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Ch. 21 - Carboxylic Acid Derivatives
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Non è quello che usi tu?Cambia libro di testo
Capitolo 21, Problema 24b

Propose a mechanism for the reduction of octanoyl chloride by lithium aluminum hydride.

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Step 1: Recognize the functional groups involved. Octanoyl chloride is an acyl chloride, which is a reactive carboxylic acid derivative. Lithium aluminum hydride (LiAlH₄) is a strong reducing agent commonly used to reduce acyl chlorides to primary alcohols.
Step 2: Initiate the mechanism by identifying the nucleophilic attack. The hydride ion (H⁻) from LiAlH₄ acts as a nucleophile and attacks the carbonyl carbon of the octanoyl chloride. This forms a tetrahedral intermediate. Represent this step using the chemical equation: R-COCloctanoyl+Hhydride→R-COHtetrahedral
Step 3: Describe the collapse of the tetrahedral intermediate. The intermediate collapses, expelling the chloride ion (Cl⁻) as a leaving group. This results in the formation of an aldehyde intermediate. Represent this step using the chemical equation: R-COHtetrahedral→R-CHOaldehyde+Clleaving
Step 4: Explain the second reduction step. Another hydride ion (H⁻) from LiAlH₄ attacks the aldehyde intermediate, forming a second tetrahedral intermediate. This intermediate eventually collapses to yield the primary alcohol. Represent this step using the chemical equation: R-CHOaldehyde+Hhydride→R-CH₂OHprimary
Step 5: Summarize the overall reaction. The reduction of octanoyl chloride by LiAlH₄ proceeds through two key steps: (1) reduction to an aldehyde intermediate, and (2) further reduction to a primary alcohol. The final product is octanol, a primary alcohol. Ensure to balance the reaction and account for all byproducts such as Cl⁻.

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Reduction Reactions

Reduction reactions involve the gain of electrons or the decrease in oxidation state by a molecule. In organic chemistry, this often refers to the conversion of carbonyl compounds, like acyl chlorides, into alcohols. Understanding the principles of reduction is essential for proposing mechanisms, as it dictates how reactants interact and transform.
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Lithium Aluminum Hydride (LiAlH4)

Lithium aluminum hydride is a powerful reducing agent commonly used in organic synthesis. It can donate hydride ions (H-) to electrophilic centers, such as carbonyl groups, facilitating their reduction. Recognizing its reactivity and mechanism of action is crucial for understanding how it reduces octanoyl chloride to octanol.
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Mechanism of Nucleophilic Acyl Substitution

The mechanism of nucleophilic acyl substitution describes how nucleophiles attack acyl compounds, leading to the replacement of a leaving group. In the case of octanoyl chloride, the hydride from LiAlH4 acts as a nucleophile, attacking the carbonyl carbon and forming an alkoxide intermediate. This concept is vital for detailing the stepwise process of the reduction.
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Nucleophiles and Electrophiles can react in Substitution Reactions.