3.5.3 Oxidation of Alcohols

Question 1

Conditions and results when oxidising alcohols

Answer 1

• K2Cr2O7
• Dilute sulfuric acid (provides H+)
• Orange to green

Or

• KMnO4
• Dilute sulfuric acid (Provides H+)
• Purple to colourless

Question 2

Oxidation of primary alcohols :

Answer 2

• Added to oxidising agent (K2Cr2O7)
• Warmed
• Aldehyde produced, but with lower boiling point than alcohol reactant so needs to be immediately distilled off
• If not distilled, further refluxing occurs and carboxylic acid is formed

Question 3

Oxidation of Secondary Alcohols :

Answer 3

• Added to oxidising agent (K2Cr2O7)
• Warmed
• Ketone produced, but does not need to be distilled off because ketones cannot be further oxidised

Question 4

Tollen’s Reagent

Answer 4

• Aqueous
• Silver Nitrate
• Excess ammonia
• Warmed with aldehyde, oxidised to form carboxylic acid
• Ag+ ions reduced to Ag ions
• Silver mirror forms

Question 5

Fehling’s Solution

Answer 5

• Alkaline
• Cu2+ ions
• Warmed with aldehyde
• Cu2+ reduced to Cu+
• Blue to brick red