Hydrolysis and Alcoholysis of Esters

The hydrolysis of carboxylic esters can in principle take place either as carboxyl-O cleavage, i.e., as an SN reaction at the carboxyl carbon— 

The hydrolysis is generally not carried out at pH 7 but is either acid-catalyzed or base-mediated (i.e., as a so-called saponification). Base-catalyzed ester hydrolyses do not exist The carboxylic acid produced protonates a full equivalent of base and thus consumes it. 

Driving Force of Base-Mediated and Acid-Catalyzed Ester Hydrolyses 

Base-mediated ester hydrolyses have a high driving force. This is because of the acid/base reaction between the carboxylic acid formed in the reaction, and the base used as the reagent. The resonance stabilization of the carboxylate is approximately 30 kcal/mol, which means a gain of about 16 kcal/mol compared to the starting material, the carboxylic ester (resonance stabilization 14 kcal/mol according to Table 6.1). Accordingly, the hydrolysis equilibrium lies completely on the side of the carboxylate. 

The mechanisms of ester hydrolysis are distinguished with abbreviations of the type medium.. .., . , , reaction order. The medium of acid-catalyzed hydroly- 

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