Carbonyl reduction

Overview

Hydride addition forms a new C-H bond and converts the C=O pi bond into an alkoxide. Protonation then gives methanol without introducing another carbon.

Transformation

Methanal → Methanol

Equation

HCHO + 2[H] -> CH3OH

Reagents

NaBH4; aqueous work-up

Environment

Controlled hydride addition followed by protonation

Reaction class

Carbonyl reduction

Mechanism

nucleophilic hydride addition

Evidence level

source-backed molecular example

Scope and limitations

Scope

The simplest aldehyde gives the simplest alcohol.

Limitations

Methanal in aqueous solution is strongly hydrated; the equation uses its carbonyl form for net structural accounting.

Related reactions

• Grignard addition co reactant: Methanal → Primary alcohols

  Methanal plus a Grignard reagent gives a primary alcohol after acidic work-up.

• Catalytic oxidation: Methanol → Methanal

  Removing hydrogen from methanol creates a carbonyl while retaining its single carbon. Oxygen accepts the removed hydrogen as water in this overall catalytic-oxidation equation.

• Aldehyde oxidation: Methanal → Methanoic acid

  Oxidation changes the aldehyde hydrogen into acid functionality through the hydrated carbonyl. The carbon count stays at one, but further oxidation remains possible.

• Esterification: Methanol → Methyl acetate

  Methanol attacks an acid-activated carbonyl; proton transfers and water loss give methyl acetate. The ester oxygen linking to the methyl group comes from the alcohol.

• Acid hydrolysis: Methyl acetate → Methanol

  Water adds to the protonated ester carbonyl. Proton transfer allows methanol to leave as the carbonyl reforms, producing the acid and alcohol together.

References

1. Organic Chemistry: Nucleophilic Addition of Hydride and Grignard ReagentsJohn McMurry · OpenStax Organic Chemistry · 2023

   Supports hydride addition to aldehydes and ketones followed by protonation to form alcohols; used as the mechanism-pattern source for the aldehyde-to-primary-alcohol template.