What products are obtained from the reaction of the following compounds with LiAlH4 followed by treatment with dilute acid?a. ethyl butanoateb. benzoic acid

Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives

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Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives

Problem 21a,b

Chapter 17, Problem 21a,b

What products are obtained from the reaction of the following compounds with LiAlH₄ followed by treatment with dilute acid?
a. ethyl butanoate
b. benzoic acid

Verified step by step guidance

Step 1: Understand the role of LiAlH4 (Lithium Aluminum Hydride). LiAlH4 is a strong reducing agent commonly used to reduce esters, carboxylic acids, aldehydes, and ketones to their corresponding alcohols. The reaction typically involves two steps: reduction with LiAlH4 and subsequent hydrolysis with dilute acid to complete the reaction.

Step 2: Analyze the structure of ethyl butanoate. Ethyl butanoate is an ester with the general formula RCOOR'. When treated with LiAlH4, the ester bond is cleaved, reducing the carbonyl group (C=O) to a primary alcohol (RCH2OH) and the alkoxy group (R'OH) to an alcohol. Write the reaction as: \( \text{CH3CH2CH2COOCH2CH3} \xrightarrow{LiAlH4} \text{CH3CH2CH2CH2OH + CH3CH2OH} \).

Step 3: Analyze the structure of benzoic acid. Benzoic acid is a carboxylic acid with the formula \( \text{C6H5COOH} \). When treated with LiAlH4, the carboxylic acid group (COOH) is reduced to a primary alcohol (CH2OH). Write the reaction as: \( \text{C6H5COOH} \xrightarrow{LiAlH4} \text{C6H5CH2OH} \).

Step 4: Understand the role of dilute acid in the reaction. After the reduction step with LiAlH4, the reaction mixture is treated with dilute acid (e.g., H2O or HCl) to hydrolyze any intermediate aluminum complexes and release the final alcohol products.

Step 5: Summarize the products. For ethyl butanoate, the products are butanol (\( \text{CH3CH2CH2CH2OH} \)) and ethanol (\( \text{CH3CH2OH} \)). For benzoic acid, the product is benzyl alcohol (\( \text{C6H5CH2OH} \)).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reduction Reactions

Reduction reactions involve the gain of electrons or the decrease in oxidation state by a molecule. In organic chemistry, reducing agents like lithium aluminum hydride (LiAlH4) are commonly used to convert carbonyl compounds, such as esters and carboxylic acids, into alcohols. Understanding how these reactions proceed is crucial for predicting the products formed.

LiAlH4 as a Reducing Agent

Lithium aluminum hydride (LiAlH4) is a powerful reducing agent that can reduce a wide range of functional groups, including esters and carboxylic acids. When LiAlH4 reacts with these compounds, it typically converts them into their corresponding alcohols. This concept is essential for determining the products of the reactions mentioned in the question.

Acid Workup

An acid workup is a common procedure following a reduction reaction, where dilute acid is added to neutralize excess reducing agent and protonate the resulting alkoxide intermediates. This step is crucial for converting the alkoxide into the final alcohol product. Understanding this process helps in predicting the final products after the reaction with LiAlH4.

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