Difference Between NaBH4 and LiAlH4 Reaction

The key difference between NaBH4 and LiAlH4 reaction is that NaBH4 is a weak reducing agent, while LiAlH4 is a strong reducing agent.

Both NaBH4 and LiAlH4 are reducing agents. These are the most common sources of hydride nucleophiles we use in organic synthesis reactions. The name of NaBH4 is sodium borohydride while the name of LiAlH4 is lithium aluminum hydride.

CONTENTS

1. Overview and Key Difference
2. What is NaBH4 Reaction
3. What is LiAlH4 Reaction
4. Side by Side Comparison – NaBH4 vs LiAlH4 Reaction in Tabular Form
5. Summary

What is NaBH4 Reaction?

NaBH4 reaction is a type of redox reaction where NaBH4 is the reducing agent. The chemical formula NaBH4 stands for sodium borohydride. It is one of the most common sources of hydride nucleophiles. This compound has a polar metal-hydrogen bond. Therefore, during the redox reaction, we cannot find the hydride anion; thus, this reagent serves as a source of hydride due to the presence of this metal-hydrogen bond. However, when we compare NaBH4 with LiAlH4, the metal-hydrogen bond of LiAlH4 is more polar; thus, it is a stronger reducing agent than NaBH4. This is mainly because aluminum in LiAlH4 is more electronegative than boron in NaBH4.

Sodium borohydride can reduce many organic carbonyl compounds. Typically, this substance is used in the laboratory to convert a ketone or an aldehyde into an alcohol. Moreover, the reactions of NaBH4 can efficiently reduce acyl chlorides, anhydrides, thioesters, and imines at room temperature. Furthermore, NaBH4 reacts with water and alcohols, forming hydrogen gas and a borate salt.

Furthermore, in NaBH4 reactions, an alcohol (such as methanol or ethanol) is used as the solvent for reduction of ketones or aldehydes. However, the reactivity of NaBH4 can be enhanced or augmented by different compounds such as methanol.

What is LiAlH4 Reaction?

LiAlH4 is a type of redox reaction where LiALH4 is the reducing agent. The chemical formula LiAlH4 stands for lithium aluminum hydride. It has four metal-hydrogen bonds which are highly polar due to the difference in the electronegativity between lithium and hydrogen atoms. This makes the compound a strong reducing agent. Moreover, this compound exists as a solid in room temperature where it is extremely reactive towards the water and releases hydrogen gas upon the reaction with water. This reaction is very dangerous due to the high reactivity of the reaction mixture.

LiAlH4 can convert esters, carboxylic acids, acyl chlorides, aldehydes and ketones into their corresponding alcohol. Moreover, it can convert amides, nitrile compounds, azides and nitro compounds into the corresponding amines.

What is the Difference Between NaBH4 and LiAlH4 Reaction?

NaBH4 and LiAlH4 are the most common reducing agents in organic chemistry. The key difference between NaBH4 and LiAlH4 is that NaBH4 is a weak reducing agent, while LiAlH4 is a strong reducing agent. When comparing NaBH4 with LiAlH4, the metal-hydrogen bond of LiAlH4 is more polar; thus, it is a stronger reducing agent than NaBH4. This is mainly because aluminum in LiAlH4 is more electronegative than boron in NaBH4.

Below infographic gives a detailed comparison related to the difference between NaBH4 and LiAlH4.

Summary – NaBH4 vs LiAlH4 Reaction

A reducing agent is a chemical substance that can reduce another substance while oxidizing itself. NaBH4 and LiAlH4 are the most common reducing agents in organic chemistry. The key difference between NaBH4 and LiAlH4 is that NaBH4 is a weak reducing agent, while LiAlH4 is a strong reducing agent.

Reference:

1. Welker, Martin. “Organic Chemistry II.” 3. Reductions Using NaBH4, LiAlH4 | Organic Chemistry II. N.p., n.d. Web. 26 June 2020.

Image Courtesy:

1. “Sodium borohydride” By Kemikungen – Own work (Public Domain) via Commons Wikimedia
2. “Lithium aluminium hydride” By Kemikungen – Own work (Public Domain) via Commons Wikimedia