Reactions

The only ester reaction that we will deal with in this lesson is the hydrolysis reaction. It is shown here in general form (and a specific example is shown in Example 15-a in your workbook). In addition, there are variations of this reaction with which you should be familiar.

Equation showing the hydrolysis of an ester. [64rxn12.JPG]

First of all, note that the reaction is simply a reversal of the formation of an ester by the intermolecular dehydration of an acid and an alcohol. It is a reversible reaction. It is an equilibrium reaction. Which way it goes and how far depends on the conditions of the reaction and the concentrations of the chemicals involved. At best you get a mixture of chemicals which have to be separated from one another.

One of the important conditions is the pH of the reaction mixture. As is shown here in the middle equation (and in Example 15-b in your workbook), if the hydrolysis takes place in an acidic solution, the products are a carboxylic acid and an alcohol. On the other hand, if the reaction takes place in basic solution, as shown here in the bottom equation (and in Example 15-c), the products are a carboxylate ion and an alcohol.

Equations showing hydrolysis of an ester under acidic and basic conditions. [64rxn14.JPG]

Sometimes it is not important to be aware of what form the product takes, whether it is a carboxylic acid molecule or a carboxylate ion. When it is not important to make that distinction, the standard molecular equation for hydrolysis reaction shown at the top of the page is the easiest to use. If the distinction and the reaction conditions are important, then use equations like the lower ones as appropriate.

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E-mail instructor: Sue Eggling

Clackamas Community College
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