Problem 72 - Chemistry and Chemical Reactivity

Question

Draw the structure and name the product formed if the following alcohols are oxidized. Assume an excess of the oxidizing agent is used. If the alcohol is not expected to react with a chemical oxidizing agent, write NR (no reaction). (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (b) 2-butanol (c) 2 -methyl-2-propanol (d) 2 -methyl-1-propanol

Step-by-Step Solution

Answer

(a) Butanoic acid, (b) Butanone, (c) NR, (d) 2-Methylpropanoic acid.

Step 1: Identify the type of alcohol (a)

The compound \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} \) is a primary alcohol because the hydroxyl group (\(\mathrm{OH}\)) is attached to a carbon that is only connected to one other carbon chain.

Step 2: Oxidize the primary alcohol

When a primary alcohol such as \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} \) is oxidized, it first forms an aldehyde and after complete oxidation in excess oxidizing agent, it forms a carboxylic acid. The final oxidized product is \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH} \), named butanoic acid.

Step 3: Identify the type of alcohol (b)

2-butanol is a secondary alcohol because the \(\mathrm{OH}\) group is attached to a carbon that is connected to two other carbons.

Step 4: Oxidize the secondary alcohol

Upon oxidation, 2-butanol forms a ketone. The product for the oxidation of 2-butanol is \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\), which is called butanone.

Step 5: Identify the type of alcohol (c)

2-methyl-2-propanol is a tertiary alcohol because the carbon with the \(\mathrm{OH}\) group is attached to three other carbons.

Step 6: Determine the reactivity of the tertiary alcohol

Tertiary alcohols do not react with oxidizing agents under normal conditions because there's no hydrogen atom on the carbon atom with the hydroxyl group to be abstracted. Therefore, the result for 2-methyl-2-propanol is NR (no reaction).

Step 7: Identify the type of alcohol (d)

2-methyl-1-propanol is a primary alcohol since the \(\mathrm{OH}\) is attached to a carbon bonded to one other carbon.

Step 8: Oxidize the primary alcohol

Upon oxidation, 2-methyl-1-propanol forms first an aldehyde, then a carboxylic acid in the presence of an excess oxidizing agent. The final product is \(\mathrm{(CH_{3})_{2}CHCOOH}\), which is called 2-methylpropanoic acid.

Key Concepts

Primary Alcohols

Primary alcohols are molecules where the hydroxyl group \( (\text{OH}) \) is attached to a carbon atom that is only bonded to one other carbon. These alcohols can be oxidized quite readily. During oxidation, a primary alcohol first undergoes a transformation to an aldehyde. If the oxidation continues in the presence of an excess oxidizing agent, the aldehyde further oxidizes to form a carboxylic acid.

• An example of a primary alcohol is butanol \( (\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH}) \).
• When butanol is oxidized, it first turns into butanal \( (\text{CH}_3\text{CH}_2\text{CH}_2\text{CHO}) \).
• Further oxidation with excess reagent converts butanal into butanoic acid \( (\text{CH}_3\text{CH}_2\text{CH}_2\text{COOH}) \).

This transformation involves the removal of hydrogen atoms and the addition of oxygen, which is essentially what oxidation in organic chemistry typically means. Primary alcohols are excellent candidates for oxidation reactions due to the presence of a hydrogen atom on the carbon bearing the \( \text{OH} \) group.

Secondary Alcohols

Secondary alcohols contain a hydroxyl group attached to a carbon atom that is connected to two other carbon atoms. When oxidized, secondary alcohols form ketones. Unlike primary alcohols, secondary alcohols do not further oxidize beyond the ketone stage under normal conditions.

• 2-butanol \( ((\text{CH}_3\text{CHOHCH}_2\text{CH}_3)) \) is an example.
• Oxidizing 2-butanol results in butanone \( (\text{CH}_3\text{COCH}_2\text{CH}_3) \).

The oxidation of secondary alcohols involves converting the \( \text{C-OH} \) group into a \( \text{C=O} \) group, transforming the alcohol into a ketone. However, it is crucial to note that the secondary carbon lacks a hydrogen directly bonded to undergo further oxidation into a carboxylic acid as primary alcohols do.

Tertiary Alcohols

Tertiary alcohols are characterized by a hydroxyl group attached to a carbon atom that is bonded to three other carbon atoms. A key feature of tertiary alcohols is their resistance to oxidation under normal conditions. This is because there isn't a hydrogen atom on the carbon with the \( \text{OH} \) group that can be removed during oxidation.

• An example is 2-methyl-2-propanol \( ((\text{CH}_3)_3\text{COH}) \).
• Instead of oxidation, tertiary alcohols often undergo alternative reactions or remain unreacted marked as NR (no reaction) in oxidative conditions.

The lack of a direct hydrogen on the carbon atom carrying the hydroxyl group in tertiary alcohols means oxidation cannot occur like it does in primary and secondary alcohols. Hence, they are stable towards oxidizing agents, making them uniquely different in their chemical behavior.