Overview
This lecture explains how aldehydes can be oxidized to carboxylic acids, the role of acidified dichromate as the oxidizing agent, and how this reaction distinguishes aldehydes from ketones.
Oxidation of Aldehydes
- Aldehydes can be oxidized to carboxylic acids.
- Example: Ethanal is oxidized to ethanoic acid.
- Acidified dichromate (Cr2O7^2- with H+) is the oxidizing agent used.
- Both potassium dichromate and sodium dichromate, with dilute sulfuric acid, can act as sources of the oxidizing agent.
- The dichromate ion is orange and turns green when reduced to chromium(III) ion.
Reaction Conditions and Observations
- Gentle warming is enough for aldehyde oxidation, but reflux with excess oxidizing agent is used to ensure complete reaction.
- After oxidation, distillation purifies the carboxylic acid product.
- In equations, the oxidizing agent is shown as [O].
Distinguishing Aldehydes from Ketones
- Ketones cannot be oxidized by acidified dichromate.
- Oxidation with acidified dichromate can test for the presence of an aldehyde if only aldehyde or ketone is in the sample.
- More reliable chemical tests exist for distinguishing aldehydes from ketones.
Key Terms & Definitions
- Aldehyde — Organic compound with a carbonyl group bonded to at least one hydrogen atom.
- Ketone — Organic compound with a carbonyl group bonded to two carbon atoms.
- Carboxylic acid — Organic acid containing a carboxyl group (COOH).
- Acidified dichromate — Dichromate ion (Cr2O7^2-) in acidic solution, used as an oxidizing agent.
- Reflux — Heating a reaction mixture while condensing vapors back to liquid.
- [O] — Symbol representing an oxidizing agent in chemical equations.
Action Items / Next Steps
- Watch the previous video on the structure of aldehydes and ketones if not already viewed.
- Prepare for the next lecture on the reduction of carbonyl compounds.