Textbook Question
Show how the following ketones might be synthesized from the indicated acids, using any necessary reagents.
(a) propiophenone from propionic acid (using Friedel–Crafts acylation)
22. Carboxylic Acid Derivatives: NAS
Nucleophilic Acyl Substitution
1:47 minutesProblem 54a
Textbook Question
Show how you would accomplish the following syntheses. Some of these conversions may require more than one step.
(a) isopentyl alcohol → isopentyl acetate (banana oil)
Verified step by step guidance1
Identify the functional group transformation: The conversion involves transforming isopentyl alcohol (an alcohol) into isopentyl acetate (an ester). This is a classic esterification reaction.
Choose the appropriate reagents: To synthesize an ester from an alcohol, you can use acetic acid (CH₃COOH) and a strong acid catalyst, such as sulfuric acid (H₂SO₄), in a Fischer esterification reaction.
Write the reaction mechanism: The alcohol (isopentyl alcohol) reacts with acetic acid in the presence of the acid catalyst. The hydroxyl group (-OH) from the alcohol and a hydrogen atom from the carboxylic acid combine to form water (H₂O), leaving behind the ester bond.
Set up the reaction conditions: Mix isopentyl alcohol and acetic acid in a 1:1 molar ratio, add a few drops of concentrated sulfuric acid as the catalyst, and heat the mixture under reflux to drive the reaction to completion.
Isolate and purify the product: After the reaction is complete, use techniques such as extraction to separate the ester layer, followed by washing with water and drying over an anhydrous agent. Finally, distill the product to obtain pure isopentyl acetate.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Esterification
Esterification is a chemical reaction that forms an ester from an alcohol and a carboxylic acid. In the case of synthesizing isopentyl acetate from isopentyl alcohol, the reaction involves combining isopentyl alcohol with acetic acid, typically in the presence of an acid catalyst, to facilitate the reaction and drive it to completion.
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Reflux
Reflux is a technique used in organic chemistry to heat a reaction mixture while preventing the loss of volatile components. This is achieved by using a condenser to cool and return vapors back to the reaction vessel. In the synthesis of isopentyl acetate, refluxing the mixture of isopentyl alcohol and acetic acid ensures that the reaction proceeds efficiently and that the reactants remain in contact for an adequate time.
Reaction Mechanism
Understanding the reaction mechanism is crucial for predicting the steps involved in the conversion of reactants to products. In the esterification of isopentyl alcohol to isopentyl acetate, the mechanism involves protonation of the alcohol, nucleophilic attack by the alcohol on the carbonyl carbon of the acetic acid, and subsequent elimination of water to form the ester. Familiarity with these steps aids in optimizing conditions for the synthesis.
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