What happens when a primary alcohol is oxidized?

Primary alcohol oxidizes to aldehyde and on further oxidization it gives carboxylic acid

The correct answer is option 1. Primary alcohol oxidizes to aldehyde and on further oxidization it gives carboxylic acid.

Here is a detailed explanation of what happens when a primary alcohol is oxidized:

Oxidation Process:

Primary alcohols \((R-CH_2OH)\) have a hydroxyl group \((OH)\) attached to a primary carbon atom (a carbon bonded to only one other carbon atom). Oxidation involves the removal of electrons from a molecule. In the case of primary alcohols, oxidation involves the removal of a hydrogen atom from the carbon bonded to the hydroxyl group and the oxygen atom from the hydroxyl group.

Step 1: Formation of Aldehyde

During the first stage of oxidation, the primary alcohol loses two hydrogen atoms: One hydrogen comes from the hydroxyl group \((OH)\). The other hydrogen comes from the carbon atom bonded to the hydroxyl group. The oxygen atom from the hydroxyl group remains bonded to the carbon atom, and a double bond forms between them, resulting in a carbonyl group \((C=O)\). This conversion transforms the primary alcohol into an aldehyde \((R-CHO)\).

Step 2: Further Oxidation to Carboxylic Acid

If the oxidation reaction continues with a stronger oxidizing agent or harsher conditions, the aldehyde can be further oxidized. In this step, another oxygen atom is added to the carbonyl group of the aldehyde, forming a carboxylic acid group \((COOH)\).

Additionally, another hydrogen atom is removed from the carbon atom adjacent to the carbonyl group.

This reaction converts the aldehyde \((R-CHO)\) into a carboxylic acid \((R-COOH)\).

Overall Reaction:

The complete oxidation process of a primary alcohol can be summarized by the following equation:

Factors Affecting Oxidation Extent:

The oxidizing agent used plays a crucial role. Milder oxidizing agents like chromic acid \((H_2CrO_4)\) in the presence of sulfuric acid \((H_2SO_4)\) typically stop the reaction after the aldehyde stage.

Stronger oxidizing agents like potassium permanganate \((KMnO_4)\) or potassium dichromate \((K_2Cr_2O_7)\) in acidic media can drive the reaction further, leading to the formation of a carboxylic acid.

Key Points:

Secondary alcohols \((R_2CHOH)\) upon oxidation form ketones \((R_2CO)\) directly, not aldehydes or carboxylic acids.

Tertiary alcohols \((R_3COH)\) are generally resistant to oxidation due to the lack of a hydrogen atom on the carbon bonded to the hydroxyl group.