Question

What product would you expect from the reaction of butyrolactone with LiAlH \(_{4}\) ? With DIBAH?

Short answer

LiAlH\(_4\) gives 1,4-butanediol; DIBAH gives butyraldehyde.

Step-by-step solution

Understand the Reagents and Substrate

LiAlH\(_4\) is a strong reducing agent commonly used to reduce esters, carboxylic acids, and lactones to alcohols. DIBAH (Diisobutylaluminum hydride) is a selective reducing agent often used to reduce esters and lactones to aldehydes.

Analyze the Structure of Butyrolactone

Butyrolactone is a cyclic ester (also known as a lactone) derived from gamma-hydroxybutyric acid. It has a four-membered ring structure containing one oxygen atom. It can undergo reduction reactions to open the ester ring.

Predict the Product with LiAlH_4

When butyrolactone is treated with LiAlH\(_4\), the strong reducing agent fully reduces the lactone ring, leading to the formation of a primary alcohol. This reaction opens the lactone ring, converting it into a compound with an alcohol group at each end of the former ester.

Predict the Product with DIBAH

When butyrolactone is treated with DIBAH, the reagent selectively reduces the lactone to an aldehyde. In this case, the lactone ring is cleaved at the ester bond, forming a linear molecule that contains an aldehyde group instead of a full reduction to an alcohol.

Write the Expected Products for Each Reaction

For butyrolactone with LiAlH\(_4\), the expected product is 1,4-butanediol. For butyrolactone with DIBAH, the expected product is butyraldehyde.

Key concepts

LiAlH4 Reduction

LiAlH\(_4\) is a powerful reducing agent commonly used in organic chemistry to reduce various compound classes. Its primary application is breaking down complex molecules into simpler alcohol forms.

• Strong Reactivity: LiAlH\(_4\) is highly effective at reducing esters, carboxylic acids, and lactones to alcohols.
• Mechanism of Action: It donates hydride ions (H\(^-\)) to the carbonyl carbon, disrupting the carbonyl structure and forming alcohol groups.

This reagent's strong reducing power comes from its ability to transport the substantial negative charge needed to convert carbon-oxygen double bonds into single bonds with additional hydrogen atoms. In the context of lactones like butyrolactone, LiAlH\(_4\) transforms the cyclic ester into a linear diol, changing the molecular architecture dramatically.

DIBAH Reduction

DIBAH, short for diisobutylaluminum hydride, is renowned for its selective reduction properties. Unlike LiAlH\(_4\), DIBAH allows for controlled reduction processes, making it invaluable for obtaining specific products such as aldehydes.

• Selective Nature: DIBAH selectively reduces esters and lactones, stopping at the aldehyde stage rather than proceeding to alcohols.
• Reaction Specificity: Particularly useful for chemists aiming to avoid over-reduction in synthetic pathways.

By providing a gentler reduction approach than LiAlH\(_4\), DIBAH maintains more of the original molecular structure, making it an ideal choice for the formation of aldehydes from cyclic compounds like butyrolactone.

Lactone Chemistry

Lactones are cyclic esters, which are common in various biochemical processes and industrial applications. Their unique ring structures can undergo specific reactions, exploited in reductions.

• Cyclic Structure: Lactones are characterized by an ester linkage within a ring structure, typically involving four or more atoms.
• Reactivity: The strain in smaller lactone rings, such as butyrolactone, makes them susceptible to reactions that open the ring.

In reduction reactions, lactones can be opened to form more linear products, transforming them into esters or alcohols, depending on the reducing agent used.

Ester Reduction

Ester reduction is a crucial process in organic chemistry, transforming esters into alcohols or aldehydes through the addition of hydrogen.

• Hydride Donor: Reducing agents like LiAlH\(_4\) donate hydride ions, cleaving the ester bond.
• Pathway and Products: The reduction can fully convert esters into primary alcohols when strong reducers are used.

This transformation is essential in synthesizing organic compounds used in fragrances, flavorings, and pharmaceuticals, as the reduced alcohols or aldehydes form building blocks for more complex molecules. Control over these reactions is achieved by choosing the appropriate reducing agent.

Alcohol Formation

Alcohol formation from esters or lactones involves reducing these compounds, resulting in the production of alcohols. This process is a staple in converting more complex molecules to simpler, more reactive forms.

• Full Reduction: With agents like LiAlH\(_4\), esters are fully reduced to alcohols.
• Applications: Useful in multiple industrial processes, including the production of solvents and intermediates.

The ability to reduce esters to alcohols allows chemists to manipulate molecular structures to suit needs for synthesis in both small-scale and large-scale applications. The choice of reducing agent determines whether the reaction proceeds fully or stops at the aldehyde stage.

Aldehyde Formation

Aldehyde formation is an intermediate step that can be achieved through the partial reduction of esters and lactones, using less aggressive reducing agents.

• Controlled Reduction: Agents like DIBAH are leveraged to halt reductions at the aldehyde level.
• Intermediate Products: Aldehydes serve as key intermediates due to their reactivity, providing routes to further chemical modifications.

Producing aldehydes from lactones like butyrolactone is particularly significant in organic synthesis, enabling pathways to more complex molecules such as alcohols or acids, depending on subsequent steps employed.