Organic Chemistry: Carboxylic Amides Reduction

Questions and Answers

What is the primary function of lithium aluminium hydride (LiAlH4) in organic transformations?

To hydrolyze amides into carboxylic acids

To perform electrophilic aromatic substitution

To oxidize alcohols to aldehydes

To reduce carbonyl groups to alcohols (correct)

In the reduction of β-aryl-α,β unsaturated carbonyl compounds, what is a key outcome when using LiAlH4?

Only the alkene functional group is reduced

Only the carbonyl functional group is reduced

The carbon-carbon double bond remains intact

Both the carbon-carbon double bond and the carbonyl group are reduced (correct)

Which type of compound is formed when propargylic alcohols (R–C≡C–CH2OH) are reduced using lithium aluminium hydride?

Dienes

Saturated alcohols

Trans alkenes (correct)

Aldehydes

How does the mechanism of reduction using lithium aluminium hydride primarily occur?

By nucleophilic attack of hydride on the carbonyl carbon Signup and view all the answers

Which of the following is NOT a common application of lithium aluminium hydride in organic chemistry?

Reduction of alkenes to alkanes Signup and view all the answers

What is the primary effect of adding AlCl3 to LiAlH4 in a mixed lithium aluminium hydride-aluminium chloride reagent?

It lowers the reducing power of LiAlH4. Signup and view all the answers

Which reaction product is formed when LiAlH4 reacts with 3AlCl3?

LiCl and 4AlHCl2 Signup and view all the answers

What can be inferred about the reducing ability of mixed lithium aluminium hydride-aluminium chloride compared to LiAlH4 alone?

The mixed hydride exhibits reduced reducing abilities. Signup and view all the answers

In the context of nucleophilic attack, how does LiAlH4 primarily function?

As a strong nucleophile capable of attacking electrophiles. Signup and view all the answers

Which functional group is readily reduced by lithium aluminium hydride?

Carboxylic acids Signup and view all the answers

Study Notes

Carboxylic Amides Reduction

Carboxylic amides can be converted into amines or aldehydes through reduction.
Lithium aluminium hydride (LiAlH4) is commonly used as the reducing agent, often in tetrahydrofuran (THF) at low temperatures.

Alkene and Carbonyl Compound Reduction

Reducing β-aryl-α,β unsaturated carbonyl compounds using LiAlH4 results in the reduction of both the carbonyl group and carbon-carbon double bond.
Various conditions like temperature adjustments (e.g., -10ºC or 35ºC) can influence the reduction process, with alternative reagents like sodium borohydride (NaBH4) or DIBAL-H also applicable.

Propargylic Alcohol Reduction

Propargylic alcohols are reduced with LiAlH4 to yield trans alkenes.
A mixed lithium aluminium hydride-aluminium chloride reagent can form, altering the reducing power of LiAlH4.

Mixed Hydride Reagent Reactions

Formations like LiAlH3 and other mixed hydrides occur with AlCl3, affecting the reactivity of reducing agents.
For example, the addition of AlCl3 can decrease LiAlH4's ability to reduce functional groups compared to its standalone use.

Lithium Tri-t-butoxyaluminium Hydride

Lithium tri-t-butoxyaluminium hydride ([LiAlH(OtBu)3]) is a milder reducing agent than LiAlH4.
This reagent can reduce various functional groups, with specific outcomes:
- Aldehydes and ketones reduce to alcohols.
- Carboxylic esters, epoxides react slowly.
- Halides, nitriles, and nitro groups typically are not reduced.

Preparation of Lithium Tri-t-butoxyaluminium Hydride

[LiAlH(OtBu)3] is synthesized by reacting lithium aluminium hydride with tert-butyl alcohol, employing a stoichiometric relationship.

Description

This quiz focuses on the conversion of carboxylic amides into amines and aldehydes using lithium aluminum hydride (LiAlH4) as a reducing agent. It tests your understanding of the necessary conditions and outcomes of this organic reaction. Ideal for students delving into organic chemistry mechanisms.