Oxygen compounds ester hydrolysis

Acid-Catalyzed Hydrolysis. In acid-catalyzed ester hydrolysis the species that undergoes the rate-determining step is the protonated ester (Fig. 13.10). When the molecule is in this protonated form, the enhanced depletion of electrons near the central carbon promotes the approach of an electron-rich oxygen of a water molecule. Hence, the hydrolysis rate depends on the fraction of compound molecules that are protonated. This fraction, in turn, depends on how strong a base the ester function is. If we define an acidity constant (see Chapter 8) for the protonated species... 

Under acidic or basic conditions, the rate of hydrolysis is enhanced. Under acidic conditions, the hydrolysis involved protonation of the in-chain oxygen atom of the ester function followed by reaction with water to produce hydroxyl and carboxyl end groups compounds. Under basic conditions, the hydroxide anion attacks the carbonyl oxygen atom to produce same compounds. The hydrolysis reaction can be followed by measuring the increase in the concentration of carboxyl ends with time by using classical end group analysis (14,15). 

The production of both an alcohol and the sodium salt of an acid might easily be confused with the hydrolysis products of an ester (in the above instance benzyl benzoate). Such an error would soon be discovered (e.g., by reference to the b.p. and other physical properties), but it would lead to an unnecessary expenditure of time and energy. The above example, however, emphasises the importance of conducting the class reactions of neutral oxygen-containing compounds in the proper order, viz., (1) aldehydes and ketones, (2) esters and anhydrides, (3) alcohols, and (4) ethers. 

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