CHs CH3 



: I HOH I 



R— C— O C— CH3 > R— C— OH + HO— C— CH, 



II : I II I 



O CHs O CHs 



(Cohen and Schneider, 1941) 

 The hydrolysis can be represented as follows: 



10— H 



R— C— C— R, + 1 10— H I I > • R— C-^i :^ 



lOi *- ^Q— Ri 



-Ri + |iQ-H I 



R— C=0 + 10— Ri HOH^ ROH + OH~ 

 10— H 



Alkaline hydrolysis of an ester is practically irreversible on account 

 of the exhaustion of the anion due to the reaction : 



R— C— OH + NaOH > R— C— O" + Na+ + H2O 



II 11 



O O 



As an exception to this mechanism, in esters of sulphuric and sul- 

 phonic acids it is the alkyl oxygen linkage that is severed. In fact, these 

 esters are used as alkylating agents. 



g. Acid Catalyzed Esterification and Hydrolysis. Acid catalyzed 

 esterification and hydrolysis are reversible and may go towards comple- 

 tion either to the right or left depending upon the excess of water or 

 alcohol. In hydrolysis, the alkyl-oxygen link is not the one that is 

 severed (Roberts and Urey, 1938, 1939), since it is shown by labeled 

 oxygen studies that in esterification the ether oxygen of the ester comes 

 from alcohol as shown below (Hammett, 1940, pp. 356-357). 



CeHs— C— Oi«H+CH30»«H ^CgHsC— O^s— CHs+HzQi^ 



II II 



O" Oi« 



