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Chapter 21: Problem 502

Indicating the mechanism, show how ethyl propionate may be prepared from propionic acid.

Short Answer

Expert verified
Ethyl propionate can be prepared from propionic acid through the Fischer esterification reaction. This involves reacting propionic acid with ethanol in the presence of a strong acid catalyst. The reaction mechanism includes the protonation of the carbonyl group, nucleophilic attack by ethanol, proton transfer, elimination of water, and deprotonation to form ethyl propionate and water. The overall reaction is: \[ \text{Propionic acid} + \text{Ethanol} \xrightarrow{\text{H+ catalyst}} \text{Ethyl Propionate} + \text{Water} \]

Step by step solution

01

Identify the reactants

Propionic acid (a carboxylic acid) reacts with an alcohol to form ethyl propionate (an ester). To determine the specific alcohol needed, we look at the structure of ethyl propionate to determine that we need ethanol. Therefore, the reactants are propionic acid and ethanol.
02

Protonation of the carbonyl group

\[ \text{Propionic acid} + \text{Ethanol} \rightarrow \text{Ethyl Propionate} + \text{Water} \] In the presence of a strong acid catalyst, the carbonyl group (C=O) of the propionic acid is protonated. This step makes the carbonyl carbon more electrophilic and susceptible to nucleophilic attack. \[\text{C=O} + \text{H}^{+} \rightarrow \text{C\(^+\)=OH}\]
03

Nucleophilic attack by alcohol

The nucleophilic oxygen atom in the ethanol molecule attacks the electrophilic carbon atom in the protonated propionic acid. This forms a tetrahedral intermediate with a positively charged oxygen atom. \[\text{C\(^+\)=OH} + \text{Ethanol} \rightarrow \text{Oxygen-Carbon-Oxygen-H\(^+\)} \]
04

Proton transfer

The positively charged oxygen atom from the previous intermediate donates a proton to a nearby alcohol molecule (or any other available base). This results in the formation of a hydroxyl group and an oxonium ion. \[\text{Oxygen-Carbon-Oxygen-H\(^+\)} \rightarrow \text{Oxygen-Carbon-Oxygen-H} + \text{H3O\(^+\)} \]
05

The elimination of water

In this step, a molecule of water (H2O) is eliminated from the intermediate, generating a carbocation. \[\text{Oxygen-Carbon-Oxygen-H} \rightarrow \text{Carbocation} + \text{Water}\]
06

Deprotonation and ester formation

Finally, the carbocation formed in the previous step is deprotonated by an alcohol molecule (or any other available base) to form ethyl propionate and a hydronium ion, completing the Fischer esterification reaction. \[\text{Carbocation} + \text{Ethanol} \rightarrow \text{Ethyl Propionate} + \text{H3O\(^+\)}\] The overall reaction is: \[\text{Propionic acid} + \text{Ethanol} \xrightarrow{\text{H+ catalyst}} \text{Ethyl Propionate} + \text{Water}\]

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Most popular questions from this chapter

Write equations to show the reaction of benzoic anhydride with: (a) water, (b)ethyl alcohol, and (c) aniline.

Write equations to show the reaction of acetyl chloride with: (a) water, (b) ammonia, and (c) isopropyl alcohol.

(a) What is the saponification equivalent of n-propyl acetate? (b) There are eight other simple aliphatic esters that have the same saponification equivalent. What are they? (c) In contrast, how many simple aliphatic acids have this equivalent weight? (d) Is saponification equivalent as helpful in identification as neutralization equivalent?

Describe simple chemical tests that would serve to dis tinguish between: (a) propionic acid and methyl acetate (b) n-butyryl chloride and n-butyl chloride (c) \(\mathrm{p}\) -nitrobenzamide and ethyl \(\mathrm{p}\) -nitrobenzoate (d) glyceryl tristearate and glyceryl trioleate (e) benzonitrile and nitrobenzene (f) acetic anhydride and \(\mathrm{n}\) -butyl alcohol (g) glyceryl monopalmitate and glyceryl tripalmitate (h) ammonium benzoate and benzamide (i) \(\mathrm{p}\) -bromobenzoic acid and benzoyl bromide Tell exactly what you would do and see.

Fumaric and maleic acid give the same anhydride on heating, but fumaric acid must be heated to much higher temperatures than maleic acid to effect the same change. Explain. Write reasonable mechanism for both reactions.
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