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Aromatic Side Chain Oxidation
Transcript of Aromatic Side Chain Oxidation
What is Oxidation?
Oxidation - loss of electrons; increase in oxidation state
Results and Discussion
Refluxing the KMnO4 and xylene mixture for 1.5 hours applied energy to facilitate the reaction.
reaction with oxygen to form oxide
first known oxidizing agent
Most oxidation reactions necessitate either a heteroatom in a reduced state
However, the oxidation of an
aromatic side chain
does not require any of these molecules or atoms. It only requires a benzylic carbon with attached hydrogen of at least one.
Phthalic Acid from Xylene
Filter and Dry
Hydrochloric acid was added drop by drop in order to protonate the benzoate ions, giving rise to benzoic acid.
Benzoic acid has high solubility in xylene at high temperatures.
In case too much xylene was added, the solution was heated to evaporate excess xylene to ensure supersaturation of benzoic acid at room temperature.
Guide Questions and Answers
1. Do all aromatic hydrocarbons give rise to benzoic acid upon oxidation by potassium permanganate? If not, what type of alkyl chains does not give carboxylic acids?
2. Why did we use potassium permanganate instead of sodium dichromate solution?
3. Show a correctly balanced oxidation-reduction equation for this reaction. It is easiest to determine the oxidation state of the methyl carbon of the toluene, and the carbonyl carbon of the acid. Also, determine the oxidation states for the Mn in both the permanganate ion and the MnO2. Balance the equation based on the correct number of electrons gained, and lost.
Conclusion and Recommendation
Xylene produces phthalic acid upon oxidation with KMnO4. It's configuration depends on the position of the methyl groups of the xylene.
Recrystallization of benzoic acid requires the right amount of solvent such as xylene.
Evaportion of excess xylene should be done in a hood because inhalation of xylene vapor has various hazards to health.
If the weight of benzoic acid were determined, it is expected to be less than the stoichiometric equivalent of xylene molecules.