8. Oxidation and reduction of organic compounds

How do alcohols react with oxidizing agents?

They undergo selective oxidation at the carbon attached to the –OH group while maintaining the carbon skeleton.

What is a common oxidizing agent for alcohols?

Acidified potassium dichromate (K₂Cr₂O₇), which changes from orange (Cr(VI)) to green (Cr(III)).

What are the oxidation products of primary alcohols?

They oxidize first to aldehydes and then to carboxylic acids if excess oxidizing agent is used.

What is the oxidation product of secondary alcohols?

They oxidize to ketones.

Can tertiary alcohols be oxidized using K₂Cr₂O₇? Why or why not?

No, because they lack a hydrogen atom on the carbon bonded to the hydroxyl group.

What is reflux, and when is it used?

Reflux is a technique where vapors condense and return to the reaction mixture; used for oxidizing primary alcohols to carboxylic acids or secondary alcohols to ketones.

What is distillation, and when is it used?

Distillation separates a volatile product from a reaction mixture; used to isolate aldehydes before further oxidation.

Why does wine left in the air smell like vinegar?

Bacteria oxidize ethanol to ethanoic acid (acetic acid).

What is the reducing agent used to reduce organic compounds?

• Lithium aluminum hydride (LiAlH₄) or sodium borohydride (NaBH₄).

How can carboxylic acids be reduced?

In a two-step reaction via an aldehyde intermediate, forming a primary alcohol.

How can ketones be reduced?

Ketones reduce to secondary alcohols using reducing agents like LiAlH₄ or NaBH₄.

What is the general reaction for reducing alkenes and alkynes?

Hydrogenation, where hydrogen gas adds to multiple bonds in the presence of a metal catalyst.

What catalysts are used for hydrogenation?

• Nickel (Ni), platinum (Pt), or palladium (Pd).

How does reduction affect the degree of unsaturation in organic compounds?

It decreases unsaturation by converting double or triple bonds into single bonds.

What happens when excess hydrogen reacts with an alkyne?

The alkyne is reduced to an alkane.

What is the product when propene reacts with hydrogen gas?

Propane.

What is the product when pent-1-yne reacts with excess hydrogen gas?

Pentane.

Oxidation

A reaction where a molecule gains oxygen or loses hydrogen.

Reduction

A reaction where a molecule gains hydrogen or loses oxygen.

Oxidizing Agent

A substance that causes oxidation by accepting electrons (e.g., K₂Cr₂O₇).

Reducing Agent

A substance that causes reduction by donating electrons (e.g., LiAlH₄, NaBH₄).

Primary Alcohols

Alcohols where the –OH group is attached to a carbon bonded to one other carbon.

Secondary Alcohols

Alcohols where the –OH group is attached to a carbon bonded to two other carbons.

Tertiary Alcohols

Alcohols where the –OH group is attached to a carbon bonded to three other carbons.

Aldehyde

• A compound with a carbonyl group (C=O) at the end of a carbon chain.

Ketone

A compound with a carbonyl group (C=O) within a carbon chain.

Carboxylic Acid

compound with a carboxyl group (-COOH).

Hydrogenation

• A reduction reaction where hydrogen gas is added to unsaturated compounds.

Alkyne to Alkane Conversion

The reaction where an alkyne is completely reduced to an alkane using excess hydrogen gas.