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17.4: Hydrolysis of Esters and Amides

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    86298
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    Learning Objectives
    • Describe the typical reaction that takes place with esters.
    • Identify the products of an acidic hydrolysis of an ester.
    • Identify the products of a basic hydrolysis of an ester.

    Esters are neutral compounds, unlike the acids from which they are formed. In typical reactions, the alkoxy (OR′) group of an ester is replaced by another group. One such reaction is hydrolysis, literally “splitting with water.” The hydrolysis of esters is catalyzed by either an acid or a base.

    Acidic hydrolysis is simply the reverse of esterification. The ester is heated with a large excess of water containing a strong-acid catalyst. Like esterification, the reaction is reversible and does not go to completion.

    acid hydrolysis.jpg

    As a specific example, butyl acetate and water react to form acetic acid and 1-butanol. The reaction is reversible and does not go to completion.

    butyl acetate.jpg
    Example \(\PageIndex{1}\)

    Write an equation for the acidic hydrolysis of ethyl butyrate (CH3CH2CH2COOCH2CH3) and name the products.

    Solution

    Remember that in acidic hydrolysis, water (HOH) splits the ester bond. The H of HOH joins to the oxygen atom in the OR part of the original ester, and the OH of HOH joins to the carbonyl carbon atom:

    Ex 7.jpg

    The products are butyric acid (butanoic acid) and ethanol.

    Exercise \(\PageIndex{1}\)

    Write an equation for the acidic hydrolysis of methyl butanoate and name the products.

    When a base (such as sodium hydroxide [NaOH] or potassium hydroxide [KOH]) is used to hydrolyze an ester, the products are a carboxylate salt and an alcohol. Because soaps are prepared by the alkaline hydrolysis of fats and oils, alkaline hydrolysis of esters is called saponification (Latin sapon, meaning “soap,” and facere, meaning “to make”). In a saponification reaction, the base is a reactant, not simply a catalyst. The reaction goes to completion:

    saponification.jpg

    As a specific example, ethyl acetate and NaOH react to form sodium acetate and ethanol:

    ethyl acetate.jpg
    Example \(\PageIndex{2}\)

    Write an equation for the hydrolysis of methyl benzoate in a potassium hydroxide solution.

    Solution

    In basic hydrolysis, the molecule of the base splits the ester linkage. The acid portion of the ester ends up as the salt of the acid (in this case, the potassium salt). The alcohol portion of the ester ends up as the free alcohol.

    Ex 8.jpg
    Exercise \(\PageIndex{2}\)

    Write the equation for the hydrolysis of ethyl propanoate in a sodium hydroxide solution.

    Hydrolysis of Amides

    Generally, amides resist hydrolysis in plain water, even after prolonged heating. In the presence of added acid or base, however, hydrolysis proceeds at a moderate rate. In living cells, amide hydrolysis is catalyzed by enzymes. Amide hydrolysis is illustrated in the following example:

    clipboard_e69269df5e39caed767729fe18f975623.png

    Hydrolysis of an amide in acid solution actually gives a carboxylic acid and the salt of ammonia or an amine (the ammonia or amine initially formed is neutralized by the acid). Basic hydrolysis gives a salt of the carboxylic acid and ammonia or an amine.

    Example \(\PageIndex{1}\)

    Write the equation for the hydrolysis of each compound.

    1. butyramide
    2. benzamide
    Solution
    1. The hydrolysis of a simple amide produces an organic acid and ammonia. Butyramide thus yields butyric acid and ammonia.
      clipboard_e6a555005fad0de25363fad726d6de540.png
    • The hydrolysis of an amide produces an organic acid and ammonia. Benzamide thus yields benzoic acid and ammonia.
      clipboard_e40233ea6fc0a21cf529059999426e7cc.png
    Exercise \(\PageIndex{1}\)

    Write the equation for the hydrolysis of each compound.

    1. propionamide (propanamide)
    2. hexanamide
    Career Focus: Athletic Trainer

    Athletic training is an allied health-care profession recognized by the American Medical Association. The athletic trainer’s role is to recognize, evaluate, and provide immediate care for athletic injuries; prevent athletic injuries by taping, bandaging, and bracing vulnerable body parts; make referrals to medical doctors when necessary; and rehabilitate injured athletes. Athletic trainers work in high schools, colleges, and other organizations where athletics programs are found. Athletic trainers usually have a degree from an accredited athletic training program whose curriculum includes such basic science courses as biology, chemistry, and physics. These studies provide the necessary background for more applied courses, such as anatomy and physiology, exercise physiology, kinesiology, and nutrition. Knowledge of chemistry is necessary for understanding pharmacological and medical terminology. For example, athletic trainers must understand the action of numerous drugs, many of which are esters, amines, or amides like those mentioned in this chapter.

    Athletic trainers may have administrative duties, such as the responsibility for ordering supplies. They also need to be able to evaluate nutritional supplements because providing the wrong one can get an athlete banned from competition and may bring sanctions against a school. In short, the athletic trainer is responsible for the overall health and well-being of the athletes in his or her charge.

    Summary

    Hydrolysis is a most important reaction of esters. Acidic hydrolysis of an ester gives a carboxylic acid and an alcohol. Basic hydrolysis of an ester gives a carboxylate salt and an alcohol.


    17.4: Hydrolysis of Esters and Amides is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by LibreTexts.

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