2-pentanol is the chemical compound that would produce 2-pentanone upon oxidation.
The Oxidation of Secondary Alcohols to Ketones
The formation of 2-pentanone from an oxidation reaction points directly to a secondary alcohol as its precursor. In organic chemistry, secondary alcohols are distinguished by having the carbon atom bonded to the hydroxyl (-OH) group also bonded to two other carbon atoms. When oxidized, these secondary alcohols lose two hydrogen atoms—one from the hydroxyl group and one from the carbon atom bearing the hydroxyl group—to form a carbonyl (C=O) group, resulting in a ketone.
Identifying the Precursor: 2-Pentanone
2-Pentanone is a ketone with the molecular formula C₅H₁₀O and the structure CH₃COCH₂CH₂CH₃. The carbonyl group is located on the second carbon atom of a five-carbon chain. To form this structure through oxidation, the starting alcohol must have the hydroxyl group on the second carbon atom of a five-carbon chain. This compound is 2-pentanol.
The chemical transformation is as follows:
CH₃CH(OH)CH₂CH₂CH₃ (2-pentanol) + [O] → CH₃COCH₂CH₂CH₃ (2-pentanone) + H₂O
Here, [O] represents an oxidizing agent.
Common Oxidizing Agents
Various oxidizing agents can facilitate the conversion of a secondary alcohol to a ketone. The choice of reagent often depends on the desired selectivity and reaction conditions. Some common examples include:
- Pyridinium Chlorochromate (PCC): A mild and selective oxidizing agent often used to convert primary alcohols to aldehydes and secondary alcohols to ketones without further oxidation.
- Jones Reagent: A solution of chromium trioxide (CrO₃) in sulfuric acid and acetone. It is a stronger oxidizing agent that effectively converts secondary alcohols to ketones and primary alcohols to carboxylic acids.
- Potassium Dichromate (K₂Cr₂O₇) or Sodium Dichromate (Na₂Cr₂O₇): In the presence of sulfuric acid, these reagents are commonly used for the oxidation of secondary alcohols to ketones.
- Swern Oxidation: A mild and highly selective oxidation reaction that uses oxalyl chloride, dimethyl sulfoxide (DMSO), and a base to convert alcohols to ketones or aldehydes.
What Happens When 2-Pentanone is Further Oxidized?
While 2-pentanol oxidizes to 2-pentanone, ketones themselves can undergo further oxidation under more vigorous conditions, leading to the cleavage of carbon-carbon bonds. For instance, if 2-pentanone is subjected to strong oxidizing agents like concentrated nitric acid, the carbon chain can break. The products formed depend on where the bond cleavage occurs relative to the carbonyl group.
When 2-pentanone is oxidized with concentrated nitric acid, the carbon-carbon bonds adjacent to the carbonyl group are susceptible to cleavage. Specifically, the oxidation of 2-pentanone under such conditions yields propanoic acid (CH₃CH₂COOH) and ethanoic acid (CH₃COOH). This is because the C-C bond on either side of the ketone group (C1-C2 or C2-C3) can break, leading to smaller carboxylic acid fragments.
| Original Bond | Cleavage Products |
|---|---|
| C1-C2 | Ethanoic Acid |
| C2-C3 | Propanoic Acid |
This highlights that while secondary alcohols readily convert to ketones, the ketones themselves can be broken down into smaller carboxylic acids under harsh oxidation conditions.
