Question

Derive an alcohol product from the following aldehyde precursors using any reagents and conditions necessary.

Short answer

The alcohol product derived from an aldehyde precursor \( R-CHO \) can be obtained by performing a reduction reaction using Sodium Borohydride (NaBH4) as a reducing agent in a polar protic solvent under ice-cold conditions, followed by protonation of the resulting alkoxide ion intermediate with an acid. The final alcohol product is \( R-CH(OH) \), where "R" represents any alkyl or aryl group, and "CH(OH)" represents an alcohol functional group.

Step-by-step solution

Write down the given aldehyde precursor

First, let's write down the aldehyde precursor whose structure is: \( R-CHO \) Where "R" represents any alkyl or aryl group, and "CHO" represents an aldehyde functional group.

Identify the reducing agent and conditions

We'll use Sodium Borohydride (NaBH4) as the reducing agent in this reduction reaction. The conditions for this reaction are a polar protic solvent, such as ethanol or methanol, and ice-cold temperatures.

Perform the reduction reaction

Next, we'll perform the reduction reaction by treating the aldehyde precursor with the reducing agent (NaBH4) in the polar protic solvent under ice-cold conditions. The general reaction scheme can be written as: \( R-CHO + NaBH_4 \rightarrow R-CH(O^-)Na + BH_3 \) In this step, the reducing agent (NaBH4) donates a hydride ion (H-) to the carbonyl carbon of the aldehyde, leading to the formation of an alkoxide ion intermediate (R-CH(O-)). At the same time, sodium ions (Na+) and borane (BH3) are generated as byproducts.

Protonate the alkoxide ion intermediate

The last step of the reaction is to protonate the alkoxide ion intermediate (R-CH(O-)) in order to form an alcohol product. This can be achieved using an acid, such as water or dilute hydrochloric acid (HCl), as a proton source: \( R-CH(O^-) + H_3O^+ \rightarrow R-CH(OH) + H_2O \) Here, the alkoxide ion receives a proton (H+) from the acid, resulting in the formation of an alcohol product (R-CH(OH)) and water as the byproduct.

Write down the final alcohol product

After completing the reduction reaction and protonation steps, we have derived an alcohol product from the given aldehyde precursor. The final alcohol product is: \( R-CH(OH) \) where "R" represents any alkyl or aryl group, and "CH(OH)" represents an alcohol functional group. In conclusion, we have successfully derived an alcohol product from the aldehyde precursor by performing a reduction reaction using Sodium Borohydride (NaBH4) as a reducing agent and then protonating the resulting alkoxide ion with an acid.

Key concepts

Alcohol Formation

Alcohol formation is a key process in organic chemistry, essential for both synthetic and biological reactions. An alcohol is characterized by an -OH (hydroxyl) group attached to a carbon atom. The transformation of aldehydes to alcohols involves two main steps: reduction and protonation.

• Reduction: This step involves the conversion of the carbonyl group (C=O) in an aldehyde to a hydroxyl group (C-OH).
• Protonation: After the reduction, the intermediate formed is an alkoxide ion (C-O⁻), which must be protonated to become an alcohol.

This conversion is significant due to the diverse roles alcohols play, ranging from solvents to precursors for other compounds in synthetic chemistry.

Sodium Borohydride Reduction

Sodium borohydride (NaBH₄) is a widely used reducing agent in organic chemistry, particularly for converting carbonyl compounds to alcohols. It is favored for its selectivity and mild reaction conditions.

• Reactant Suitability: NaBH₄ effectively reduces aldehydes, as they are relatively more reactive carbonyl compounds, compared to ketones or esters.
• Reaction Conditions: The reduction is typically carried out in polar protic solvents like methanol or ethanol, which facilitate the reaction by stabilizing the intermediates.
• Safety and Temperature: The reactions are often conducted at low temperatures to prevent side reactions, ensuring a clean product.

NaBH₄ is preferred when working with sensitive substrates, minimizing over-reduction and protecting functional groups.

Reduction Reaction Mechanism

The reduction of aldehydes with sodium borohydride involves a series of steps that transform the carbonyl group into an alcohol. This mechanism details the path taken during the chemical transformation.

• Hydride Donation: The first key step involves the donation of a hydride ion from NaBH₄ to the carbon atom of the carbonyl, forming an alkoxide ion intermediate.
• Alkoxide Ion Formation: This intermediate is represented as R-CH(O⁻), where the negative charge on the oxygen atom is stabilized by sodium (Na⁺).
• Protonation: The alkoxide ion is then protonated in the final step, usually using an acid like water or a dilute acid, to yield the alcohol product.

Understanding the mechanism is crucial for effective manipulation and modification of similar reactions in synthetic applications.

Hydride Ion Donation

In the context of aldehyde reduction, hydride ion donation is a fundamental concept. Sodium borohydride supplies a hydride ion ( H^- ) which is the actual reducing species in the reaction.

• Role of Hydride: The hydride ion acts as a nucleophile, attacking the electrophilic carbon in the carbonyl group, helping break the double bond.
• Stabilization: As the carbonyl carbon receives the hydride ion, the oxygen atom bears a negative charge, stabilized by the polar solvent and sodium ion.
• Reaction Specificity: NaBH₄ provides one hydride ion per equivalent, making it ideal for reducing specific functional groups like aldehydes without affecting others.

Grasping the behavior of hydride ions aids in choosing the right conditions and reagents for targeted organic transformations.