OCR - A-Level - Chemistry - Oxidation of Alcohols

Primary Oxidation

• 
• Caption: (Potassium) Dichromate changes from orange to green.
• Gently heat alcohols in the presence of an oxidising agent (such as potassium dichromate) and then distil immediately in acidic conditions.
• It forms an aldehyde and water.
• Heating further under reflux and using an excess of the oxidising agent. Reflux involves using equipment that boils and then condenses the alcohol.
• It forms a carboxylic acid and water.

Secondary Oxidation

• 
• Heat alcohol intensely under reflux and in the presence of an oxidising agent. Intense heating is necessary because secondary alcohols are more stable.
• It forms a ketone and water.
• Caption: (Potassium) Dichromate changes from orange to green.

Tertiary Oxidation

• Even under the same conditions as the previous two, no reaction occurs. This is because there are already 3 bonds to carbon atoms, meaning it will not form anything else. This is the most stable.
• 
• Caption: There will be no change to the dichromate because no reaction occurs.

Summary

• Under reflux:
• > If primary alcohol - end up as carboxylic acid, with aldehyde in between - orange to green dichromate.
• > If secondary alcohol - end up as ketone - orange to green dichromate.
• > If tertiary alcohol - no reaction, remains as alcohol - no change dichromate.