Reduction of Vanillin Acetate Flashcards

What is a reduction?

Gain of H (hydrogen) or loss of O.

What functional groups are important to consider?

Aldehydes, ketones, esters, and amides.

What is a hydride?

H⁻ (a hydrogen with two electrons) that attacks a carbonyl.

What are the characteristics of a hydride?

Electron-rich and acts as a nucleophile.

What are the two common reducing agents?

NaBH₄ and LiAlH₄.

How do NaBH₄ and LiAlH₄ differ?

NaBH₄ reduces aldehydes and ketones. LiAlH₄ is stronger and also reduces esters and amides.

What is the general mechanism of hydride reduction?

Hydride attacks the carbonyl carbon, then the oxygen is protonated to form an alcohol.

Why are reducing agents water sensitive?

They react with water and lose effectiveness.

Where/how are reducing agents stored & why?

In a desiccator to keep moisture away

What is a desiccator?

A sealed container with a drying agent that removes moisture.

How many equivalents of reducing agent are needed to reduce one carbonyl?

- ¼ equivalent of NaBH₄ (1 mole NaBH₄ can reduce 4 moles of C=O).

Why do we add excess NaBH₄?

Some reacts with ethanol and moisture, so extra ensures the reaction finishes.

Why do we cool the vanillin acetate/ethanol solution before adding NaBH₄?

To slow the reaction and keep NaBH₄ from reacting too quickly.

Which solvent is more polar: ethyl acetate or hexanes?

Ethyl acetate

How can you tell ethyl acetate is more polar?

It contains oxygen; hexanes are nonpolar hydrocarbons.

What is TLC?

Thin Layer Chromatography.

What is the purpose of TLC?

To check reaction progress and purity.

What are the basic principles of chromatography?

Compounds move different distances because they have different polarities.

If making 10 mL of a 1:4 ethyl acetate:hexanes mixture, how much of each is needed?

2 mL ethyl acetate and 8 mL hexanes.

What is Rf?

Distance traveled by the compound/distance traveled by the solvent.

What are we checking for with TLC?

Whether all the reactants has disappeared.

Would Rf change if a larger TLC plate was used?

No

Why shouldn't we use pen on TLC plates?

Ink dissolves and interferes with results.

What should the TLC plate look like when the reaction is complete?

Only the product spot remains; the reactant spot is gone.

Which spot is higher on the TLC plate?

The less polar compound.

Why do we add water after the reaction?

To quench the reaction and destroy excess NaBH₄.

Why do we add ether?

To extract the organic product.

What goes into the aqueous layer?

Water, salts, and other water-soluble compounds.

Why wash the ether layer with sodium bisulfite?

To remove any unreacted aldehyde.

If this reaction used LiAlH₄ instead of NaBH₄, what changes would be needed?

No water or alcohol; completely dry conditions are required.

What happens if LiAlH₄ is used with water or alcohol?

It reacts violently.

How do you prepare an IR sample?

Place a small drop of the product on the IR crystal.

How much sample is needed for IR?

One small drop.

What is a background in IR?

A blank scan taken before the sample.

What should the IR spectrum look like?

The aldehyde C=O peak disappears, and a broad alcohol O–H peak appears. The ester C=O remains.