1. Organic Chemistry Lab II, Spring 2010
The Oxidation of Toluene Microscale Oxidation of Toluene to Benzoic Acid (Reaction of an Aromatic Side Chain)
Organic Chemistry Lab II, Spring 2010
Dr. Milkevitch
April 12 & 14, 2010

2. Today’s Experiment
Conduct an oxidation of a group attached to an aromatic ring
Convert an alkyl group on an aromatic ring to a carboxylic acid group
Purpose of the experiment
Review aromatic compounds
Their structure, stability, reactivity
Demonstrate an oxidation of an aromatic side chain
Selectively oxidize a group on an aromatic ring
Leaving the aromatic ring intact (unoxidized)

3. Reactions of Benzene, (con’t)
There are many reactions of benzene
Last week: examined electrophilic aromatic substitution
Today: Oxidize aromatic side chain
Remember:
Benzene does not react like a conjugated cyclic triene
You can oxidize an alkene, but not a benzene ring
With potassium permanganate

4. Oxidation of Benzene Side Chains
Benzene ring resistant to oxidation
By strong oxidants like potassium permanganate
Not so with alkyl side chains on aromatic rings
Reactions take place at benzylic carbons
Benzylic carbon must have at least one hydrogen
Intermediates: benzylic radicals or benzylic carbocations
Mechanism not well understood

5. This Experiment
Oxidant: potassium permanganate
Substrate is toluene

6. Cautions!!! Potassium permanganate Strong oxidizer Avoid contact!
Will stain skin and clothing
Its seriously purple!

7. Procedure I Into a 10 ml RB flask, place:
825 mg of potassium permanganate
100 mg of sodium carbonate
3 ml of water
Small spin bar
Attach reflux condenser to flask
Attach heating mantle
Dissolve reagents with gentle stirring/heating
Turn off heat, let cool ~ 3 min
Add 250 microliters of toluene
Approx 10 mg of detergent
Aids mixing of toluene and water
Reflux with stirring for 45 min
Do not overheat, for it can “bump”

8. Procedure II Formal lab report required
Most of the purple color should be gone by the end of the reflux
Turn off water to condenser
While still warm:
Add sodium bisulfite until the purple color is gone
Filter off MnO2 using a Hirsch funnel containing Celite
Celite is a filter aid
Keeps filter paper from clogging
See the lab TA or myself for Celite
Rinse flask with 0.5 ml of ddH2O, add this to filtrate
Check filtrate:
Filtrate is what you want!
If its still purple colored, add sodium bisulfite until the solution is colorless
Filter solution again if more brown precipitate forms
Cool filtrate in ice
Acidify with 1 ml of concentated HCl
Collect crystals by vacuum filtration using a Hirsch funnel
Wash crystals with 1 ml of cold water
Recrystalize from water
Dry crystals, weigh and take a melting point
Formal lab report required