How Do NaBH4, LiAlH4, and DIBAL Differ in Reductions?

TL;DR

Sodium borohydride (NaBH4) is a mild reducing agent that reduces aldehydes, ketones, and acid chlorides to alcohols, while lithium aluminum hydride (LiAlH4) is a stronger agent that can also reduce esters and amides. DIBAL (diisobutyl aluminum hydride) selectively reduces esters to aldehydes without affecting ketones, making it useful for specific selective reductions.

Transcript

in this video we're going to focus on reducing agents such as nabh4 sodium borohydride or lialh4 lithium aluminum hydride and even dibol so let's begin let's say if we have three compounds a ketone specifically cyclohexanone an aldehyde and a carboxylic acid we're going to react each of these with sodium borohydride now you need to know that nabh4 ... Read More

Key Insights

• ❓ Sodium borohydride is a mild reducing agent that can reduce aldehydes, ketones, and acid chlorides to alcohols.
• 💪 Lithium aluminum hydride is a stronger reducing agent that can reduce aldehydes, ketones, acid chlorides, esters, and amides to alcohols.
• 🇪🇭 Dibol, or diisobutyl aluminum hydride, is a selective reducing agent that can reduce esters to aldehydes without affecting ketones.
• 🫀 Reduction of ketones and aldehydes involves the addition of one hydrogen atom, while reduction of acid chlorides and esters involves the addition of two hydrogen atoms.
• 💁 The mechanisms of reduction involve the attack of hydride ions on the carbonyl carbon, followed by the formation of a tetrahedral intermediate.
• 😑 Protonation of the intermediate with water or hydronium ions yields the alcohol product.

Questions & Answers

Q: What compounds can sodium borohydride reduce?

Sodium borohydride can reduce aldehydes, ketones, and acid chlorides to alcohols by adding one or two hydrogen atoms, depending on the compound.

Q: Can sodium borohydride reduce carboxylic acids or esters?

No, sodium borohydride cannot reduce carboxylic acids or esters. It lacks the reactivity to add hydrogen atoms to these functional groups.

Q: What compounds can lithium aluminum hydride reduce?

Lithium aluminum hydride can reduce aldehydes, ketones, acid chlorides, esters, and even amides to alcohols by adding one or two hydrogen atoms, depending on the compound.

Q: How does the reactivity of sodium borohydride and lithium aluminum hydride differ?

Sodium borohydride is a milder and less reactive reducing agent compared to lithium aluminum hydride. Lithium aluminum hydride is more powerful and can reduce a broader range of functional groups.

Q: What is the purpose of using dibol instead of lithium aluminum hydride?

Dibol, or diisobutyl aluminum hydride, is a selective reducing agent that can specifically reduce esters to aldehydes without affecting ketones. It is used to target the reduction of esters while preserving other functional groups.

Summary & Key Takeaways

• Sodium borohydride (NaBH4) is a mild reducing agent that can reduce aldehydes, ketones, and acid chlorides to alcohols.

• Lithium aluminum hydride (LiAlH4) is a stronger reducing agent that can reduce aldehydes, ketones, acid chlorides, esters, and even amides to alcohols.

• Dibol, or diisobutyl aluminum hydride (DIBAL-H), is a selective reducing agent that can reduce esters to aldehydes without reducing ketones.