Reactions at the Carbonyl Carbon of Acid Derivatives

Hydrolysis of most acid derivatives to the parent acids is acid- or base-catalyzed  

However, acyl halides and anhydrides usually hydrolyze rapidly without the aid of an acidic or basic catalyst, when in solution. It is important to recognize that an insoluble acyl halide or anhydride often reacts slowly with water. 

Esters and amides hydrolyze much more slowly, and for useful rates require a catalyst. The hydrolysis of amides is of exceptional importance in biochemistry and will be discussed in more detail in Chapters 24 and 25. 

Acid-catalyzed hydrolysis of esters is the reverse of acid-catalyzed ester formation discussed previously. Base-induced ester hydrolysis (saponification) is an irreversible reaction. The initial step is the attack of hydroxide ion at the carbonyl carbon  

The intermediate anion, 13, so formed then either loses OHG and reverts to the original ester, or it loses CH3Oeto form the acid. The overall reaction is irreversible because once the acid is formed, it immediately is converted to the carboxylate anion, which is stabilized to such a degree that it is not attacked by the alcohol and will not reform the starting ester. Consequently, the reaction goes to completion in the direction of hydrolysis  

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