key term - Hydride Reducing Agent

Definition

A hydride reducing agent is a compound that can donate a hydride ion (H-) to reduce carbonyl compounds, such as aldehydes and ketones, to alcohols. These reducing agents are commonly used in the context of 17.4 Alcohols from Carbonyl Compounds: Reduction, where they facilitate the conversion of carbonyl groups to hydroxyl groups.

5 Must Know Facts For Your Next Test

1. Hydride reducing agents, such as sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4), are commonly used in organic chemistry to reduce carbonyl compounds to alcohols.
2. The hydride ion (H-) acts as a nucleophile, attacking the electrophilic carbon of the carbonyl group and forming a tetrahedral intermediate, which is then converted to an alcohol.
3. Sodium borohydride (NaBH4) is a milder reducing agent and is typically used to reduce aldehydes and ketones, while lithium aluminum hydride (LiAlH4) is a stronger reducing agent and can also reduce esters and carboxylic acids.
4. The choice of hydride reducing agent depends on the specific functional groups present in the molecule and the desired selectivity of the reduction.
5. Hydride reducing agents are often used in the context of 17.4 Alcohols from Carbonyl Compounds: Reduction, where they play a crucial role in the conversion of carbonyl compounds to alcohols, a common transformation in organic synthesis.

Review Questions

• Explain the mechanism of how a hydride reducing agent, such as sodium borohydride (NaBH4), reduces a carbonyl compound to an alcohol.
  • In the mechanism of hydride reduction, the hydride ion (H-) from the reducing agent, such as sodium borohydride (NaBH4), acts as a nucleophile and attacks the electrophilic carbon of the carbonyl group. This forms a tetrahedral intermediate, which is then protonated to give the corresponding alcohol. The oxygen atom of the carbonyl group accepts the hydride, leading to the reduction of the carbonyl to a hydroxyl group. This process is a key step in the conversion of carbonyl compounds to alcohols, as seen in the context of 17.4 Alcohols from Carbonyl Compounds: Reduction.
• Compare and contrast the use of sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4) as hydride reducing agents, and explain how the choice of reducing agent can affect the selectivity of the reduction.
  • Sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4) are both hydride reducing agents, but they differ in their reducing strength and selectivity. Sodium borohydride is a milder reducing agent and is typically used to reduce aldehydes and ketones to alcohols, while maintaining the integrity of other functional groups. In contrast, lithium aluminum hydride is a stronger reducing agent and can also reduce esters and carboxylic acids to alcohols. The choice of reducing agent depends on the specific functional groups present in the molecule and the desired selectivity of the reduction. For example, if the molecule contains a carbonyl group and an ester group, lithium aluminum hydride would be the preferred reducing agent, as it can reduce both functionalities, whereas sodium borohydride would only reduce the carbonyl group, leaving the ester group intact.
• Evaluate the role of hydride reducing agents in the context of 17.4 Alcohols from Carbonyl Compounds: Reduction, and discuss how the use of these reagents contributes to the broader goals of organic synthesis.
  • Hydride reducing agents play a crucial role in the context of 17.4 Alcohols from Carbonyl Compounds: Reduction, as they facilitate the conversion of carbonyl compounds, such as aldehydes and ketones, to alcohols. This transformation is a fundamental reaction in organic synthesis, as alcohols are versatile building blocks that can be further functionalized or incorporated into more complex molecules. The use of hydride reducing agents, such as sodium borohydride and lithium aluminum hydride, allows for the selective reduction of carbonyl groups, while preserving other functional groups in the molecule. This selectivity is essential in organic synthesis, where the ability to manipulate specific functional groups is crucial for the construction of more complex organic compounds. By enabling the conversion of carbonyl compounds to alcohols, hydride reducing agents contribute to the broader goals of organic synthesis, which include the efficient and selective synthesis of target molecules with desired properties and functionalities.

Related terms

Nucleophilic Addition:

The addition of a nucleophile, such as a hydride, to the electrophilic carbon of a carbonyl compound, resulting in the formation of a tetrahedral intermediate.

Reduction:

A chemical reaction that involves the gain of electrons, leading to a decrease in oxidation state of the reactants.

Carbonyl Compound:

An organic compound containing a carbon-oxygen double bond, including aldehydes and ketones, which can be reduced to alcohols using hydride reducing agents.