Carbonyl Oxygen Exchange in General Base Catalyzed Ester Hydrolysis

1967 ◽  
Vol 89 (5) ◽  
pp. 1211-1220 ◽  
Author(s):  
Myron L. Bender ◽  
Henry d'A. Heck
Keyword(s):  
Carbonyl Oxygen ◽  
Ester Hydrolysis ◽  
Oxygen Exchange ◽  
General Base

Carbonyl oxygen exchange of glycol monoesters. Rate and equilibrium constants for the formation of a tetrahedral intermediate

1979 ◽  
Vol 57 (12) ◽  
pp. 1531-1540 ◽  
Author(s):  
R. A. McClelland ◽  
M. Ahmad ◽  
J. Bohonek ◽  
S. Gedge
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Carbonyl Oxygen ◽  
Ester Hydrolysis ◽  
Oxygen Exchange ◽  
Ortho Ester ◽  
Kinetic Investigations ◽  
Relationship Of ◽  
The Relationship

Kinetic investigations of the hydrolysis of the 2-phenyl-4,4,5,5-tetramethyl-1,3-dioxolenium ion and 2-phenyl-2-methoxy-4,4,5,5-tetramethyl-1,3-dioxolane furnish rate constants for all three reaction stages of the ortho ester hydrolysis: (1) generation of the dioxolenium ion, (2) hydration of this ion to form hydrogen ortho ester, and (3) breakdown of this species to pinacol monobenzoate. The equilibrium constant for stage (2) can also be obtained. This study complements a previous investigation of 2-phenyl-2-alkoxy-1,3-dioxolanes where similar information was obtained.The rate constants for carbonyl oxygen exchange of the ester products of these reactions, pinacol monobenzoate and ethylene glycol monobenzoate, have been measured. This reaction is shown to proceed by a different mechanism to that normally associated with exchange of carboxylic acid derivatives: cyclization of the glycol monoester to form hydrogen ortho ester, followed by loss of the labelled exocyclic OH group to give 1,3-dioxolenium ion. Reversal of these steps, initiated by an unlabelled water molecule, results in exchange. The relationship of this mechanism with that of the ortho ester hydrolysis is obvious; it is shown that the exchange provides rate constants for the reverse of stage (3). This means that both the forward and reverse rates of this process have been obtained, and this provides the equilibrium constant.

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